ch15 - adaptive immune response, unfinished

strategy of the adaptive immune response

first response to an antigen → primary response

• may take a week or more to develop

immune system remembers pathogen on subsequent exposure → secondary response

• gets rid of the pathogen before you even know you encountered it

• vaccine exploits phenomenon of immunologic memory

• for long term protection, very important: memory B cells will differentiate into plasma cells → rapid production of antibodies

strategy of the adaptive immune response - humoral and cell-mediated immunity*

adaptive (acquired) immunity divided into

• humoral immunity

  • eliminates extracellular pathogens

  • mediated by B cells

    • mature in bone marrow

    • *some become plasma (b?) cells that produce antibodies

    • some become memory cells

      • allows rapid secondary response if encounter antigen again

• cell-mediated immunity

  • eliminates intracellular pathogens

  • mediated by T cells

    • mature in thymus

    • cytotoxic T cells, helper T cells, regulatory T cells (suppressor T cells)

• for every T cell that is stimulated by a specific antigen, there’s a B cell that produces specific antibodies

overview of the adaptive immune response

both parts work together to produce a strong immune response

the nature of antigens

antigen

• antibody or generator

• any compounds that elicit an immune response (immunogen) → antibody production

epitopes

• antigenic determinants on surface of microbes that trigger response

• macromolecules

  • proteins, lipids, and polysaccharides

the nature of antibodies

antibodies also called immunoglobulins

• structure

  • four chains of amino acids held together by disulfide bonds

  • Y-shaped proteins with two general parts

    • constant region (Fc region)

    • variable region (Fab)

      • unique to each Ab

      • recognizes and binds to a specific Ag

the nature of antibodies - protective outcomes of antibody-antigen binding

neutralization

• prevents toxins, viruses from binding

immobilization and prevention of adherence

• binding to bacterial flagella or pili

cross-linking

• clumping of bacterial cells by specific antibody

• enhances phagocytosis

opsonization

• enhances phagocytosis

the nature of antibodies - Ab divided into 5 classes

based on constant region of the antibody

• IgM

• IgG

• IgA

• IgD

• IgE

five classes of antibodies - IgM

• pentamer

• first Ab produced in primary response to infection

• more forgiving (recognition is less specific)

• only Ab that can be formed by the fetus

five classes of antibodies - IgG

• second to be produced

• most protective and most specific

• most abundant Ab in blood (80-85%) and long lasting

• only Ab that can cross the placenta and found breast milk

  • last 6 months to several in child

• the antibody of memory ⭐

five classes of antibodies - IgA

• most form dimer

• found in secretions, important in mucosal immunity

• found in breast milk, mucus, tears, and saliva

five classes of antibodies - IgD

• help in maturation of antibody response (IgG)

• function well not understood

five classes of antibodies - IgE

• barely detectable in circulation

• active in allergic reaction → produces histamines

• tightly bound via Fc region to basophils and mast cells

  • allows these cells to detect, respond to antigens

clonal selection and expansion of lymphocytes

antigen in body → antibody production

• process called clonal selection

  • B cell bind antigen, divides and

    • differentiate into plasma cells → produce lots of antibodies

    • become memory cells

      • responsible for secondary response

without sustained stimulation, cells undergo apoptosis

The B-Cell Response: Humoral Immunity

Primary Response

• occur after first encounter with antigen

• takes 10-14 days for substantial antibody accumulation

  • activated B cells divides and become plasma cells as long as antigen is present

  • net result = increase in antibody titer

Secondary Response

• occurs after subsequent exposures

• fast, more effective response due to memory cells

  • pathogens usually eliminated before causing harm

• vaccine exploits this natural phenomenon of immunologic memory

T Cell Response: Cell-Mediated Immunity

involves T cells

• two types: cytotoxic T cells and helper T cells

• interact directly with target cells

• never produce antibodies

Two major T cell populations - Cytotoxic T Cells

have CD8 marker

activated by dendritic cells

recognize antigen display by MHC class I cells (all nucleated cells)

• release of proteases and perforin to induce apoptosis

destroy infected or cancerous “self” cells

Two major T cell populations - Helper T Cells

have CD4 marker

recognize antigen presented on MHC class II from antigen-presenting cells (APCs)

orchestrate immune response

• activate B cells and macrophages

• stimulate other T cells

Natural Killer (NK) Cells

induce apoptosis in abnormal “self” cells

• recognize foreign proteins on cell membrane bound by antibodies

  • bind, deliver perforin - and protease - containing granules to cell, initiating apoptosis

• also recognize host cells lacking MHC class I

  • some viruses interfere with antigen presentation