EVALUATION OF THE ROLE OF FC-GAMMA AND COMPLEMENT RECEPTORS IN THE DECREASED PHAGOCYTOSIS OF HEREDITARY HEMOCHROMATOSIS PATIENTS

Hereditary haemochromatosis (HH) monocytes have a decreased antibody m ediated phagocytosis of rabbit erythrocytes and Staphylococcus aureus compared to control monocytes. In order to investigate whether this de crease could be attributed to a different level of expression of Fc ga mma receptors (Fc gamma R) or complement receptors (CR), which coopera te even in the absence of complement, the surface expression of these receptors was determined on monocyte-enriched suspensions. In contrast to what was expected, HH monocytes displayed a significantly higher l evel of Fc gamma RI and Fc gamma RIIa as compared to healthy donor mon ocytes, but these differences were very small. The expression of the o ther receptors studied were similar for both groups. The heat-inactiva ted mouse serum used for opsonizing the erythrocytes mainly contained mouse IgG1. Two genetically different forms of Fc gamma RIIa are known , each with a different affinity for mouse IgG1 antibodies. Therefore, the Fc gamma RIIa polymorphism in monocytes (MN) of both groups was a lso investigated. A similar distribution was found for patients and he althy donors. In addition, the extent of erythrophagocytosis of both d onors and patients was independent of Fc gamma RIIa allotype. Our resu lts indicate that the altered phagocytosis by HH monocytes cannot be a ttributed to a different level of expression of receptors involved in phagocytosis or to Fc gamma RIIa polymorphism.