PROTEINASES SECRETED BY FASCIOLA-HEPATICA - TIME-COURSE OF THE INHIBITORY EFFECT OF SERUM FROM EXPERIMENTALLY INFECTED-RABBITS DEMONSTRATEDBY GELATIN-SUBSTRATE POLYACRYLAMIDE-GEL ELECTROPHORESIS

Fasciola hepatica secretes proteolytic enzymes to aid it to penetrate and migrate through the host tissues. Two of these proteinases have be en purified and shown to be cathepsin L-like, and are termed, CL1 (27. 5kD) and CL2 (29kD). The immunogenicity of these proteinases was inves tigated over the course of an experimental infection and following dru g treatment. Four groups of rabbits were studied: group 1: orally infe cted with 50 metacercariae; group 2: infected and treated 8 weeks afte r infection; group 3: infected, treated at week 8 and reinfected at we ek 13 and group 4: non-infected control group. Sera were collected wee kly from each group until week 20 postinfection. CL1 and CL2 were incu bated with the different sera and then analysed by gelatin substrate p olyacrylamide gel electrophoresis (GS-PAGE). Analysis of groups 1, 2 a nd 3 showed that CL1 and CL2 neutralizing antibodies appear at week 5 postinfection. In group 1, these remained throughout the 20 weeks of i nfection. In group 2, neutralizing antibodies disappeared at week 13, that is, 5 weeks after anti-Fasciola treatment. In group 3, CL1 and CL 2 neutralizing antibodies disappeared at week 13 but reappeared by wee k 15, that is 2 weeks after reinfection. Pooled sera from group 4, sho wed no inhibitory capacity. ELISA results using CL1 and CL2 as antigen , correlate very well with the inhibitiory time course observed by GS- PAGE. These results suggest that purified cathepsin Ls are antigenic m olecules recognized early in the infective process and capable of indu cing a specific humoral response, strong enough to neutralize, at leas t partially, their enzymatic activity.