Question

Why does a person who has had chicken-pox before, becomes immune to subsequent attacks of the same disease?

Answer 1

When a person suffers from chickenpox for the first time, the pathogen (varicella virus) acts as an antigen and triggers the primary immune response. This produces:

(i) Effector cells — B and T cells which destroy the virus and cure the disease.

(ii) Memory cells — a large clone of B- and T-memory cells specific to the varicella virus.

These memory cells remain in the lymph nodes for a very long time, often for life. When the same virus attacks the body again, these pre-existing memory cells recognise the antigen immediately and initiate a rapid and strong secondary (anamnestic) immune response. A large number of antibodies and cytotoxic T cells are produced so quickly that the pathogen is destroyed before it can cause the disease.

Because the memory cells give a rapid and heightened secondary response, a person who has already had chickenpox becomes immune to subsequent attacks of the same disease.