Human diseases associated with C3 receptor deficiencies.

Genetic deficiencies of complement receptors have recently been described. CR1 expression is reduced on erythrocytes, leucocytes and podocytes of many patients with systemic lupus erythematosus because of both genetic and acquired mechanisms. CR1 deficiency is also found in AIDS and AIDS-related syndromes and correlates with clinical subpopulations of HIV-infected patients. The pathogenic significance of CR1 deficiency relates to the functions of CR1 in clearance of immune complexes, phagocytosis and immune regulation. CR3 deficiency occurs as an autosomal recessive inherited disease characterized by the lack of or severe reduction in expression of the leucocyte antigens CR3, LFA1, p150,95 and their common chain. The disease is associated with severe defects in neutrophil and lymphocyte functions and recurrent bacterial infections. The in vivo effects of C3 receptor deficiencies emphasize the critical role of these membrane molecules in immunity.