Early arrest of B cell development in nude, X-linked immune-deficient mice.

Mice simultaneously expressing the nude and xid mutations have a severe deficit of both mature T and B cells. We now report studies designed to determine at which point in B cell differentiation development is arrested. Nude-xid mice have normal numbers of hematopoietic colony forming units (CFU-s) but lack two early pre-B cell markers: susceptibility to transformation by Abelson murine leukemia virus (A-MuLV) and production of cytoplasmic mu (C mu) heavy chain. Thus, there is a defect in lymphocyte development prior to or early in pre-B cell differentiation but after hematopoietic stem cell formation. The monoclonal reagents DNL 1.9, 14.8 and RA3-3A1/6.1, which react with the surface protein B220 (Ly5) on pro-B, C mu- pre-B, C mu+ pre-B, and surface Ig+ B cells, revealed the presence of positive cells in nude-xid mice. The bone marrow of nude-xid mice contains more B220+ cells than C mu+ cells. Our data suggest that the developmental block in these mice occurs at the earliest identifiable step in the B lymphocyte lineage, after the appearance of B220+ C mu- pro-B cells, but before the differentiation of C mu-bearing (pre-B) cells.