PRODUCTION AND CHARACTERIZATION OF MONOCLONAL-ANTIBODIES TO SIMIAN IMMUNODEFICIENCY VIRUS ENVELOPE GLYCOPROTEINS

Twelve monoclonal antibodies (MAbs), TB1 to TB12, were produced agains t a soluble vaccinia recombinant envelope glycoprotein (gp140) from si mian immunodeficiency virus SIV mac251. These MAbs recognized SIV gp14 0 with a relatively high affinity (K-0.5 from 6.7 x 10(-8) to 4 x 10(- 9) M). All the MAbs except TB9, TB11, and TB12 cross-reacted with HIV- 2 envelope glycoproteins, but none of the 12 MAbs recognized those fro m HIV-1. Using a panel of 87 overlapping synthetic peptides containing 20 amino acid residues, with an overlap of 10 amino acids and spannin g the entire primary sequence of gp140, 3 linear epitopes were identif ied. The first mapped with a neutralizing MAb, TB12, which recognized a linear sequence around amino acids 28-31 within the N-terminal end o f the external envelope glycoprotein. The two other new nonneutralizin g MAbs recognized Linear epitopes around amino acid sequence 380-381 b y MAbs TB1, TB2, and TB3, and at the transmembrane glycoprotein amino acids 581-600 by MAb TB6. Seven of the 12 MAbs, TB4, TB5, TB7-9, TB10, and TB11, failed to bind the linear synthetic peptides in ELISA. More over, among these seven MAbs only MAbs TB4, TB5, TB9, and TB10 failed to recognize SIV envelope glycoproteins in Western blot (WE) or ELISA after reduction of disulfide bridges by dithiothreitol DTT), suggestin g that they are directed against conformational or discontinuous epito pes. It is of interest to note that MAb TB10 can block the binding of gp140 to the CD4 receptor when the MAb is previously incubated with gp 140. Consistent with this result, MAb TB10 cannot bind to gp140 that h as been previously complexed with the CD4 receptor. All these results suggest that MAb TB10 recognizes a conformational or discontinuous epi tope overlapping or close to the CD4-binding site. These properties ar e probably implicated in the neutralizing activity observed with this MAb.