Levels of complement factors in human serum during immediate and late asthmatic reactions and during acute hypersensitivity pneumonitis.

In 16 asthmatic patients and in four subjects suspected of having hypersensitivity pneumonitis, serum levels of CH50, C3, C4, C5 and factor B were measured before, between 10 and 20 min, between 5 and 7 h and, in the latter group, also 24 h after allergen challenges provoking type I bronchial reactions or acute hypersensitivity pneumonitis. There was a significant decrease in one of the complement factors in two patients during the immediate asthmatic phase, but in no patient during the late asthmatic phase and in no patient with hypersensitivity pneumonitis. On the other hand, significant increases of C3, C4, and/or CH50 were seen in five patients during immediate asthmatic reactions, in seven patients during late asthmatic reactions and in all cases with hypersensitivity pneumonitis. However, with respect to the particular complement factors the vast majority of the patients showed no appreciable change. Investigations of C3 split products, which were done in seven patients gave negative results. No correlations existed between the changes in the levels of complement factors to increases of Raw, decreases of DLCO, size of skin test reactions or RAST scores. The cause and pathophysiological role of the non-uniform behaviour of serum complement levels after inhalation challenges is not yet clear; obviously both consumption and formation of complement factors take place during allergen-induced asthmatic reactions and hypersensitivity pneumonitis.