Cross-reactions among carbonic anhydrases I, II, and III studied by binding tests and with monoclonal antibodies

Cross-reactions among carbonic anhydrases (CAs) I, II, and III were studied using a variety of antisera: (1) a rabbit antiserum to bovine CA III, (2) mouse antisera to human CA I, CA II, and CA III; and (3) five monoclonal antibodies prepared by the hybridoma technique using splenocytes from a mouse immunized with human CAs I and II and bovine CA III. Cross-reactions between CAs were readily found by binding assays using these antisera. Human CA I, but not human CA II, inhibited the reaction of the rabbit anti-CA III with its homologous antigen. Mouse antisera to CA I or CA III bound the homologous I or II with nearly as great efficiency as the autologous isozyme and sometimes weakly bound CA III. Mouse antisera to CA III frequently bound CA I or II. These cross-reactions were confirmed by the first use of hybridoma-prepared, monoclonal antibodies to CAs. The mouse monoclonal antibodies to CA isozymes varied in the amount of cross-reactivity among I, III, and III: at one extreme, one monoclonal was highly specific for the autologous CA III; at the other extreme, one monoclonal weakly reacted with some examples of CSs I, II, and III.