Studies on immune adherence (C3b) receptor activity of human erythrocytes: relationship between receptor activity and membrane osmotic fragility.

Although human erythrocytes (E) possess C3b receptors (C3b-R), their in vivo functions are unknown. We had observed that E from patients with immune complex diseases had defective or impaired C3b-R activity when circulating immune complexes (CIC) could be demonstrated. This phenomenon has been investigated in relation to membrane osmotic fragility of such E by a coil planet centrifugation (CPC) system. Osmotic fragility was defined by the hemolysis starting point (HSP), peak point (HPP) and end point (HEP) using NaCl osmotic gradient (150-30 mOsM) coiled tubes. It was observed that E with low C3b-R activity showed high osmotic fragility. Hemolysis of E with low C3b-R activity started at 104 +/- 8 mOsM (n = 133) compared to 97 +/- 3 mOsM (n = 18) of patients' E with normal C3b-R activity and 96 +/- 5 mOsM of E from normal healthy donors (n = 128). Furthermore, we observed that HSP shifted towards lower osmolarity with clinical and immunological improvement of disease activity after treatment with corticosteroids. When osmotic gradients were lower to 120-50 mOsM, 52 out of 116 E samples with low C3b-R activity separated into 2 E populations. In contrast, none of 18 E samples with normal C3b-R activity separated into 2 E populations. However, we observed broadened fragility patterns in these 18 E samples. Serial studies of C3b-R activity, osmotic fragility and the presence of CIC were performed in 7 patients. Improvement of disease activity was associated with increased C3b-R activity, decreased osmotic fragility and the disappearance of CIC.(ABSTRACT TRUNCATED AT 250 WORDS)