BIO205 - Chapter 15: Adaptive Immunity

adaptive immunity

• lymphocytes recognize foreign materials (antigens) and proliferate, leading to adaptive immunity

immunological memory

stronger response to re-exposure, vaccination relies upon this ability

immune tolerance

must distinguish between “healthy self” and “dangerous”

cell mediated immunity (CMI)

• deals with invaders

• relies on T lymphocytes

• cytotoxic T cells induce apoptosis in self cells infected with viruses

• helper T cells direct and assist various immune responses

humoral immunity

• eliminates microbial invaders and toxins in the blood or tissue fluids

• involves B lymphocyte (develop in bone marrow)

  • programmed to produce Y-shaped proteins called antibodies

  • these bind to specific antigens, making them as an invader to be eliminated

lymphocytes

T and B cells

• can go through several stages of development

• mature when cells have specific receptor proteins on surface

• at this stage cells are immunocompetent

T lymphocytes

mature in the thymus

• cytotoxic and help T cells

• TRC does not recognize free antigen

  • antigen must be presented by body’s own cells

cytotoxic T cells

respond to endogenous antigens presented on MHC class I molecules

helper T cells

respond to exogenous antigens presented on MHC class II molecules

regulatory T cells

role is to prevent immune system from mounting a response against “self” molecules

B lymphocytes

B cells that form in the bone marrow

• differentiate into plasma cells

• produce Y shaped proteins called antibodies

  • antibodies bind to antigens with high degree of specificity

  • some are long-lived and form memory B cells

primary lymphoid organs

where lymphocytes develop

examples: bone marrow and thymus

secondary lymphoid organs

sites where lymphocytes gather to encounter antigens

examples: lymph nodes, spleen, tonsils, adenoids, appendix

T Cell receptors (TCR’s)

only bind an antigen “presented” by one of the body’s own cell, binding is guided by a surface molecule called a CD marker

• Cytotoxic T cells have CD8

• Helper T cells have CD4

B Cell Receptors (BCR’s)

membrane-anchored antibodies

• bind free antigens

• two arms of BCR are identical to each other, resulting in two antigen-binding sites

Class I MHC proteins

found on all cells in the body

Class II MHC proteins

found only on a few types of cells such as macrophages, B-cells

antigens

come from antibody generator

• elicit immune response called immunogen

• proteins and polysaccharides

antigens contain multiple antigenic determinants (epitopes)

T-dependent antigens

for most antigens B-cell requires signal from helper T-cell

T-independent antigens

can activate B cells without aid

IgM antibodies

first Ab to respond to infection

• 5-13% of antibodies in circulation

• agglutinates microbes

PENTAMER

• only antibody that can be formed by the fetus

IgG antibodies

dominant antibody in circulation

• 80-85% of antibodies in circulation

• enhances phagocytosis

only antibody that can cross the placenta

MONOMER

IgA antibodies

found in secretions

• 10-13% of antibodies in circulation

• breast milk, mucous, tears, saliva

MONOMER IN SERUM

DIMER IN SECRETIONS

IgD antibodies

less than 1% of serum immunoglobulins

• involved with development and maturation of antibody response

• function in serum, not really defined

MONOMER

IgE antibodies

antigen binds to two adjacent IgE molecules carried by mast cells and basophils, cell releases histamine and other inflammatory mediators

• basophils and mast cells also release chemicals when IgE binds to normally harmless foods, ducts, pollen, yielding allergic reactions

MONOMER

Natural Killer (NK) cells

induce apoptosis in “self” cells

• NK cells recognize host cells with foreign proteins in membrane bound antibodies

• NK cells 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