Binding of monoclonal antibody specific for domain Ia/II of Pseudomonas aeruginosa exotoxin A at pH 4 strongly neutralizes exotoxin A-induced cytotoxicity in cell culture and in vivo.
Mouse monoclonal antibodies (MAbs) against Pseudomonas aeruginosa exotoxin A (Ex-A) were established, and 4 of 20 MAbs were extensively studied for analysis of the structure-function relationship of Ex-A. IN vivo experiments demonstrated that MAb Ex-3C7 protected mice either injected with Ex-A or infected with Ex-A-producing P. aeruginosa from death caused by Ex-A at the highest rate, followed by MAbs Ex-4F2 and Ex-8H5, in that order. MAb Ex-2A10 failed to rescue the mice. MAb Ex-3C7 (immunoglobulin G1 [IgG1]) inhibited incorporation of Ex-A into target cells and strongly neutralized cytotoxicity in cell culture but did not inhibit an enzymatic activity of Ex-A, ADP-ribosyltransferase, at all. The MAb also bound Ex-A, even at a low pH of 4, and recognized amino acid residues 241 to 297 (domain Ia/II), suggesting that MAb Ex-3C7 can interfere with the conformational change and/or processing of Ex-A by keeping a complex of Ex-A and antibody stable at low pH in the phagolysosome. MAb Ex-4F2 (IgG1), which recognizes residues 550 to 590 (domain III), strongly inhibited Ex-A incorporation and neutralized cytotoxicity in cell culture but only weakly inhibited ADP-ribosyltransferase. MAb Ex-8H5 (IgG1), which recognizes residues 591 to 613 (domain III), also inhibited cytotoxicity in cell culture, but weakly. In contrast to the above three MAbs, MAb Ex-2A10 (IgG2b) greatly inhibited ADP-ribosyltransferase but showed no inhibition of Ex-A incorporation and no neutralizing activity against cell toxicity. A line of evidence indicates that (i) domain Ia/II plays an important role in the pathogenesis of Ex-A and (ii) MAbs that inhibit an intracellular postbinding process, such as conformational change, processing, and translocation of Ex-A in target cells, can display potent inhibitory activity against cytotoxicity in vivo, as well as in cell culture, and would be a good candidate for therapy of pseudomonal infections.
Biotechnology Laboratory, Takarazuka Research Center, Sumitomo Chemical Co., Ltd., Hyogo, Japan.
H
H
Ohtsuka
K
K
Horigome
A
A
Higuchi
N
N
Nomura
H
H
Ochi
S
S
Yokota
T
T
Kohzuki
H
H
Noguchi
D036002:ADP Ribose Transferases; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D001427:Bacterial Toxins; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000032:analysis; D005098:Exotoxins / Q000276:immunology* / Q000378:metabolism / Q000633:toxicity; D006863:Hydrogen-Ion Concentration; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011550:Pseudomonas aeruginosa / Q000276:immunology*; D011863:Radioimmunoassay; D013329:Structure-Activity Relationship; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D000911:Antibodies, Monoclonal; D001427:Bacterial Toxins; D000939:Epitopes; D005098:Exotoxins; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A