CROSS-BINDING ACTIVITY AND PROTECTIVE CAPACITY OF MONOCLONAL-ANTIBODIES TO LIPID-A

Six hybridoma clones (1M, 4M, 9M, 11M, 18M and 31G), secreting monoclo nal antibodies (mAbs) against lipid A were obtained after fusion betwe en cells of mouse myeloma line X63-Ag8.653 and spleen cells from BALB/ c mice immunized with acid treated Salmonella minnesota bacteria coate d with additional free lipid A. The specificity and cross-binding acti vity of the mAbs were characterized in ELISA by using synthetic lipid A analogs as well as different lipid A and lipopolysaccharides (LPS) e xtracted from R- and S-form bacteria. It was found that the antibodies recognize epitopes in which phosphate groups, especially those at the C4' position of the glucosamine backbone of lipid A, were present. Th ese epitopes were accessible also for the antibodies in purified intac t LPS. By using a set of core glycolipids with increasing completion o f the core region of the molecule and S-LPSs it was shown that the mAb s cross-reacted with a variety of R- and S-form LPS. The binding activ ity decreased with increasing length of the polysaccharide chain. The mAb did not prevent ultimate lethality of mice challenged with Klebsie lla pneumoniae B and Salmonella typhimurium C5. However a delay of mor tality rate of mice pretreated with antibodies 18M and 31G and infecte d with K. pneumoniae was seen.