Abstract
The human foamy virus is a complex retrovirus that codes for several regulatory 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 comparable 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 Vp‐specific manner. The recombinant Bel 3 protein purified to near homogeneity was assayed in vitro to determine whether or not it functions as a superantigen that stimulates human T lymphocytes expressing particular Vβ T cell receptor (TCP) chains. Therefore, an analysis including all known human Vβ elements was performed. The expression of different Vβ chains of the TCR was analyzed by reverse transcription of the Vp RNAs and subsequent amplification of the corresponding Vβ cDNA elements by polymerase chain reaction in unstimulated, phytohemaggluttinin (PHA)‐ and Bel 3‐stimulated human T lymphocytes. In addition, eight monoclonal antibodies directed against particular Vβ family members were used to determine any change in the expression of the remaining known Vβ elements upon treatment with PHA and Bel 3. The comparative Vp‐specific transcriptional analysis revealed that the in vitro expression of the Vβ18 chain was specifically and strongly expanded in Bel 3‐stimulated human T cells, a property characteristic for a superantigen. © 1994 Wiley‐Liss, Inc.