B lymphocyte lineage cells in newborn and very young NZB mice: Evidence for regulatory disorders affecting B cell formation

As adults, NZB mice have a severe deficiency of identifiable precursors of B lymphocytes, but this is preceded by a time when B cells and their immediate precursors are present in bone marrow in elevated numbers. Our present studies indicate that the final stages of B cell formation may be proceeding at a greater than normal rate at 4 wk of age. At this time, large numbers of slg^- B cell precursors can be identified in NZB but not in CBA/H or DBA/2 marrow that can respond to mitogens in semisolid agar cultures without preculture. Colony formation by these precursors was dependent on the presence of Sephadex G-10-adherent cells in the suspensions. In this respect, 4-wk-old NZB marrow was similar to spleen and liver of normal CBA/H newborn mice. Mixing experiments suggested that hyperactive regulatory cells present in young NZB marrow may promote functional maturation of normal pre-B cells from CBA/H or DBA/2 mice. In addition, potent substances present in the serum of young but not older NZB mice produced the same effect. Factor-mediated enhancement of clonal proliferation by slg^- precursors was not dependent on adherent cells and required more than brief exposure of the cells to young NZB serum. These are all indications that abnormalities of B lineage differentiation in young NZB marrow may be attributable to microenvironmental elements. Congeneic, B cell-deficient NZB.xid mice, however, lacked hyperactive regulatory cell function and serum factors that characterize NZB mice of this age. A study was also made of B cell precursors in newborn spleen and liver of NZB mice, and abnormal shifts of populations of B lineage cells were already present by that time. These observations support previous contentions that humoral immunity is precocious and abnormally regulated in NZB mice.