Microbiology CH17 Adaptive Immunity pt1

adaptive immunity

defenses that target a specific pathogen after exposure

adaptive immunity characteristics (3)

- distinguish self from nonself

- active when innate defenses fail to stop microbe

- acquired through infection or vaccination

primary response

first time the immune system combats a particular foreign substance

secondary response

later interactions with the same foreign substance; faster & more effective due to "memory"

2 natures of adaptive immune system

- humoral immunity

- cellular immunity

humoral immunity

prod. antibodies that combat foreign molecules

humoral immunity antibodies

B cells

humoral immunity B cells charcateristics (3)

- lymphocytes

- created & mature in Bone marrow

- recognize antigens & make antibodies

cellular immunity (cell-mediated immunity)

prod. t lymphocytes which recognize antigenic peptides processed by phagocytic cells

cellular immunity t lymphocytes characteristics

- mature in Thymus

- have t cell receptors (TCRs) on t cell surface

TCRs (t cell receptors) function

contact antigens, causing t cells to screte cytokines instead of antibodies

cellular immunity vs humoral immunity

- cellular immunity attacks antigens that have ALREADY entered cells

- humoral immunity fights invaders & threats OUTSIDE cells

Cytokines

chemical messengers prod. in response to a stimulus

Types of cytokines (5)

- interleukins

- chemokines

- interferons

- tumor necrosis factor alpha (TNF-a)

- hematopoietic cytokines

interleukins

cytokines between leukocytes

chemokines

induce migration of leukocytes

interferons

interfere with the viral infections of host cells

tumor necrosis factor alpha (TNF-a)

involved in the inflammation of autoimmune diseases

hematopoietic cytokines

control stem cells that develop into red & white blood cells

Cytokine storm

overproduction of cytokines

antigens

substances that cause the prod. of antibodies

epitopes/antigenic determinant

specific regions on the antigen where antibodies interact with

antigen characteristics (7)

- components of invading microbes

- capsules

- cell walls

- flagella

- fimbriae

- toxins

- viral capsids

- viral spikes

nonmicrobial antigens (3)

- egg white

- pollen

- cell surface molecules

Haptens

molecules too small to be antigenic; attach to carrier molecules & provoke an immune response

Humoral immunity antibodies

immunoglobulins (compact soluble proteins)

humoral immunity immunoglobulin

recognize & bind to specific antigens, targeting them for destruction

valence

# of antigen-binding sites on an antibody (bivalent antibody = 2 binding sites)

humoral immunity antibody structure

- 4 protein chains in a Y shape (2 identical light chains & 2 identical heavy chains joined by disulfide links)

humoral immunity antibody structure regions

- variable (v) regions at the ends of the arms (bind epitopes)

- constant (Fc) region is the stem (identical for a particular Ig class)

types of humoral immunity antibodies (5)

- IgG

- IgM

- IgA

- IgD

- IgE

IgG (3)

- monomer

- in blood, lymph, intestine

- 80% of serum antibodies

IgG actions (4)

- cross placenta & protect fetus

- trigger complement activation

- enhance phagocytosis

- neutralize toxins & viruses

IgM (4)

- pentamer (5 monomers held with a J chain)

- valence of 10 (pentamer valence=10)

- 6% of serum antibodies

- remains in blood vessels

IgM actions (3)

- causes agglutination (clumping) of cells & viruses

- activates complement

- released as first response to an infection (short lived)

IgA (3)

- monomer in serum; dimer in secretions

- 13% of serum antibodies

- in mucous membranes, saliva, tears, breast milk

IgA action

prevent microbial attachment to mucous membranes

IgD (4)

- monomer

- .02% of serum antibodies

- similar structure to IgG

- in blood, lymph, on B cells

IgD action (2)

- no well-defined action

- may play a role as membrane immunoglobin on B cells

IgE (3)

- monomer

- .002% of serum antibodies

- on mast cells, basophils, in blood

IgE actions (2)

- release histamine when bound to antigen; lysis of parasitic worms

- important role in Type I hypersensitivity reactions (allergies)

activation of antibody producing cells

antigen-presenting cells must display antigen on their surface in association with major histocompatibility complex (MHC) class II protein

MHC (major histocompatibility complex)

genes encode molecules on the cell surface

types of MHC (2)

- Class I

- Class II

Class I MHC (2)

- on membrane of nucleated cells

- identifies a cell as "self"

Class II MHC

- on the surface of antigen-presenting cells (APCs) (b cells, macrophages, dendritic cells)

inactive B cells process with antigens (3)

- contain surface Ig that bind to antigen

- internalizes & processes antigen

- antigen fragments displayed on MHC class II molecules

T helper cells

contacts the displayed antigen fragment & releases cytokines that activate B cells (activating clonal expression (proliferation of B cell))

clonal expansion and differentiation

differentiate activated B cells into:

- antibody-producing plasmacytes

- memory cells

clonal deletion

elims. harmful B cells

t-dependent antigen

antigen that requires a t helper cell to prod. antibodies

t-independent antigens (3)

- stim. the b cell w/o help of t cells

- provoke a weak immune response (usually prod. IgM)

- NO MEMORY cells generated

diversity of antibodies (2)

- 100 billion dif. antibodies can be made by one indivudal

- immuunoglobulin genes have segmenta that rearrange to prod. diversity in the antigen-binding section of antibody molecule

antigen-antibody complex (function & location) (2)

- forms when antibodies bind to antigens

- prot. the host by tagging foreign molecules or cells for destruction

affinity

strength of the antigen-antibody complex bond

methods of protection via antigen-antibody complex (5)

- agglutination

- opsonization

- antibody-dependent cell-mediated cytotoxicity

- neutralization

- activation of the complement system

t cells function

combat intracellular pathogens & abnormal host cells (cancer)

t cells characteristics (4)

- mature in thymus

- thymic selection: elim. immature & self-reactive t cells

- migrate from thymus to lymphoid tissues

- attach to antigens via t-cell receptors (TCRs)

pathogens entering gastrointestinal tract... (route)

pass through microfold (M cells) located over Peyer's patches (aggregated lymphoid nodules)

pathogens entering gastrointestinal tract (purpose)

transfer antigens to lymphocytes & antigen-presenting cells (APCs)

types of APCs (2)

- dendritic cells (DCs)

- macrophages

dendritic cells (2)

- engulf and degrade microbes & display them to T cells

- found in the skin, genital tract, lymph nodes, spleen, thymus, & blood

macrophages (2)

- activated by cytokines or the ingestion of antigenic material

- migrate to the lymph tissue, presenting antigen to T cells