Precipitin test negative farmer's lung—activation of the alternative pathway of complement by mouldy hay dusts

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Abstract
Summary: Respirable fractions of mouldy hay and grain dusts were incubated with fresh human serum, Immunoelectrophoresis against rabbit anti C3 activator serum showed a conversion of C3 proactivator to C3 activator indicating that these respirable dust fractions are capable of operating the C3 by‐pass mechanism (alternative pathway). It is suggested that this, or other mechanisms, may contribute towards a disease essentially the same as classical immune complex farmer's lung where exposure is sufficiently heavy.