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Complementation in monocyte hybrids revealing genetic heterogeneity in chronic granulomatous disease
Insights
Somatic cell hybridization of monocytes demonstrated that cytochrome b is crucial for the superoxide (O2-)/hydrogen peroxide (H2O2) generating system in Chronic Granulomatous Disease (CGD). This technique aids in studying CGD
Area of Science:
- Immunology
- Genetics
- Cell Biology
Background:
- Chronic Granulomatous Disease (CGD) is a rare genetic disorder causing severe recurrent infections due to a defective superoxide (O2-)/hydrogen peroxide (H2O2) generating system in phagocytes.
- A specific cytochrome b is absent in most male CGD patients and non-functional in female CGD patients, highlighting its importance in the O2-/H2O2 generating system.
Purpose of the Study:
- To investigate the role of cytochrome b in the O2-/H2O2 generating system of phagocytes.
- To explore the genetic basis of different forms of CGD using somatic cell hybridization.
- To demonstrate the utility of monocyte hybridization for studying CGD genetics.
Main Methods:
- Monocytes from a cytochrome b-negative X-linked CGD patient were hybridized with monocytes from a cytochrome b-positive CGD patient.
- Monocytes were chosen for their active protein synthesis and expression of the O2-/H2O2 generating system.
- The nitroblue tetrazolium (NBT) slide test was used to assess the O2-/H2O2 generating capacity of the hybrid cells.
Main Results:
- Heterologous monocyte hybrids (from different CGD patients) showed restored O2-/H2O2 generation, indicated by a positive NBT test.
- Homologous hybrids (from the same patient) and non-fused cells remained negative in the NBT test, confirming the complementation was due to the fusion of cells with different genetic defects.
- These results confirm that cytochrome b is an integral component of the O2-/H2O2 generating system.
Conclusions:
- Cytochrome b is essential for the O2-/H2O2 generating system in phagocytes.
- Somatic cell hybridization using monocytes is an effective method for studying the genetic complementation and background of CGD.
- This study represents the first report of genetic complementation using monocyte hybridization in CGD research.
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 defective. Furthermore, a novel type of cytochrome b, detected by the optical spectrum of phagocytes from healthy subjects, is lacking in those of most male CGD patients. In female CGD patients, the cytochrome b is present, but cannot, as in normal cells, 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.