Question

Which among the following is correct regarding primary and secondary immune responses?

• A. Primary response: IgM (High), IgG (Low), High intensity immune response
• B. Secondary response: IgM (Low), IgG (High), Low intensity immune response
• C. Primary response: IgM (Low), IgG (High), Low intensity immune response
• D. Secondary response: IgM (Low), IgG (High), High intensity immune response

Answer 1

The correct option is D Secondary response: IgM (Low), IgG (High), High intensity immune response

Primary immune response is when antigen is recognised for the first time by a B cell. When antigen is recognised, the B cell is differentiated into plasma cells, which produce the immunoglobulins.

There are mainly five types of immunoglobulins that plasma cells produce - IgM, IgG, IgA, IgD and IgE. The first antibody to be produced as a result of primary immune response is IgM (in high concentration) followed by IgG (in low concentration) and consequently generates weak and slow response.

When the same antigen is recognised for the second time or subsequent times, although the first antibody to be produced is again IgM but this time concentration of IgM is low and followed by production of high concentration of IgG, which consequently produces a fast and strong immune response.