Secondary immune response is mediated by ?

Ans. is 'a' i.e., IgG Immune response The antibody response to an initial antigenic stimulus differes qualitatively and quantitatively from the response to subsequent stimuli with same antigen. Former is called primary response and the latter secondary response. a. Primary response Primary imnme response refers to the first encounter of immune system with an antigen. The antibody that is elicted first is entirely of the IgM type. IgM antibody titre rises to a peak level and then declines almost as fast as it developed. In a few days IgG appears. IgG titre rises gradually and then declines gradually. An impoant outcome of primary antigenic challenge is the production of memory cells( primed cells). b. Secondary response A secondary response refers to a re-encounter of the same antigen against which memory cells ( T and B cells) have developed during primary exposure. As primed cells are already present antibody response is very fast with no lag phase as compared to primary response which has slow response with lag phase ( as there are no primed cells in primary response) There is brief production of IgM, but the major antibody is IgG4 which is prodced in larger amount and for longer duration.