A quantitative study on the activation of the alternative pathway of complement by mouldy hay dust and thermophilic actinomycetes

Abstract

Materials associated with the induction of farmer''s lung were incubated with fresh normal human serum in the presence of Mg ethylene glycol tetra-acetic acid (MgEGTA) or ethylene diamine tetra-acetic acid (EDTA) and results compared with zymosan activation of the alternative pathway of complement. Micropolyspora faeni organisms are as active as zymosan in reducing complement (C) levels in the presence of MgEGTA, with a 50% reduction in CH50 [total hemolytic C] at approximately 140 .mu.g/ml. Thermoactinomyces vulgaris organisms produced a 50% CH50 reduction at approximately 1.25 mg/ml, and 2 samples of respirable moldy hay dust (MHD) at approximately 5.6 mg/ml; extracts of M. faeni and T. vulgaris reduced the CH50 titer by 17% and 39%, respectively, at 16 mg/ml in the presence of MgEGTA. Organisms and extracts did not reduce the CH50 titer in the presence of EDTA even at the maximum concentration quoted by more than 3%. Alternative pathway activation was apparently responsible for C utilization in the presence of MgEGTA. Respirable MHD used less than 4% available C at 4 mg/ml in the presence of EDTA, but at 8 mg/ml dust, 11% and 28% available CH50 were used compared with 79% and 81% respectively in the presence of MgEGTA. The elution of immunoglobulin binding material from MHD may be responsible for apparent CH50 consumption in the presence of EDTA.