EXTRACELLULAR-MATRIX DEGRADATION BY HAEMONCHUS-CONTORTUS

To better understand the in vivo function of secreted cysteine proteas es of Haemonchus contortus, the ability of live parasites to degrade c onnective tissue was investigated using [H-3]proline-labeled extracell ular matrix produced by smooth-muscle cells (R22). The matrix was comp osed of glycoprotein(s) (34%), elastin (49%), and collagen (15%) in an insoluble, multilayered, cross-linked structure. No degradation of th e extracellular matrix by third-stage larvae (L3) (10,000/ml) occurred during 24-hr in vitro incubation. In contrast, fourth-stage larvae (L 4) (1,000/ml) degraded 42% of the matrix, whereas adults (100/ml) degr aded the entire matrix. The presence of Z-phe-ala-FMK (100 mu M), a sp ecific cysteine protease inhibitor, during incubation of adults, reduc ed matrix degradation to 30% without affecting parasite motility. Isol ated adult excretory/secretory products (ESP) (0.1 mg protein/ml) degr aded 64% of the total matrix; specific degradation consisted of 80.3% of the glycoprotein, 67.1% of the elastin, and 27.6% of the collagen m atrix components. Degradation of the matrix by ESP was stimulated by d ithiothreitol (2 mM) and inhibited by Z-phe-ala-FMK. Thus, the secreto ry cysteine proteases of H. contortus are active under physiological c onditions and able to degrade the major components of connective tissu e in an in vitro model system that simulates their structure in vivo. These data strengthen the proposed role of these enzymes in the breakd own of host tissue.