Humoral immunity due to long-lived plasma cells.

Conventional models suggest that long-term antibody responses are maintained by the continuous differentiation of memory B cells into antibody-secreting plasma cells. This is based on the notion that plasma cells are short-lived and need to be continually replenished by memory B cells. We examined the issue of plasma cell longevity by following the persistence of LCMV-specific antibody and plasma cell numbers after in vivo depletion of memory B cells and by adoptive transfer of virus-specific plasma cells into naive mice. The results show that a substantial fraction of plasma cells can survive and continue to secrete antibody for extended periods of time (>1 year) in the absence of any detectable memory B cells. This study documents the existence of long-lived plasma cells and demonstrates a new mechanism by which humoral immunity is maintained.