Humoral Immunity Against Viral Infection

Induction of specific immune response

·         Viruses don’t stimulate B and T cells directly but presented to the immune system by macrophages.

·         Primary immune response takes 10 days, while secondary immune response takes 2-3 days (depends on memory induced by the primary response).

·         Viral infection is limited by antibodies from B cells and cytotoxic T cells (Tc).

·         B and T cell precursor require interaction with T helper cells (CD4) to maturate into functional cells(CD8).

·         Activated T helper cells produce lymphokines which accelerate clonal expansion of primed B and T cells.

T-helper cells

·         Arises from stem cells in bone marrow and migrate to thymus to maturate.

·         Maturation by rearrangment genes encoding TCR. Once maturate, it migrate to blood and lymphatic system.

·         If they bind with antigen presented by MHC II of antigen presenting cells like macrophages and if those cells send the proper signals, T-help become activated and divide.

·         Some progeny become effecter cells, live shortly and produce lymphokines have controlling effect on other immune cells.

·         Other progeny become memory cells and stay in body for years to become activated with subsequent exposure to antigen.

·         T-h cells carry a protein on their surface known as CD4 which help recognition of MHC class II.

a)    Humoral immunity (Antibody response):

          B cells produce immunoglobulins:

• IgM: Pentameric -  remains in the plasma.
• IgG: Enters tissue spaces during inflammation

o   Transported across placents (rodents), Yolk

o   sac (eggs) and through colostrum(ruminants).

• IgA: Responsible for mucosal immunity (local

           immunity) Seceretory antibody – Produced by

           cells of mucosal surfaces – trypsin resistant.

   The three classes are presented in the colostrum of domestic animals.