Ch. 12 & 13 - Host Defense

immunology

the study of host defenses, defending against which is foreign; the branch of science that deals with the response of an organism to antigenic challenge and its recognition of what is self and what is not

foreign matters of immunology include:

bacteria, viruses, viroids, satellite, prions, malignant cells, transplants, and transfused fluid

innate (natural) immunity

the nonspecific defenses that attack foreign material, activates immediately upon exposure, response is same with each encounter of invader

acquired (adaptive) immunity

the specific defenses that develop to specific foreign material, cell memory involved, response is quicker & stronger with each encounter of same antigen

what is a healthy functioning immune system responsible for?

surveillance of the body, recognition of foreign material, distinguishing self from non-self, destruction of foreign/non-self

what must immune cells be able to do?

immune cells must be able to distinguish self cells from non-self cells and respond at an appropriate level

what can be damaging to the host?

responding to self cells can be damaging to the host

when can autoimmunity result?

autoimmunity can result when the body cannot distinguish self from non-self

what is an example of an autoimmune disease?

rheumatoid arthritis

what do self cells have present on all nucleates cells?

markers (major histocompatibility complex molecules)

what types of markers do non self cells have?

pathogen associated molecular patterns (PAMPs) or microbe associated molecular patterns (MAMPs)

pattern recognition receptors (PRRs)

found on host cells bind to these markers, determine if an immune response is necessary to what extent should the response be

what do immune systems consist of?

various cells, tissues, and organs

arrangement of immune system

large, complex, diffuse network of cells tissues, organs and fluids that exist throughout the body

what does the arrangement of the immune system promote?

this arrangement promotes surveillance and recognition processes that help screen the body for harmful substances

leukocytes

white blood cells, originate in bone marrow, start as pluripotent stem cells, some white blood cells reside in blood and some reside in tissue, detect pathogens by MAMPs/PAMPs

what are white blood cells categorized as?

agranulocytes or granulocytes

granules

vasoactive molecules stored in vacuoles near cell membrane, released when stimulated by presence of foreign material

mast cells

type of granulocytic WBC found in tissues, do not circulate, trigger local inflammatory and allergic responses

neutrophils

phagocytic granulocyte, short-lived cell, circulate in blood, migrate to tissue

basophils

type of granulocytic WBC that functions in inflammatory and allergy responses

eosinophils

granulocyte that circulates in bloodstream, functions in inflammation, important in parasitic infections like protozoans and helminths

monocytes

agranulocyte that circulates in bloodstream and develops into dendritic cells or macrophages

macrophages

agaranulocytes that function in phagocytosis, derived from monocytes

what tissues do macrophages reside in?

liver (kupffer cells), lungs (alveolar macrophages), skin (langerhans cells), brain (microglia)

dendritic cells

agranulocyte with long extensions, resemble dendrites of nerve cells, derived from monocytes, bridge innate/acquired immunity, process foreign matter

lymphocytes

non-phagocytic cells, found in blood and lymph, major part of adaptive immunity

b lymphocytes (B cells)

originate and mature in bone marrow, differentiate into plasma cells, produce antibody

t lymphocytes (T cells)

originate in bone marrow, mature in the thymus, can directly kill cells (nature killer T cells and t cytotoxic cells), can help other immune cells (t helper cells)

platelets

function in blood clotting and inflammation, plays a role in destruction of blood-borne pathogens

red blood cells

transport oxygen and carbon dioxide for proper cellular functions

primary lymphatic organs & tissues

sites where immature lymphocytes mature

thymus

naive immature lymphocytes mature into T cells, removes T cells reactive against self

bone marrow

site of blood cell production, where immature lymphocytes mature into B cells

secondary lymphatic organs & tissues

where lymphocytes encounter Ag, become activated

spleen

filters blood, traps & removes blood-borne particles, removes old, worn RBC from circulation

lymphatics

lymphatic system is a compartmentalized network of vessels, cells, specialized accessory organs which transports lymph through vessels & nodes, leading to major vessels that drain back to circulatory system

lymph

fluid carried by lymphatic circulation, bathe cells & tissues, contains WBC & lymphocytes

lymph vessels

transport lymph, flowing in the direction towards the heart form extremities

lymph nodes

small bean-shaped organs, site of lymph filtration, removal of foreign material

what are some host defenses closely related to specific tissue?

SALT, MALT, GALT, BALT

tonsils in the pharynx are…

rings of tissues that provides a source of lymphocytes

what are peyer’s patches?

peyer’s patches in the intestines & appendix also provide protection

skin associated lymphoid tissue (SALT)

contains specialized cells, langerhans cells, dendritic cell that can phagocytose antigens, presents antigen to and activates T cells

mucosal-associated lymphoid tissue (MALT)

gut-associated lymphoid tissue (GALT), bronchial-associated lymphoid tissue (BALT), urogenital system MALT

what are physical mediators of defense’s effectiveness impacted by?

direct and indirect factors, along with host’s secretions (flushing), barriers are first line of defense

skin

effective mechanical barrier that thick, tough, highly impervious, waterproof; outer layer of keratinized epithelium, microbiota reside, constant sloughing of skin takes potential pathogens with it, sweat has low pH and flushed away microbes

mucous membranes

skin modification near internal structures, found several places on body like eye nose and mouth, each location has its own microbiota, slippery in nature, flushed out microbes, traps invaders, produces enzymes like lysozymes or proteins like lactoferrin that are anti-microbial

respiratory system

hairs and cilia trap microbes, mucous lined, coughing, sneezing, salivation

gastrointestinal tract

stomach pH 2-3, intestines have enzymes and peristalsis intestinal microbiota

genitourinary tract

flushing action physically removes pathogen, low pH, microbiota, mucous membranes, enzymes present

lysozymes

enzymes found in secretions such as sweat, tears, saliva; breaks down peptidoglycan by breaking bond between NAG-NAM

cytokines

cell phone of immune system, proteins releases by cells in response to certain stimuli that act as intercellular signalers, mediators

histamines

vasodilators/vasoconstricters act to change diameter, permeability of blood vessels; produced my mast cells and basophils

interleukins

IL-1,IL-7,IL-10; have roles in inflammation and regulation of immune responses

interferon (IFN)

proteins produced by WBC, tissue cells that defend against microbes, in particular viruses; induces change in genetic expression

defensin

small peptide with antimicrobial activity; can insert into bacterial membranes, disrupting membrane integrity

complement

plasma proteins found in blood, act in cascading fashion to “complement” other host defenses; phagocytosis enhanced (opsonization) by tagging foreign material &/or attacking it outright

what are 3 ways to activate complement cascade?

classical pathway (Ag/Ab complex), lectin pathway (protein bound to specific CHO), alternative pathway (repetitive structures)

phagocytosis

form of endocytosis, cells ingest large particles into membrane-bound vesicles called phagosomes, degraded by lysosomes

professional phagocytes

macrophages, neutrophils, dendritic cells

process of phagocytosis

chemotaxis and adhesion, engulfment and phagosome formation, phagolysosome formation & killing and destruction

chemotaxis and adhesion

phagocytes drawn to foreign matter, directed by chemokines, use PRRs to recognize PAMPs on foreign cells and bind it

engulfment and phagosome formation

once bound, phagocyte extends cell membrane pseudopods, enclose prey in a pocket, internalize in vacuole (phagosome)

pahgolysosome formation, killing & destruction

lysosome, migrate to, fuse with phagosome (phagolsyosome), granules released into phagolysosme, digesting foreign material

inflammation

natural nonspecific protective response to injury/destruction/infection which blocks spread of infectious agent, helps reduce further host damage

what are the goals of inflammation?

to mobilize immune responses to the site of injury, to mobilize repair mechanisms to heal injury, clear away harmful substances and destroy microbes, prevent further invasion

how long does acute inflammation last?

acute inflammation lasts days to weeks, usually ending in tissue repair

how long does chronic inflammation last?

chronic inflammation leads to progressive changes, causing permanent tissue damage, scar tissue

cardinal signs of inflammatory response

redness, warmth, pain, swelling, altered function

redness

rubor; vasodilation, increased circulation in injured tissues

warmth

calor; heat given off by the increased flood flow

pain

dolor; stimulation of nerve endings

swelling

tumor; increased fluid escaping into the tissues

altered function

functio lease; loss of function

stages of inflammation

chemotaxis & diapedesis, edema & pus formation, AND resolution, repair, and scar formation

chemotaxis & diapedesis

Changes occur in blood vessels in the vicinity of damaged tissue, Chemical mediators (cytokines, chemokines) released by blood cells, tissue cells, platelets near injury, summoning immune cell responses (chemotaxis), WBC in blood vessels summoned to tissues, cells pass through blood vessels, migrate to tissues (diapedesis), follow chemokine signals to the site of injury/infection, Vascular reactions include sequences of dilation & constriction of vessels near injury, pushing foreign material from the area, bring more blood to the area, eRedness & warmth associated with inflammation

edema & pus formation

edema results with influx of fluids into tissues causing swelling and hardness to the area; fluids contain various plasma proteins, blood cells, cellular debris; fluid may be fairly clear (serous) or contain RBC or pus, some microorganisms are pyogenic (pus-forming) like streptococcus and staphylococcus; influx of fluids also dilutes any toxic material that may be present; fibrin creates clots that traps microbes to prevent infection spread

pus

thick white-yellowish fluid, composed of dead/dying WBC (mostly neutrophils), dead tissue, dead microbes

resolution, repair, scar formation

complete repair and return to normal healthy status OR formation of scar tissue

fever

Abnormally elevated body temperature, symptom of infection, Body temperature maintained around 37°C (98.6°F) by the hypothalamus

low-grade fever

37.7 to 38.3C or 100 to 101F

high-grade fever

40.0 to 41.4C or 104 to 106F

when is fever initiated?

fever initiated when substances (pyrogens) re-set body thermostat higher

endogenous pyrogens

originate from inside the body, are released by cells during phagocytosis

exogenous pyrogens

come from outside the body, including viruses, bacteria, protozoa, fungi, endotoxins, blood, and vaccines

benefits of fever

inhibits multiplication of temperature-sensitive microorganisms, interferes with nutrition of bacteria by reducing the availability of iron, increases metabolism and stimulates immune reactions and naturally protective physiological processes