Inhibition of the lytic effect of guinea pig complement by rabbit complement.

A sensitized target cell, either a rat peritoneal mast cell or a sheep erythrocyte, when exposed to normal rabbit complement or heat-inactivated rabbit complement, becomes resistant to lysis by guinea pig complement. The inhibition of lysis observed by pretreatment of sensitized sheep erythrocytes with rabbit complement is due to a functional incompatibility between the EAC1ra4ra intermediate that is generated, and C2gp either functionally pure or in guinea pig complement. The second inhibitory mechanism, produced by heat-inactivated rabbit complement, is due to the action of an altered form of C1ra which retains its binding capacity for the sensitized site but is lytically unreactive.