Complementation in monocyte hybrids revealing genetic heterogeneity in chronic granulomatous disease

Abstract

Chronic granulomatous disease (CGD) is a rare syndrome, found predominantly in male children and characterized by life-threatening, recurrent infections. The Superoxide (O₂⁻)/hydrogen peroxide (H₂O₂) generating system in the granulocytes and monocytes of CGD patients is completely defective¹. Furthermore, a novel type of cytochrome b, detected by the optical spectrum of phagocytes from healthy subjects^2,3, is lacking in those of most male CGD patients⁴. In female CGD patients, the cytochrome b is present⁴, but cannot, as in normal cells⁵, be reduced on metabolic stimulation of the phagocytes in anaerobic conditions. Here, to demonstrate the importance of cytochrome b in this system and to investigate the genetic background of the various forms of CGD, we have hybridized monocytes from a cytochrome b negative, X-linked male CGD patient with monocytes from a cytochrome b positive, male CGD patient with unknown genetic background. Monocytes were used because they are the only blood phagocytes that show an active protein synthesis, whereas fibroblasts or lymphocytes do not express the O₂⁻/H₂O₂ generating system. The heterologous hybrids were positive in the nitroblue tetrazolium (NBT) slide test, indicating the complementation of the O₂⁻/H₂O₂ generating system, whereas the homologous hybrids remained negative, as did the non-fused cells of these patients. We thus conclude that cytochrome b is part of the O₂⁻/H₂O₂ generating system and that somatic cell hybridization experiments with monocytes provide a means of studying the genetic background of CGD patients. We believe this to be the first report of genetic complementation by somatic cell hybridization experiments using monocytes instead of fibroblasts.