RTX TOXINS RECOGNIZE A BETA-2 INTEGRIN ON THE SURFACE OF HUMAN TARGET-CELLS

Actinobacillus actinomycetemcomitans leukotoxin and Escherichia coli a lpha-hemolysin are RTX toxins that kill human immune cells. We have ob tained a monoclonal antibody (295) to a cell surface molecule present on toxin-sensitive HL60 cells that can inhibit cytolysis by both RTX t oxins. Utilization of this monoclonal antibody for immunoaffinity puri fication of detergent-solubilized target cell membranes yielded two po lypeptide chains of approximate molecular masses of 100 and 170 kDa. M icrosequencing of tryptic peptides from the two proteins showed comple te homology with CD11a and CD18, the two subunits of the beta 2 integr in, lymphocyte function-associated antigen 1 (LFA-1). Anti-CD11a and C D18 monoclonal antibodies also inhibited RTX toxin-mediated cytolysis. Direct binding experiments demonstrated the ability of an immobilized RTX to bind LFA-1 heterodimers present in a deter gent lysate of huma n HL60 target cells. Transfection of CD11a and CD18 integrin genes int o a cell line (K562) that is not sensitive to either RTX toxin resulte d in LFA-1 expressing cells, KL/4, that were sensitive to both toxins. These experiments identify LFA-1 as a cell surface recep- tor that me diates toxicity of members of this family of pore-forming toxins.