EVIDENCE FOR SUPERANTIGEN ACTIVITY OF THE BEL-3 PROTEIN OF THE HUMAN FOAMY VIRUS

The human foamy virus is a complex retrovirus that codes for several r egulatory bel genes in addition to the conventional gag, pol, and env genes. The bel 3 gene is located in the 3'part of the viral genome com parable to that of the superantigen of the mouse mammary tumor virus. Superantigens bound to major histocompatibility complex (MHC) class II molecules have been shown to stimulate T cells in a V beta-specific m anner. The recombinant Bel 3 protein purified to near homogeneity was assayed in vitro to determine whether or not it functions as a superan tigen that stimulates human T lymphocytes expressing particular V beta T cell receptor (TCR) chains. Therefore, an analysis including all kn own human V beta elements was performed. The expression of different V beta chains of the TCR was analyzed by reverse transcription of the V beta RNAs a nd subsequent amplification of th e corresponding V beta cDNA elements by polymerase chain reaction in unstimulated, phytohemag gluttinin (PHA)- and Bel 3-stimulated human T lymphocytes. In addition , eight monoclonal antibodies directed against particular V beta famil y members were used to determine any change in the expression of the r emaining known V beta elements upon treatment with PHA and Bel 3. The comparative V beta-specific transcriptional analysis revealed that the in vitro expression of the V beta 18 chain was specifically and stron gly expanded in Bel 3-stimulated human T cells, a property characteris tic for a superantigen. (C) 1994 Wiley-Liss, Inc.