CLEAVAGE OF IMMUNOGLOBULIN-G BY EXCRETORY-SECRETORY CATHEPSIN S-LIKE PROTEASE OF SPIROMETRA-MANSONI PLEROCERCOID

When immunoglobulin G (IgG) was incubated with Spirometra mansoni pler ocercoid (sparganum), it was cleaved into Fab and Fc fragments. Fab/c fragments were also hydrolysed. The digestion was accelerated by dithi othreitol (DTT), indicating that cleavage of IgG heavy chain was due t o a cysteine protease secreted into the medium. The responsible enzyme , of M(r)27 (+/-0.8) kDa, was purified by a series of thiopropyl affin ity, Sephacryl S-300 HR and DEAE-anion exchange chromatographies, eith er from worm extracts or from excretory-secretory products (ESP). The purified, thiol-dependent protease showed an optimal activity at pH 5. 7 with 0.1 M sodium acetate but was active over the pH range 4.5-8.0. Its activity was inhibited completely by 10(-5) M L-trans-epoxysucciny lleucylamido(4-guanidino) butane (E-64) and 1 mM iodoacetamide (IBA), but by only 53% using the specific cathepsin L inhibitor, Z-Phe-Phe-CH N2, (5 x 10(-5) M). Partial NH2-terminal amino acid sequence was sp-Se r-Val-Asn-Trp-Arg-Glu-Gly-Ala-Val-Thr-Ala-Val which showed 80%, homolo gy to human cathepsin S. Immunoblot analysis showed that sera from inf ected patients exhibited IgE antibody reaction. It is proposed that cl eavage of immunoglobulin by an excreted-secreted, cathepsin S-like, al lergenic protease is a mechanism of immune evasion used by the spargan um.