Immunity

· immune system produces antibodies against foreign agents

· immune system remembers

· second exposure to foreign agent evokes greater and more rapid response

· two types of immunity

· humoral

· cellular

Development

· lymphocyte precursors come from bone marrow

· migrate to modifying organ

· then return to lymph nodes and bone marrow

T cells

· lymphocytes that populate thymus become T lymphocytes

· mediate cellular immunity

· differentiate into four types

· helper/inducer T cells

· suppressor T cells

· cytotoxic T cells

· memory T cells

· helper/inducer and suppressor cells involved with regulation of antibody production by B cells

· cytotoxic cells destroy foreign cells

· helper/inducer cells called T₄ cells

· cytotoxic and suppressor cells called T₈ cells

B cells

· those that populate spleen and liver become B lymphocytes

· mediate humoral immunity

· B lymphocytes differentiate into

· plasma cells

· memory B cells

Humoral immunity

· foreign proteins that enter body called antigens

· injested by macrophages

· marophages expose part of injested antigen plus proteins of major histocompatibility complex on surfaces

· macrophages then contact lymphocytes

· T₄ cells bind to antigen and MHC-II protein on surface of macrophage

· T₄ cells become activated and contact B cells

· B cells activated

· proliferate and transform into memory B cells and plasma cells

· plasma cells secrete antibodies into circulation

· antibodies called immunoglobulins

· large number of antigens can be recognised by lymphocytes

· ability is innate and develops without exposure to antigen

Immunoglobulins

· 5 types produced

· consist of

1. 2 light chains

· two types

· kappa and lambda

2. 2 heavy chains

· 5 types

· correspond to types below

· gamma, alpha, miu, delta and epsilon

· shaped like Y

· stem is Fc fragment

· arms are Fab fragment

Types

· IgG

· function is complement fixation

· IgA

· function is localised protection in external secretion

· IgM

· function is complement fixation

· IgD

· function is antigen recognition by B cells

· IgE

· function is reagin activity

· releases histamine from mast cells

Major histocompatibility complex

· genes of MHC located on short arm of chromosome 6

· code glycoproteins located on surfaces of all cells

· function in distinguishing self from nonself

· three major loci

Class 1-loci

· encode for of HLA-A, HLA-B and HLA-C

· found on all cells except RBCs

· primary factors in

· self-recognition

· development of tolerance

Class II-loci

· encode for HLA-DR, HLA-DQ and HLA-DP

· involved in antigen presentation to T cells

· present on macrophages, B cells and activated T cells

Class III-loci

· encode for proteins of complement cascade

Complement system

· when antigens combine with circulating antibodies

· cells lysed

· bacteria opsonised

· leukocytes attracted to antigen

· histamine released

· mediated by plasma enzymes called complement

· enzymes numbered C1 to C9

· C1 binds to immunoglobulins that have bound antigen

· triggers series of events that activates other components of system

Cellular immunity

· mediated by T₈ cells

· activated when presented with antigen and MHC-I protein

· proliferate and differentiate into

· memory T cells

· cytotoxic T cells

· suppressor T cells

· cytotoxic cells kill by

· inserting pore-forming molecules into membranes of target cells

· inserting toxins into target cells

· supressor cells help to terminate immune response

· memory cells responsible for accelerated response to second exposure