CATHEPSIN L PROTEINASE SECRETED BY FASCIOLA-HEPATICA IN-VITRO PREVENTS ANTIBODY-MEDIATED EOSINOPHIL ATTACHMENT TO NEWLY EXCYSTED JUVENILES

Cathepsin L-like activity was demonstrated in the excretory/secretory (E/S) products of Fasciola hepatica newly excysted juveniles (NEJ), 3- week-old, 5-week-old and mature flukes using the fluorogenic substitut ed 7-amino-4-methylcoumarin substrates Z-phe-arg-AMC, Z-arg-arg-AMC an d Z-arg-AMC. Gelatin-substrate polyacrylamide gel analysis revealed th at the E/S from each of these stages contained multiple proteolytic en zymes; however, the pattern of proteinases obtained for NEJ E/S differ ed markedly from that of all other stages examined. The four NEJ prote inases identified were inhibited by leupeptin and z-phe-ala-diazomethy l ketone indicating that each had cathepsin L-like activity. The E/S p roducts of all four developmental stages contain an enzyme capable of cleaving immunoglobulin at the hinge region, the activity of which is also inhibited by z-phe-ala-diazomethyl ketone. Using in vitro cell at tachment assays we show that the cathepsin L-like proteinase purified from the E/S products of adult F. hepatica can prevent the antibody-me diated attachment of eosinophil to NEJ. These experiments indicate tha t this proteinase has an important biological function in immune evasi on.