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Parasitology
The study of the most common mode of life on earth
Centered on animal parasites of humans, domestic animals and wildlife
Parasite
An organism that lives in or on another organism (host) and can either harm or live off the host at the host’s expense
Why is parasitology important
Parasite resistance
Insecticide resistance
Increased Mobility (popularity in tropics and subtropics)
Migration of refugees from war-torn areas
Military service personnel coming home from abroad
Modifications of the environment
Climate change (disease causing parasites spread from tropics and more temperate regions)
Immunosuppression becoming more widespread:
AIDS; Cancer chemotherapy; and organ transplantation
Indiscriminate release of toxic chemicals and carcinogens into the environment
Cuckoo birds (Cuculus Canorus)
place eggs in other compatible bird’s nest when the parent birds are away
The Candiru (Vandellia Cirrhosa)
is a parasitic fish that attaches to fish urethra because they are attracted to urrea and feed off of the host fish blood. There Have been instances of them latching onto human ureters.
Lessonae
Likes Stagnant Water
Is the host
Competes with Esculentus without passing genes
Ridibundus
Likes moving water
Is the parasite
Passes genes to Esculentus
Esculentus
Can live in both moving and stagnant water
Encroaches on lessone and does not transfer their genes
Parasitologist
Quant person who seeks truth in strange places
Symbiosis
Interactions among organisms in which one organism lives with, in or on the body of another
Symbionts
Organisms involved in symbiotic relationships with other organisms, the host
Neutralism
Is a lack of benefit or detriment experienced by either members of the pair of interacting organisms.
It describes interactions where the fitness of one species has absolutely no effect whatsoever on that of the other.
Competiton
Some degree of overlap in ecological niches of two populations in the same community, such that both depend on the same food source, shelter, or other resources, and negatively affect each other’s survival
Carnivorous animals compete for prey
Plants compete for sunlight, water, nutrients, pollinators, and dispersers of fruits and seeds
The bladderwort plant (Utricularia) competes with tiny fishes for small arthropods.
Phoresis
Form of symbiosis when the symbiont (phoront) is mechanically carried about its host: neither is physiologically dependent on the others
Means “to carry”
Ex. Bacteria on legs of a fly
Ex. Fungal spores on feet of a beetle
Aquatic snail eggs laid on birds feet
Dermatobia hominis (Human botfly)
Protocooperation
A mutually beneficial symbiosis between organisms in which the interaction is NOT physiologically necessary to the survival of either
Egyptian plover eats residuals from crocodile teeth
Cattle egret remove ectoparasites from the back of antelope & Cow
Hermit crab shell covered with sea anemones
Ant and aphids with honeydew
Mutualism
Type of symbiosis In which both host and symbiont benefit from association
Usually Obligatory
In most case there is physiological dependence
Must Know
Termites and intestinal protozoan fauna
Blood-sucking leeches and intestinal bacteria
Cleaning symbiosis: Cleaner Wrasse (Labroides Dimidiatus)
Lichen: Microscopic green algae or cyanobacteria and filamentous fungi
Commensalism
A kind of symbiosis in which the symbiont (a commensal) benefits, and the host is neither harmed nor helped by the association
Means “Eating at the same table”
Pilot fish and remoras
Barnacle on a whale
Epiphytes on a tree
Entamoeba gingivalis
Amensalism
Asymmetrical interaction in which one organism causes a negative effect on another without being positively or negatively affected in return
Bread mold Penicillium that produces penicillin, an antibiotic that kills bacteria
Black walnut tree (Juglans nigra) produces juglone, an organic compound that is toxic or growth-stunting to many types of plants.
Predation
Animal interaction in which a predator kills its prey outright; it does not subsist on the prey while the prey is alive
Parasitism
A symbiosis in which a symbioint benefits from the association, while it harms the host in some way or lives at the expense of the host
Macroparasites
Large parasites that do NOT multiply in the host of interest
Do NOT induce lasting immunity (some exceptions)
Have more stable populations, and cause endemic diseases
Helminthes, arthropods, and other metazoans
Microparasites
Small (or very small) parasite that multiplies within the host of interest
Induce lasting immunity
Have unstable populations, and cause epidemic diseases
Fungi, protists, bacteria, and virus
Ectoparasites
Parasites that live on the outer surface of its host
Endoparasites
Parasite that lies in the host
Obligate parasites
They cannot complete their life cycle without spending at least part of the time in a parasitic relationship
Facultive parasites
Not normally parasitic but can become so when they are accidentally eaten or enter a wound or other body orifices
Accidental (incidental) parasite
A parasite found in host other than its normal host
Puts host and parasite into environmental conditions to which neither is well adapted
Permanent parasite
A parasite that lives its entire adult life within or on a host
Temporary (intermittent) parasite or micro predators
A parasite that contacts its host only if you feed and then leave
Parasitoid
Organism that is a typical parasite early in its development, but finally kills its host during or at the completion of its early development
Often used in reference to many insect parasites of other insects
Approximately 10% of described insect species are parasitoids.
Hyperparasitism
Condition in which an organism is a parasite of another parasite
Coelozoic
A parasite living in the lumen of a hollow organ
Histozoic
A parasite living within the tissues of a host
Vector
A any agent, such as water, wind or insect (host), that transmits a disease organism
Definitive Host
Host in which a parasite achieves sexual maturity; if there is no sexual reproduction in the life of the parasite. This is the most important host
Intermediate Host
Host where the parasite develops some but fully to sexual maturity
Paratenic (transport) host
Host in which a parasite survives without undergoing further development
Reservoir Host
Serves as a means of sustaining a parasite when it is not infecting humans, which is usually also another definitive host
Urban (domestic) Cycle
Normal to human environment
Involves domesticated animals
Sylvatic cycle
Existing normally in the wild
Involves wildlife
Population
Any group of individuals, usually of a single species, occupying a given area at the same time
Mutation
A permanent change in a cell’s DNA and includes: changes in nucleotide sequences, alternation of gene position, gene loss, or duplication, and insertion of foreign sequences
Selective Values (Adaptive Value)
A relative reproductive success (relative fitness) of an allele or genetype as compared to other alleles or genotypes
Preadaptation
The possession of a trait that coincidentally predisposes an organism for survival in an environment different from those encountered in its evolutionary history; may occur because a natural population carries a huge quantity of genetic variability
Dinosaurs feathers initially used for insulation and display
Origin of larynx initially helped air-breathing fish gulp air
Adaptation
An evolutionary process whereby a population becomes better suited to its habitat over many generations
An anatomical structure, a physiological process, or behavioral trait that promotes the likelihood of an organism’s survival and reproduction in a particular environment.
Adaptation of parasites to host internal environments.
Selection
A composite of all the forces that cause differential survival and differential reproduction among genetic variants (artificial selection vs. Natural selection); a key mechanism of evolution
Reciprocal selection pressures exists between parasites and their hosts
Evolution
Genetic changes in populations of organisms through time that leads to differences among them
Evolution only occur when there is a change in gene frequency within a population over time
These genetic differences are heritable and can be passed onto the next generation.
t is in the best interest of the parasite to possess adaptations that allow it:
Encounter the host
Parasites that possess a genetically determined behavioral trait that increases the probability of encountering the host
Allow the parasite to live in the host
Is the best interest of the host to possess adaptations that allow it
Avoid encountering the parasite
To get rid of the parasite if encounter has taken place
Red Queen Hypothesis
Originally proposed by Leigh Van Valen (1973)
Metaphor of alice and the Red Queen
Species have to “run” (evolve) in order to stay in the same place (extant)
Cessation of change may result in extinction
Ex. Parasite-Host Coevolution
Each time the parasite population acquires a new “weapon”, the host population is led to produce a new defense.
Parasite and host populations are engaged in an “endless” arms race/ war
Reproductive
Produces more eggs and sperms than their free-living relatives do
Higher reproductive potential
Asexual reproduction
Hermaphroditism
Self-Fertilization
Behavioral
Adaptive advantage of parasite behavior
Parasite may alter host behavior
Morphological adaptions
Size- Many parasites are larger than their free-living relatives
Attachment organs- Suckers, hooks & spines, penetration organs, and cysts, etc
Loss (regression) of anatomical Structure- Organs of sense, locomotion, digestion, etc
Biochemical adaptations
Energy Metabolism - Catabolic pathways are usually reduced or modified in many parasites
Nutrient Uptake- There is an elaboration of a transport mechanism for acquiring monomers / Ex. Glucose, amino acids, etc
Synthetic reactions- Synthetic capacities of parasites are reduced when compared with their free-living relatives.
Immunological Adaptions
Absorption of host antigen
Antigenic variation
Occupation of immunologically privileged sites
Disruption of the host’s immune response
Molecular mimicry
Loss of masking of surface antigens
Life cycle adaptations
Reduction in the extent of the free-living phase of the life cycle
Behavioral responses to locate favorable environments
Responding to chemical stimuli from their host
Changing the behavior of the infected intermediate host to increase the chances of them being eaten by the final host
Infection of secondary and tertiary hosts (why??)
Increased reproductive potential, since asexual reproduction can take place in the intermediate host
Increase the range of the parasite in space and time
By infecting more than one host species the parasite can survive when one host is scarce
An intermediate host can channel to a definitive host if not enough.
Descriptive parasitology
Studies performed that are non-hypothesis driven;
Includes the discovery of: New Parasites
Parasite morphology
Life Cycle trends
Population survey of infected or non infected hosts
Proper identification of parasites and host is essential in trying to control diseases
It is Naive to try to control an infection without knowledge of how the parasite reproduces and gets from one host to another.
Binomial nomenclature
A system in which a species is given a compound name
Carolus Linnaeus (1701-1778), father of modern taxonomy
1st word is the genus in which the species is placed (first letter capitalized)
2nd word is the species epithet (uncapitalized) used to separate a species from other members of the same genus
Named of genera and lower taxa are always
Taxomony
Study of scientific classifications; ordering & naming organisms
Basic sub discipline of biology
Scientific name carries with it massive amounts of information
Includes (1) through (4)
Describe organism in detail
Provide scientific names for new species
Preserve collections (permanent slides and voucher specimens)
Classification of the organism, keys for their identification, and data on their distributions
Investigates their evolutionary histories
Considers their environmental adaptations
Systematics
Study of classification & biological diversity within an evolutionary context
Seek to understand the origin of diversity at all levels of classification
Includes (1) through (6)
Describe organisms in detail.
Provide scientific names for new species
Preserve collections (permanent slides and voucher specimens)
Classification of the organism, keys for their identification, and data on their distributions
Investigates their evolutionary histories
Considers their environmental adaptations
Phylogenetic Systematics (Cladistics)
Is a Methodology used by systematists to infer (hypothesize) a species evolutionary history (phylogeny)
Pioneered by Willi Hennig (1913-1976)
Used in the discovery of monophyletic groups (evolutionarily real entities)
This method relies on shared derived character states (Homology)
3 Basic assumptions in cladistics
Change in characteristics occur in lineages or groups over time.
Only when characteristics change are we able to recognize different lineages
Any group of organisms are related by descent from a common ancestor.
Supported by many lines of evidence
There is a bifurcating or branching pattern of cladogenesis.
When a lineage splits, it divides into two exactly groups
Phylogeny
Evolutionary hypothesis of the origin and diversification of a taxon
Treelike diagram
Relationships between taxa are shown in the branching patterns
Characters among the taxa used to produce phylogenies include: (anatomical, behavioral, physiological, or molecular attributes)
Clade
Ingroup
Outgroup
Node
Sister Group
A group of organisms that includes an ancestor and all descendants of that ancestor
A taxon of Interest
A related taxon for the purpose of comparison, more basal
Internal branch point that represents the common ancestor of those descendents; a speciation event
Two descendents that split from the same node
Homologous Character
Analogous Character
A character is similar in two taxa because their common ancestor had that character
A similar character that has the same function but different evolutionary origin
Homoplasy
Is similarity NOT due to homology; resulting from convergence, parallelism or reversal
Pleasiomorphic
Ancestral Characters; present in both the ingroup and outgroup
Uninformative Character
Autopomorphic
Derived Character, evolutionary novelty; present only in one taxon of the ingroup
Uninformative Character
Synapomorphies
Shared derived characters that set a taxon apart from related taxa and their most recent common ancestor
Informative character
Monophyletic
Paraphyletic
Polyphyletic
A group of taxa that includes a hypothetical ancestral taxon and all its descendants
Defined by a suite of shared-derived characters (Synapomorphies)
A group of taxa that includes a hypothetical ancestor but does not include all of the ancestor’s descendants
Defined by a suite of ancestral traits
3. A group of taxa that do not share a most recent common ancestor
Defined by convergent traits (homoplasies)
Immune System
A functional system who components attack foreign substances or prevent their entry into the body
Immunity
Stat in which a host is more or less resistant to an infective agent
Used in reference to resistance arising from tissues that are capable of recognizing and protecting the animal against nonself invaders
Innate immunity
A mechanism of defense that does not depend on prior exposure to the invader
Adaptive (acquired) immunity
A mechanism of defense that is specific to the particular nonself material: requires time fore development, and occurs more quickly and vigorously on secondary response
I. Non specific Immunity (Innate immunity)
First Line of defense
Skin
as an effective barrier against pathogens
Oil & Sweat glands give skin surface pH of 4-5.5
Sweat conations lysozyme (Digest bacterial cell wall)
Normal Flora include non-pathogenic bacteria & fungi
Epidermis 10-30 cells thick, dermis 15-40 times thicker
I. Non specific Immunity (Innate immunity)
First Line of defense
Mucosal surfaces
an an effective barrier against pathogens
A.) Digestive Tract
Saliva Contains lysozyme (also in tears)
Acidic environment of stomach pH 1.5-3.5 (Concentrated HCl solution)
Digestive enzymes in intestine
Nonpathogenic normal flora
Vomiting & diarrhea may expel pathogens
B.) Respiratory tract
Pathogens trapped by mucus in bronchi and bronchioles
Ciliated epithelial cells sweep mucus toward the glottis
Coughing and sneezing expels pathogens
C.) Urogenital tract
Viginal secretion viscous and acidic
Secretions promote growth of normal flora
Acidic urine of both sexes may wash out pathogens
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
1.) Phagocytes, inflammation, complement & interferon, cytokines & chemical signals, and antimicrobial proteins
Recognizes a wide spectrum of pathogens without a need for prior exposure
Key players include neutrophils, monocytes, and macrophages
These cells phagocytose pathogens and trigger the cytokine and chemokine network
can lead to inflammation and specific immune response
Except for Erythrocytes (Which are red cells) the rest are white cells.
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
2.) Agranulocytes (Mononuclear leukocytes)
A.) Macrophages
Monocytes mature into active macrophages at site of infection
Intracellular killing and digest pathogens via phagocytosis
Phagosome fuses lysosome, (oxygen-containing and nitrogen-containing free radicals)
Roam continuously in the extracellular fluid bathing tissues
Antigen-presenting cell (APC) for helper T cells (TH)
Respiratory burst for additional cell-killing ability (liberates deluge of free radicals
Express Fc receptor molecules for IgG to trap antigen-antibody complexes
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
3.) Granulocytes (polymorphonuclear leukocytes)
A.) Neutrophils
Most abundent circulation leukocytes (50-70% of peripheral blood leukocytes)
Frst cell on site of tissue damage or infection
Intracellular killing via phagocytosis, greater range of reactive oxygen radicals
Large numbers in blood until attracted to tissues during inflammation
Roam in the extracellular fluid bathing tissue
B.) Eosinophils
2%-5% of total leukocytes in blood
Important in the elimination of parasites
Degranulation, next to parasite, releases extremely potent mediators (enzymes & toxins)
High blood count is often associated with parasitic infection & allergic diseases
Express Fc receptor molecules for IgE
C.) Basophils
Ciculating cells, least numerous at about .5%
Not important as phagocytes
Release mediators such as histamine to promote inflammation
Express Fc receptor molecules for IgE
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
Lymphocytes
Natural Killers (NK) Cells
Do not kill pathogen directly, but induce apoptosis of infected cells (Cancer and Viral)
Release perforins, insert in membrane and make pores, granzymes enter infected cell and activate capase enzymes that induce apoptosis
Big player in immune surveillance and the bodies defense against cancer
Do not have T-cell receptors, but do express Fc receptor for IgE
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
Mast Cells
Primarily located under mucosal surfaces
Release chemical mediators such as histamine to promote inflammation
Triggered during allergic responses
Express Fc receptor molecules for IgE
Important component of the inflammatory response
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
Acute inflammation
Occurs over seconds, minutes, hours and days
Chemical Signals are released by infected or injured cells during inital response to tissue damage (acute phase).
Dilation of local blood vessels increases blood flow at site (red & warm)
Increase permeability of capillaries causing edema (tissue swelling)
Tissue swelling puts pressure on nerve endings (pain & potential loss of function)
Macrophages and neutrophils release cytokines interleukin-1 (IL-1) and tumor necrosis factor (TNF) which acts on hypothalamus to raise body temp. (fever)
Fever is one of the most common symptoms of infection
Fever stimulates phagocytosis and causes liver and spleen to store iron and zinc needed by bacteria
Fever may destabilize certain viruses and bacteria
5.) Cell death (necrosis) always occurs to some degree during inflammation
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
Immediate Hypersensitivity
A type of ANTIBODY-MEDIATED immunity which involves degranulation of basophils and mast cells in the area
Basophils and mast cells have receptors that bind the Fc portions of antibody (IgE)
When exposed to the same allergen a 2nd time, degranulation occurs
Results in dilation of local blood vessels and increased permeability; edema
Immediate hypersensitivity is important in some parasitic infections
Immediate hypersensitivity in humans is the bases of allergies and asthma
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
Anaphylaxis (Systematic immediate hypersensitivity)
hypersensitivity produced by exposure to further doses of the same protein, usually when exposure is within less than 2 weeks
Basophils and mast cells release pharmacologically active substances
Widespread rapid inflammatory responses that may be fatal f not treated rapidly
Tremendous drop in blood pressure.
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
Chronic Inflammation
Acute inflammation that fails to heal; occurs over longer times and is disease related
Fibrosis: arise from abnormal and continuous wound repair processes that fails to terminate resulting in elevated levels of collagen and scarring
Granulomas: Nodules of inflammatory tissue that may accumulate around persistent antigen
Abscess: When necrotic debris confined to a localized area forms pus that may cause an increase in hydro-static pressure
Ulcers: An area of inflammation that opens out to a skin or mucous surface
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
A comlement and iterferons
A. Complement
Consists of approx. 30 different proteins
Circulate freely in blood plasma, generally in inactive form (Zymogen)
Complement can be activated by classical pathway (antigen-antibody complex) or alternative pathway (spontaneously) or lectin pathway (cell wall polysaccharides of certain bacteria and fungi)
Complement proteins (C3b) coat pathogen surface (opsonization), thus promoting phagocytosis and destruction of pathogen by macrophages and neutrophils which have receptors for C3b
C5a is an important chemotactic protein, helping recruit inflammatory cells
Complements C5b initiates pathway for membrane attack complex
B. Intererons (IFN-A, IFN-B, IFN-y)
A class of proteins synthesized upon parasitic infection of a cell
Acts as messengers to protect normal cells in vicinity from becoming infected
IFN-A and IFN-B include the degradation of RNA and block protein production
IFN-y is produced by TH cells and natural killer cells to stimulate cells in the cellular response
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
Cytokines and Cell signaling
A. Cytokines
Cytokines are protein hormones utilized by immune cells to communicate
Can effect same cells that produce them, cell nearby, or cells distant in the body
B. Cell signaling
Ligand binds to a specific cell receptor protein initiating intracellular signal cascades
Ligands may be located on cell surface of neighboring cells, dissolved in blood (Cytokines) or on the surface of or secreted by pathogens
Cascades may activate transcription factors or proteins that control gene induction, cell death, and secretion
JACK-STAT pathway: 3 main components include:
Receptor
Janus Kinase (JAK)
Signal Transducer and Activator of Transcription (STAT)
Transmembrane receptor, activated by cytokine
Activates the JAK protein, which adds phosphate groups (P) to the receptor
Kinases: Proteins that add phosphate groups to othe proteins
Phosphate groups: act as an “on” and “off” switch on proteins
STAT is recruited and itself becomes phosphorylated forms dimer, and moves into the cell nucleus, where it binds to DNA promoter region.
II. Nonspecific immunity (Innate Immunity)
The Second line of defense
Pattern Recognition Receptors
Receptors with broad specificity that bind to molecules on the surface of pathogens; stimulated by PAMPs
Pathogen-Associated molecular patterns (PAMP): A small molecular motifs conserved within a class of pathogens
Scavenger Receptors: Bind lipoproteins and lipopolysaccharides from bacterial cells including Gram-Positive
Complement Receptors: Integral membrane proteins that recognize fragments of complement and mediate various defense functions, including phagocytosis
Toll-Like Receptors (TLRs): Single, membrane-spanning, receptors that recognize structurally conserved molecules of carbohydrates, nucleotides, and proteins derived from viruses, bacteria, protozoa, and helminthes parasites.
III Acquired Immunity:
Third Line of defense
Four important aspects of immune response include:
Nonself recognition:ability to distinguish self-antigens from nonself
Anti-gen Specific: Recognizes and is directed against specific antigens
Systemic Response: Immunity is not restricted to initial infection site
Memory: Recognizes and mounts stronger attack on previously encountered pathogens
III Acquired Immunity:
Third Line of defense
Basis of self and non-self recognition
Major Histocompatibility Complex (MHC): Cell surface glycoproteins, highly polymorphic
MHC Class I Proteins
Present on every nucleated cell of the body (few exceptions)
Cytotoxic T cells (CD8) respond to endogenous antigen bound to MHC Class I proteins
MHC Class II Proteins
Found only on antigen presenting cells (macrophages, B cells, and dendritic cells)
TH cells (CD4) respond to exogenous antigen bound to MHC Class II proteins
III Acquired Immunity:
Third Line of defense
Two seperate but overlapping arms of immunity
Cell-mediated Immunity: Entirely associated with cell surfaces, T-cell receptors, that are unable to “see” free antigens
T Cells: Can regulate the immune responses of other cells (CD4) or indirectly kill cells (CD8) that carry specific antigens
Lymphocytes produced in red bone marrow, migrate to thymus (primarly lymphoid organ) where they mature (VDJ recombination of T cell receptors) and undergo selection
T-cell receptors must recognize self MHC proteins needed for activation, but not the self antigens (self tolerance) that the MHC presents (T-cell eliminated in thymus if criteria not met)
“Naive” T cells recirculate only between blood and lymphoid organ (Ex. Spleen, tonsils, or lymph nodes)
T-cell receptors re transmembrane proteins with constant and variable region, like antibodies:; composed of 2 chains (alpha and beta)
T-Cell receptors recognize only a processed peptide fragment that the APC’s MHC presents to the T-cell receptor, unlike B-cell receptors
Other transmembrane proteins closely linked to T-cell receptors serve as coreceptors, such as CD4 and CD8
T Cell activation occurs in secondary lymphoid tissue when antigen is displayed with self MHC on mature dendritics cells (DCs)
III Acquired Immunity:
Third Line of defense
Cytotoxic T Cells
Kill cells that are infected with viruses (or other pathogens)
Have CD8 coreceptor protein
Antigen-presenting cell (APC) often include dendritic cells (professional APC)
Activated by endogenous antigens bound to MHC class I proteins of dendritic cells
Activation results in the release of IL-2, TNF, and IFN-y; and they differentiate into memory cells and activated cells (clonal expansion)
“altered -self” cells expressing the same combination of foreign peptide on MHC cless I are targeted; may include tumor cells, virally infected cells, or cells with intracellular parasites
Relase perforins, insert in membrean and make pores, granzymes enter infected cell and activate caspase enzymes that induce apoptosis
III Acquired Immunity:
Third Line of defense
Helper T Cells
Involved in activating and directing other immune cells; their cytokines larger determine whether an immune response is humoral or cell-mediated; not killing ability
Have CD4 corecpetor protein
1st signal is initiated by exogenous antigens bound to MHC class II proteins of macrophages, dendritic cells (phagocytosis or endocytosis), and B cells (receptor-mediated endocytosis)
2nd signal is a verification step, naive TH cells express the protein CD28 that must bind to costimulatory B7 protein on professional level
When 2nd activation signal is complete the originally undetermined T-Helper null cell (TH0) releases a potent T cell growth factor celled interleuin 2 (IL-2) which activates the T-cell’s proliferation pathways
TH0 cells differentiate into TH1 or TH2 cells depending cytokine environment Cellular Response- IL-12 & IFN-y induces TH1 differentiation; IFN-y inhibits TH2 cells Humoral Rsponses- IL-4 drives TH2 differentiation, and inhibits TH1 cell production
Both T helper cells group are able to inhibit the activation of the other group using their own cytokines
TH1 Cells communicate attack against intracellular bacteria and protoza
TH2 cells communicate attack against extracellular parasites including helminths
TH1 Cells mainly secrete
IL-2
IFN-y
TNF
GM-CSF
TH2 Cells mainly secrete
IL-4
IL-5
IL-10
III Acquired Immunity:
Third Line of defense
Humoral Immunity
Based on antibodies on cell surfaces and in body fluids (blood, lymph, etc)
III Acquired Immunity:
Third Line of defense
B Cells
Bind specific to free (soluble) antigen or particulate antigen with its membrane bound antibody (B cell receptors); also serves as APC to TH cells
B cells produce in red bone marrow; immunoglobulin (Ig) synthesis occurs
Ig is encoded by different segments of DNA, a V (vaiable) segment, a D (diveristy) segment, a J (joining) segment, and a constant region; variable regions are shuffled by RAGs
Each Ig consists of 2 identical short polypeptides called light chains and 2 identical longer polypeptides chains called heavy chains; held together by disulfide bonds to form a Y-shaped molecule
Each “arm” is called FAB (fragment antigen-binding) region and the “stem” is called Fc (Fragment crystalization)
Immunoglobins IgM (monomeric form) and IgD are present on mature “naive” B cells
B cell recirculate only between blood and lymphoid organs, activated in secondary lymphiod organ
B cells recognize their cognate antigen in its native form with its B-cell receptors (atibodies); each Ig can bind 2 identical epitopes
Binding of antigen to Ig on surface o appropriate B cell is usually not sufficient to activate the B cell to multiply; so, B cell (APC) internaizes antigen-antibody complex and incorporates portions of antigen (epitope) on MHC II
Specific TH2 Cells recognizes antigen displayed by B cell; cytokinesis
Plasma B-cells: Are large B cells that have been exposed to antigen
Produce and secrete large amounts of antibodies
Short lived die after threat is eliminated
Memory B cells: Specific to antigen encountered during primary immune response
Can espond quickly should the threat re-appear
Long lived cells
Each B cell can only produce antibodies attacking a specific antigen.
IGM: Pentamer, 1st antibody secreted during primary immune response; monomer, present on surface of B cells
IgG: Monomer, major antibody secreted during the secondary response; 75% of plasma antibodies
IgD: Monomer, present only on surface of B cells; serves as antigen receptor
IgA: Dimer, most abundant form of antibody in body secretions; high density of IgA-secreting plasma cells in MALT
IgE: Fc binds to mast cells, basophils, etc; often secreted in response to helith worms
Human immunodeficiency Virus (HIV)
A retrovirus that attacks the body’s immune system; caused by AIDS
HIV mounts direct attack on TH cells and binding to CD4 proteins on cell surface; monocytes are infected
Platyhelminthes (flatworms)
Phylum containing simplest bilaterally symmetrical animals
Most are parasitic
Acoelomate body plan (No body cavity other than the gut); rarely has anus
Tripoblastic (Composed of three fundamental cell layers)
Doroventrally flattened (greater surface area to respire by diffusion)
Tegument (surficial covering of a multicellular organism, an intergument)
Parrnchyma (Loosely arranged mass of fibers and cells of several types)
Digenetic Trematodes (Flukes)
A subclass within the class trematoda
Body Form (flukes)
Most are dorsoventrally flattened and oval in shape; others as thick as they are wide
Length ranges from 1.0mm to 6.0cm
Oral Sucker: Muscular sucker that surrounds the mouth
Acetubulum: Ventral sucker of a fluke
Distome: Fluke with two suckers, oral and ventral
Monostome: Fluke that lacks a ventral sucker
Amphistome: Fluke with the ventral sucker located at the posterior end
Tegument
Surficial covering of a multicellular organism, an integument
Distal Cystoplasm: Anucleate layer of cytoplasm above a”Sunken epidermis”
Cytons: Cell bodies containing nuclei; lie below the superficial muscle layers
Internuncial processes: channels that connect cytons to distal cytoplasm
Syncytial: Describes the continuous distal cytoplasm with no intervening cell membranes
Spines: Consist of crystalline actin; often present in certain areas of the tegument
Spines lie above the basement membrane of the tegument