B cell memory in xid mice is long-lived despite reduced memory B cell frequency.

Brutons tyrosine kinase (Btk) deficient xid mice have a diminished primary T cell dependent immune response, resulting in a reduced memory B cell frequency. Boosting at 35 days post primary immunization, however, generates a normal secondary immune response, indicating a functional memory B cell compartment. The longevity of B cell memory appears to depend on both the presence of antigen and expression of cell survival genes such as bcl-2. Since there is a natural decay in the number of memory B cells over time and since xid B cells have been demonstrated to have reduced Bcl-2 levels, we aimed at determining whether B cell memory of xid mice would be long-lasting. This report demonstrates that memory B cell precursors are detectable in xid mice more than 100 days after primary immunization. Furthermore, a secondary immune response of normal magnitude and kinetics can be generated in xid mice at 150 days after primary immunization indicating that B cell memory is long-lived in xid mice. Thus, although survival of B cell memory is presumably dependent on immunoglobulin (Ig)-mediated interaction with antigen, this interaction does not depend solely on signalling through Btk.