Question

Compare and contrast the immune system’s primary response to an antigen and secondary response to that same antigen.

Answer 1

In a primary immune response, naive B cells are stimulated by antigen, become activated, and differentiate into antibody-secreting cells that produce antibodies specific for the eliciting antigen. A secondary immune response is elicited when the same antigen stimulates memory B cells, leading to the production of greater quantities of specific antibodies that are produced in the primary response.

Some of the differences between Primary and Secondary Immune Response are as follows:

Characteristics	Primary Immune Response	Secondary Immune Response
Definition	Primary Immune Response is the reaction of the immune system when it contacts an antigen for the first time.	Secondary Immune Response is the reaction of the immune system when it contacts an antigen for the second and subsequent times.
Appearance	Appears mainly in the lymph nodes and spleen.	Appears mainly in the bone marrow and then, in the spleen and lymph nodes.
Responding Cell	Naive B cells and T cells	Memory B cells
Antibodies	Both thymus-dependent and thymus-independent antibodies are involved in the primary immune response.	Only thymus-dependent antibodies are involved in the secondary immune response.
Types of Antibodies	A large amount of IgM and a small amount of IgG are produced during the primary immune response.	A large amount of IgG, a small amount of IgM, IgA, and IgE are produced during the secondary immune response.