Immunological Memory in Humans Has Been Examined by Assessing Responses

Multiple Choice

Immunological memory in humans has been examined by assessing responses in individuals who were given the vaccinia virus to induce immunity against smallpox. Antiviral CD4 and CD8 T cell responses could be detected many years after the vaccinia immunization, but declined with an estimated half-time of about 10 years. In contrast, antiviral antibody responses were maintained at a relatively constant level, with a barely detectable decline over decades. The persistence of antiviral antibodies for years after immunization is likely due to:

A) The presence of CD4 T cell help for memory B cells
B) The presence of long-lived antibody secreting plasma cells
C) The periodic reactivation of memory B cells by low levels of antigen exposure
D) The persistence of the virus in the immunized host
E) The presence of pro-survival cytokines, such as IL-7 and IL-15