Interacts with iC4 (methylamine-treated C4) but not for iC3 (methylamine-treated C3). Predominantly found in association with the membrane fraction, but also located in the cytoplasm and in the supernatant. Expressed in fetal liver and to a lesser extent in fetal spleen and thymus. Expression appears to be limited to hematopoietic and fetal lymphoid tissue. Belongs to the receptors of complement activation (RCA) family.