The effect of soluble material from mouldy hay dust on the complement system

The soluble material derived from the respirable fraction of mouldy hay dust has anti-complementary as well as enzyme activity. The anti-complementary activity resides in a heavy molecular weight fraction (approx. 800,000) and acts directly on C1 without combination with or alteration of IgG or IgM. The enzyme function has a lower molecular weight (approx. 30,000-38,000) and is related to papain in that IgG is split into two distinct components of similar molecular weight and with antigenic determinants the same as Fab and Fc pieces respectively. C1 activation leads to C3-9 depletion and on a per sample basis it is calculated that the soluble mouldy hay dust material is up to sixty-six times more active at C3-9 activation than the particulate material in mouldy hay dust. It is probable that the capacity to activate C1 resides in other dusts and may be a basis for non-immune histamine release in the lungs when such a dust is inhaled. It is also probable that non-specific skin reactions are related to C1 activation. The finding of an enzyme with papain-like activity is significant since the introduction of papain into the lungs of the experimental animal leads to emphysema and this has been described as a feature of farmer's lung.