Regulation of the binding of C3-coated particles to human lymphocytes by human complement component H

Human complement component H was found to modify greatly the binding of C3-coated particles to lymphocytes. We used an experimental model in which lymphocytes were mixed successively with various amounts of H and C3b-coated erythrocytes. At least three mechanisms were postulated to interpret the phenomenon: (i) release of endogenous I by lymphocytes triggered by H through specific binding sites, (ii) cleavage of iC3b by I, promoted by complement receptor type one, and (iii) inhibition of immune adherence by H. Such qualitative and quantitative changes in C3-coated particle recognition by the binding sites might mediate important functions of lymphocytes.