Physiology of murine B lymphocytes II. Life-spans of mitogen and thymus-independent antigen (type 2) reactive B lymphocytes from aged mice

We showed earlier that life spans of murine B lymphocytes could be estimated by measuring the functional reactivities of normal B cells upon transfer into x-linked immunodeficient (xid) mice, which do not respond to anti-mouse IgM (anti-μ) antibodies and thymic-independent type -2 (TI-2) antigens. Here the same approach was adopted, to evaluate the life spans of B-lymphocytes from aged mice. Spleen cells from normal young and aged mice were transferred into young or aged xid recipients and the decay kinetics were followed by measuring the proliferative response to anti-μ and PFC response to TNP-Ficoll, a prototype TI-2 antigen. The results indicated that anti-μ reactive B cells of both young and aged mice decayed with similar non-linear kinetics. About 50% of the donor cells decayed in 8-10 days, whereas, the remaining decayed at a slower rate and it appeared that the median life-expectancy of this latter population could be at least 3 weeks. Essentially, there was no apparent difference in the decay kinetics of anti-μ reactive B cells of young and aged mice. Unlike anti-μ reactive cells, TNP-Ficoll reactive B cells showed 2-3-fold enhancement in the PFC response during the first 2 weeks, and persisted at least until 5 weeks post transfer. This result indicated that TNP-Ficoll reactive B cells are long-lived. Further, it was found that the turn over rate of TNP-Ficoll reactive B.