The frequency and fine specificity of B cells responsive to (4-hydroxy-3-nitrophenyl)acetyl in aged mice

Abstract The B-cell response to NP-Hy of two murine strains has been analyzed in order to evaluate the affects of aging on B-cell repertoire expression. The results indicate that for both BALB/c mice (Igh a ) and B10.D2 mice (Igh b ) the frequency of (4-hydroxy-3-nitrophenyl)acetyl (NP)-responsive splenic B cells is approximately twofold lower, on a per B cell basis, in aged mice as compared to young adults. However, as with previous assessments of the response to DNP-Hy in aged mice, the frequency of newly generated surface immunoglobulin negative bone marrow precursor cells specific for NP in aged BALB/c mice is the same as in young mice. The decrease in frequency of responsive splenic B cells is not accompanied by a measurable decrease in repertoire diversity or changes in clonotype distribution as assessed by (a) representation of κ vs λ light chain-bearing antibodies, (b) binding of monoclonal antibodies to a panel of analogues of NP, and (c) the proportionate representation of B10.D2 monoclonal antibodies that bear NP d idiotypic determinants. By these criteria it appears that down-regulation of B cells as they mature and emerge from the bone marrow of aged mice is pan-specific and does not disproportionately affect B cells of a predominant clonotype family. Consistent with other investigations which have demonstrated differences in secreted antibodies of immunized aged vs young mice, we have observed that 4 weeks after immunization of B10.D2 mice with NP-BSA, the frequency of newly generated secondary B cells is lower in aged than in young mice and the generation of λ-bearing secondary precursor cells is particularly low. Thus, clonotype-specific down-regulation may play a role in shaping the B-cell repertoire subsequent to immunization of aged mice.