Down-regulation of membrane immunoglobulin-associated proteins, MB-1, B29 and Lyn, in AIDS-lymphomas and related conditions.

B-lymphocytes infected with Epstein-Barr virus (EBV) can proliferate in immunocompromised hosts to form lymphomas (MLs). Similar MLs are produced in mice with severe combined immune deficiency (SCID) by transfusion of human lymphocytes infected with EBV (SCID-EBV-positive BML). Mb-1 and B29 are recently found transmembrane proteins associated with membrane immunoglobulins (mIg) on the surface of B cells. Lyn is a src family gene product expressed in B cells submembranously, in association with mIg, possibly through Mb-1/B29 heterodimer. These mIg-associated proteins (Mb-1, B29 and Lyn) are known to mediate antigenic stimulation through mIgs. We noted recently that Lyn is decreased selectively in around a half of SCID-EBV-positive BMLs. We extended this line of investigation to other mIg-associated proteins. Five acquired immunodeficiency syndrome (AIDS)-MLs and ten SCID-EBV-positive BMLs were first analysed by immunohistochemistry for the expression of Mb-1, B29 and Lyn. It was found that in AIDS-MLs, all the mIg-associated proteins were heavily down-regulated. In SCID-EBV-positive BMLs, Mb-1 was down regulated in six of ten, B29 in nine of ten and Lyn in six of ten, whereas no down-regulation was noted in eight EBV-free B MLs that were also maintained in SCID mice. An additional flow-cytometric study of two SCID-EBV-positive and two EBV-negative BMLs showed similar down-regulation in the former cases exclusively. Whereas mIg was also decreased in three of five SCID-EBV positive BMLs, it did not necessarily match the decrease of mIg-associated proteins, which contrasts with the recent finding that mIgs coexist with Mb-1 or B29. Some EBV-encoded proteins may activate host molecules located downwardly; this, in turn, may lead to the suppression of these upwardly-located mIg-associated proteins.