Immune response Pathophysiology

Immune response Body’s response to antigens It is the third line of defense Antigens include – viruses, bacteria, fungi, parasites, pollens, food, venom, drugs, vaccines, transfusion. Transplanted tissues IR is Mediated by immunoglobulins and lymphocytes B lymphocytes – multiply and produce Ig [clonal selection T lymphocytes – directly attack Ag in cell-mediated immunity [CMI] Responsible for acquired [after birth] immunity

Lymphoid organs – sites of B ,T cell differentiation

Induction of IR Antigens – have a part [antigenic dterminant/ epitope] which can be bound by a paratope/Ag binding site. Immunogenicity depends on size, foreignness, complexity & amount. The body is tolerant to self Ag. Haptens are too small on their own but become immunogenic when combined with larger molecules Blood group antigens – Antigen A, antigen B, Antigen A and B. blood group O has neither of the antigens Rhesus positive [DD or Dd genotype]. Rh negative [dd] do not express the Ag

Humoral immunity After generation of clonal diversity become B lymphocytes B cells are activated by Ag to multiply [clonal selection] into: Plasma cells which secrete Ig Memory cells responsible for subsequent response to Ag

Immunoglobulins Five types – IgA, IgD, IgE, IgG, IgM [alpha, delta, Epsilon, gamma, Mu]– with antigenic, structural and functional differences

Functions of Ig Neutralizing bacterial toxins – form Ag-Ig complexes which precipitate out of body fluids/solutions and get phagocytosed Neutralizing viruses – and prevent viral entry into cells. Essence of vaccination Opsonizing bacteria – opsonise and induce opsonization by complement system Activation of inflammation – while the Fab binds to Ag, Fc amplify the inflammatory response

Secretory immune system Ig produced in body fluids other than blood: tears, sweat, saliva, mucus, breast milk to protect external body surfaces. Produced by B cells in the organs

Primary and secondary response

Cell mediated immunity Mediated by T cells which mature in the thymus Lymphokine producing cells - transfer delayed hypersensitivity, activate other cells [macrophages] Cytotoxic cells (Tc) – attach Ag, destroy cells with foreign Ag T helper cells – Th – control CMI and humoral immunity Suppressor T cells – Ts – control CHI and HI Natural killer cells – kill Ag infected and tumor cells

Effects of CMI Cytotoxicity – direct cellular killing of virally infected cells, tumors or foreign grafts. APC express Ag on their MHC [Histocompatibility antigen complex] Delayed hypersensitivity – influence of other cells Memory – responsible for a faster response against subsequent antigenic challenges Control – of HI and CMI