Antigenic relationship between the fourth component of human and guinea pig complement.

Antigenic similarity between cell-bound human and guinea pig C4 was detected with antisera specific for each of these molecules. No cross-reaction could be detected between C4 of normal guinea pig or human sera or after treatment of the sera with antigen-antibody C1 complexes. The cross-reactivity between cell-bound human and guinea pig C4 may reflect conformational changes in the C4 molecule as a result of binding of the cell surface.