THE HUMAN MONOCYTE CELL-LINE U937 BINDS HIV-1 GP41 BY PROTEINS OF 37,45, 49, 62 AND 92-KDA

Based on our findings that HIV-1 gp41 independently of CD4 can bind to the helper T cell line H9 and B cell line Raji, we characterized the putative binding of HIV-1 gp41 to the monocyte cell lines U937 and HL6 0. Using flow cytometry (FACS) we examined the binding of soluble gp41 (sgp41; env amino acids 539-684) to these monocyte cell lines. Using sgp41 attached to Sepharose beads, U937 cell lysates were absorbed. Th e sgp41 eluate of U937 cell lysates could inhibit sgp41 binding to U93 7 cells. With SDS-PAGE of sgp41 eluate of U937 cell lysates, three str ong protein bands (37, 45 and 62 kDa) and two weak bands (49 and 92 kD a) were stained with Coomassie blue. With Western blot (ligand blot) a nalysis using sgp41, three strong protein bands (37, 49 and 62 kDa) an d a very weak band (42-45 kDa) were observed in sgp41 eluate of U937 c ell lysates. The results suggest that the four proteins 37, 42-45, 49 and 62 kDa in U937 cell lysates are possible candidates for the putati ve gp41 receptor(s). We compared the blocking activities of sgp41 elua tes from different cell lysates. Not only U937 and Raji lysate-sgp41 e luates, but also H9 and HL60 lysate-sgp41 eluates could block sgp41 bi nding to U937 and Raji cells. The results indicate that the sgp41-bind ing proteins on U937, or Raji (H9 and HL60, respectively) probably cou ld have an identical blocking (or binding) specificity; these cell typ es carry very similar receptor(s) for HIV-1 gp41 binding.