A role for mature B cells in bone marrow transplantation

The proliferative potential of membrane Ig (mIg)-bearing B lymphocytes was assessed in an adoptive transfer system based on the use of non-inbred rabbits matched for major histocompatibility (MHC) antigens and mismatched for immunoglobulin (Ig) allotypes. Cell suspensions made from spleens (SP), mesenteric lymph nodes (LN), or bone marrow (BM) of allotype b4b5 rabbits were deprived of B cells with mIg of the b4 type by adherence to plastic dishes coated with affinity-purified anti-b4. When such b4-depleted cell populations were injected into newborn hosts of allotype b6b6, stable and lasting chimerism promptly resulted, in which donor-derived products were almost entirely of the b5 allotype. Chimeras formed by transfer of unfractionated cells from b4b5 donors, on the other hand, exhibited a predominance of the b4 allotype, as seen in the living donors. BM but not SP or LN contained precursors capable of differentiating into mIg+ lymphocytes in culture, but no evidence was obtained for engraftment and differentiation by such B-cell precursors or more primitive stem cells in vivo. These studies suggest a potentially significant role for mature B cells in reconstituting the immune system of human transplant recipients.