By means of a series of crosses and backcrosses, ZB.CBA/N mice were prepared bearing largely NZB autosomal genes, but having X chromosomes derived only from CBA/N mice. The CBA/N X chromosome carries a gene, xid, that is associated with the lack of a B cell subset necessary for most of the spontaneous autoantibody production by NZB mice. These ZB.CBA/N mice failed to develop autoantibodies to T cells, erythrocytes, or DNA. The availability of mice that were mostly NZB, but which failed to make autoantibodies, especially anti-T cell antibodies, allowed us to study possible T cell regulatory defects in NZB mice in the absence of either antibodies reactive with such T cells or other autoantibodies. We found that such mice had derangements of T cell regulation as did the NZB mice. These observations strongly suggest that the t cell abnormalities of NZB mice are not caused by the B cell hyperactivity of these mice, but rather represent independent defects. Thus, NZB mice appear to have primary defects in both the B cell population and the T cell population. Whether or not these are separate, or derive from a common precursor cell abnormality, remains to be determined.

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