Fish Immunology (1+1)

Unit 9- Immune response

9.2. Primary immune response
When a new pathogen enters in to the body, specific immune system is activated and mounts an immune response against that pathogen, this immune response to the new antigens is known as primary response. Primary immune response results in a proliferation of B-cells that were stimulated by pathogens. If the antigen is given as vaccine then the the first injection of the antigen producing primary immune response is called priming dose.
The period between the invasion of pathogen and expression of immune response is known as "latent period" which can vary from several hours to days. This latent period depends on the factors like type of antigen, amount of antigen entered, rout of entry, health status of the individual etc. In this latent period the immune system prepares to activate and proliferate the lymphocytes which produce plasma cells and memory cells.
Plasma cells secrete antibodies and memory cells store memory of the pathogen. During primary response IgM type of antibodies are produced with a half life of 5 days. Secreted antibodies are different at different stages of latent period.
The amount of antibodies produced by the immune response to antigen is called antibody titre. The antibody titre plotted against time gives a sigmoid curve called immune response curve. The curve obtained for primary immune response is
called primary immune response curve.
In the initial phase of infection non specific immune response activates followed by specific immune response and that’s the reason in initial stage antibodies against the antigens are almost absent, and this period is known as “Lag phase”. Later the concentration of antibodies rises and this raising period is referred as “Log phase”. Once the antibody level attains maximum it remains constant for some period called as “plateau phase”. If the level of antibody remains constant for several days indicates that the antibodies are produced and replaced the antibodies that were lost. After plateau phase the level of antibodies starts to decrease called decline phase.
The antigen is necessary to stimulate immune response which intern produce antibodies from plasma cells. After the removal of antigens by the antibodies, B-cells are not stimulated which intern stops producing plasma cells. Some of the B-cells are stored as memory cells.