Proteinases released in vitro by the parasitic stages of the bovine abomasal nematode Ostertagia ostertagi

Host tissue penetration, feeding and immune evasion by helminth parasites m ay be mediated by both mechanical processes and histolytic products release d by the parasite. The aim of this study was to investigate potential histo lytic products released during in vitro maintenance of exsheathed third (L3 ) and 4th larval stage (L4) and adult Ostertagia ostertagi. Therefore, the pH optima, substrate specificity, molecular size and inhibitor sensitivity of in vitro released (IVR) proteinases were analysed by spectrophotometry a nd substrate gel electrophoresis. It was shown that L3, L4 and adult IVR pr oteinases degrade a variety of protein substrates in a pH-dependent and sta ge-specific manner. At alkaline pH, gelatin, casein and fibrinogen were deg raded by metallo- and serine proteinases. In contrast, mucin, fibrinogen, a lbumin and haemoglobin were degraded at acidic pH by aspartyl protease- and cathepsin L-like activity. At pH 3, the heavy chain of bovine IgG was comp letely degraded by an aspartyl proteinase secreted by all 3 parasitic stage s. The specificity of the L3, L4 and adult Ostertagia ostertagi proteinases against the different substrates indicates variable functional requirement s.