Virus-Induced Maturation and Activation of Autoreactive Memory B Cells

We have examined B cell populations that participate in distinct phases of the immune response to the influenza virus A/PR/8/34 hemagglutinin (HA) for their susceptibility to negative selection in mice that express the HA as a neo–self-antigen (HA104 mice). We demonstrated previously that specificity for the neo–self-HA causes a population of immunoglobulin G antibody-secreting cells, which dominate the primary response to virus immunization in BALB/c mice, to be negatively selected in HA104 mice. We find here that in contrast to these primary response B cells, HA-specific memory response B cells developed equivalently in HA104 and nontransgenic (BALB/c) mice. Indeed, there was no indication that HA-specific B cells were negatively selected during memory formation in influenza virus–immunized HA104 mice, even though the neo–self-HA can be recognized by memory B cells. Furthermore, HA-specific autoantibodies were induced in the absence of virus immunization by mating HA104 mice with mice transgenic for a CD4⁺ HA-specific T cell receptor. These findings indicate that specificity for a self-antigen does not prevent the maturation of autoreactive B cells in the germinal center pathway. Rather, the availability of CD4⁺ T cell help may play a crucial role in regulating autoantibody responses to the HA in HA104 mice.