Characterization of a proteolytic-enzyme inhibitor with allergenic activity. Multiple functions of a parasite-derived protein

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Abstract
A trypsin inhibitor from the tick Boophilus microplus was purified by ion-exchange chromatography and gel filtration. The protein undergoes reversible polymerization, dissociating at low pH. The apparent MW measured by electrophoresis on polyacrylamide gels containing sodium dodecyl sulphate is 18,500. Inhibition of trypsin occurs by formation of a 1:1 molar complex. Chymotrypsin is inhibited, though the dissociation constant of the complex formed is larger than with trypsin. The protein possesses independent sites for the inhibition of chymotrypsin and trypsin. The inhibitor preparation gives an immediate hypersensitivity reaction on intradermal injection into cattle that were exposed to the tick. The allergenic activity is due to the inhibitor protein itself and not to contaminating material, since the 2 activities were not separated during purification or in 2 subsequent affinity-chromatography procedures. The hypersensitivity reaction is a true immunological response, since it is found in almost all cattle that were exposed to the tick, but not in unexposed animals. Passive cutaneous anaphylaxis can be demonstrated with serum from exposed, but not from unexposed, animals.