TOPIC- PRIMARY IMMUNE RESPONSE

INTRODUCTION TO MICROBIAL WORLD.

RASHIKA SOODRUPALI CHAUHAN

Primary and secondary immune responses are like a soccer game…

The first time you play another team, you don’t know how they play…

They could be great players…

…or they could be horrible players.

So it takes you a good half of the game to understand and get settled….

But if you play again with them for the second time…You can quickly start playing hard because you remember how they played before.

•Primary response is the immune response of the body to new antigens.

•When a new pathogen enters in to the body, immune system takes little time to respond.

•During this period immune system learns about the pathogen and gets ready to eliminate it from the body.

The preparation period that is the period between entry of pathogen and expression of immune response is known as "latent period".

Latent period in humoral immunity indicates activation and proliferation of naive B cells to produce plasma cells and memory cells.Plasma cells secrete antibodies and memory cells store information of the pathogen.

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Generally IgM type antibodies with a half life of 5 days are produced in primary response.

Concentration of secreted antibodies is different at different stages of latent period:-

•In the initial, stage antibodies against the new antigens are almost absent, and this period is known as "Lag phase".

•Antibodies gradually rise from zero stage to a maximum and this raising period is referred as "Log phase".

•After attaining maximum, antibody levels remain constant for some time and the period with constant antibody levels is referred as "plateau phase".

•Plateau phase is accompanied by a decline phase, indicating reduction of Antibodies.

•Presence of antigen is necessary for the production of plasma cells. Since the antigens are removed by the action of antibodies, B cells fail to get stimulation from antigens and stops producing plasma cells.

•The number of plasma cells producing Abs gradually decreases due to their short life. Death of plasma cells producing antibodies and drop in the formation of plasma cells leads to a reduced Abs level in the decline phase. If a graph is plotted for the Abs titer against time in an immune response, it gives a typical sigmoid curve with an extended decline phase

Comparison on amount of antibody production in primary and secondary immune response.

Dynamics of Antibody Production

• Antibody production

– Initial antibody produced in IgM

– Lasts 10-12 days

– Followed by production of IgG

– Lasts 4-5 days

– Without continued antigenic challenge antibody levels drop off, although IgG may continue to be produced.

Duration of latent period in primary immune response varies from several hours to days. It depends on many factors such as type of antigen, amount of antigen entered, rout of entry, health status of the individual etc. For instance latent period is few hours for pneumococcal antigen but 2- 3 weeks for diphtheria.