Questions: Identify characteristics of a secondary immune response: Select all that apply - It occurs after the second and subsequent exposures to an antigen. - Antibodies first appear within hours, peaking at day 3. - IgG antibodies are formed first.

The characteristics of a secondary immune response include:

1. It occurs after the second and subsequent exposures to an antigen.

   • This is correct. A secondary immune response is triggered when the immune system encounters an antigen that it has previously been exposed to. The immune system has memory cells that recognize the antigen and respond more rapidly and effectively.

2. Antibodies first appear within hours, peaking at day 3.

   • This is correct. In a secondary immune response, memory B cells quickly recognize the antigen and produce antibodies within hours, with levels peaking around day 3.

3. It occurs with the first exposure to an antigen.

   • This is incorrect. The first exposure to an antigen triggers a primary immune response, not a secondary one. The secondary response occurs upon subsequent exposures.

4. Antibodies first appear 3-6 days after exposure, peaking at day 10.

   • This is incorrect. This description is characteristic of a primary immune response, where the immune system takes longer to produce antibodies.

5. IgM antibodies are formed first.

   • This is incorrect for a secondary immune response. IgM antibodies are typically the first to be produced in a primary immune response.

6. IgG antibodies are formed first.

   • This is correct. In a secondary immune response, IgG antibodies are produced more rapidly and in greater quantities than in a primary response.

In summary, the characteristics of a secondary immune response are that it occurs after the second and subsequent exposures to an antigen, antibodies first appear within hours peaking at day 3, and IgG antibodies are formed first.