A complement inhibitor produced by Stachybotrys complementi, nov. sp. K-76, a new species of fungi imperfecti.

A complement inhibitor, K-76, was isolated and purified from the culture supernatant of a fungus, Stachybotrys complementi, nov. sp. K-76, isolated from soil of Ishigaki Island, Okinawa. K-76 is a sesquiterpene compound and it can be oxidized to a monocarboxylic derivative (K-76 COOH), the sodium salt of which is very soluble and much less toxic than K-76. K-76 and K-76 COOH both inhibited complement activation by either the classical or alternative pathway. They inhibited generation of the factor chemotactic to human polymorphonuclear leukocytes from human serum by aggregated immunoglobulin. When sensitized erythrocytes were treated with complement in the presence of K-76 COOH, the resulting unlysed cells were found to be in the state of EACl, 4b, 2a, 3b. Thus K-76 COOH is considered to block mainly the C5 intermediate step. K-76 COOH did not inhibit any proteases or esterases tested, except when tested at high concentration.