HIV-1 GP41 BINDING-PROTEINS AND ANTIBODIES TO GP41 COULD INHIBIT ENHANCEMENT OF HUMAN RAJI CELL MHC CLASS-I AND CLASS-II EXPRESSION BY GP41

Based on our findings, that HIV-1 soluble gp41 could bind to several p roteins on the human, T, B and monocyte cells independently of CD4, we examined the effect of HIV-1 soluble gp41 (sgp41; Env amino acids 539 -684) on surface expression of MHC I and II, ICAM-1 and CD21 molecules on human Raji cells. Flow cytometry (FACS) analysis demonstrated that sgp41 could selectively enhance MHC class I and II expression on Raji cells, but did not increase expression of other cell surface antigens , such as, CD21 and CD54 (ICAM-1). Soluble gp41 could also enhance MHC class I and II expression on another human B cell line, Bjab. The sgp 41-dependent enhancement of the MHC class I and II expression on Raji cells is time- and dose-dependent. The sgp41 enhancement effect on the MHC antigen expression could be inhibited by the gp41-binding protein s of 45, 49 and 62 kD (isolated from Raji-lysate) which could inhibit the sgp41-binding to Raji cells. Interestingly, this sgp41-dependent e nhancement of the MHC class I and II expression could also be inhibite d by two mAbs to HIV-1 gp41, but not by a third mAb binding to a diffe rent site on gp41. These results demonstrate that HIV-I sgp41 can sele ctively enhance the human Raji cell MHC class I and II antigen express ion and this enhancement effect could be inhibited by the sgp41-bindin g proteins and anti-gp41 antibodies, and suggest that the sgp41-depend ent enhancement is mediated by its binding to Raji membrane proteins o f 45, 49 and 62 kD.