PROTECTIVE EFFECT OF ANTILIPOPOLYSACCHARIDE MONOCLONAL-ANTIBODY IN EXPERIMENTAL KLEBSIELLA INFECTION

An O-antigen-specific murine monoclonal antibody (MAb) directed agains t an immunodominant epitope expressed on Klebsiella O1, O6, and O8 lip opolysaccharides (LPS) was examined with respect to its binding to non encapsulated and encapsulated bacterial cells and its ability to prote ct against lethal murine Klebsiella sepsis, While the MAb (clone Ru-O1 , mouse immunoglobulin G2b) bound well to nonencapsulated organisms of the O1 serogroup, binding,vas significantly, but not completely, abol ished by the presence of the K2 capsule. in a model of experimental Kl ebsiella peritonitis and sepsis induced by a virulent O1:K2 serogroup strain, higher doses of anti-LPS MAb Ru-O1 than of a previously descri bed anticapsular MAb specific for the K2 capsular polysaccharide were needed to provide protection, However, high-dose (40 mu g/g of body we ight) pretreatment with anti-LPS MAb Ru-O1 significantly reduced bacte rial dissemination to various organs as well as macroscopic and histol ogic pulmonary alterations. Thus, since the number of Klebsiella capsu lar antigens occurring in clinical material is too large to be complet ely ''covered'' by a K-antigen-specific hyperimmunoglobulin preparatio n, O-antigen-specific antibodies may supplement K-antigen-specific imm unoprophylaxis and -therapy of clinical Klebsiella infection.