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Studies of phagocytosis in chronic granulomatous disease
Insights
Phagocyte function in chronic granulomatous disease (CGD) and myeloperoxidase (MPO) deficiency shows increased ingestion of antibody-coated targets. This suggests the hydrogen peroxide-MPO-halide system normally inhibits phagocytosis in healthy individuals.
Area of Science:
- Immunology
- Cell Biology
- Hematology
Background:
- Phagocyte dysfunction in chronic granulomatous disease (CGD) impairs bactericidal activity.
- Previous studies indicated normal organism ingestion but depressed C3b receptor (CR1) expression on polymorphonuclear leukocytes (PMNs) in CGD.
- Myeloperoxidase (MPO) deficiency is another condition affecting phagocyte function.
Purpose of the Study:
- To compare phagocytic activity of PMNs from CGD patients and MPO-deficient individuals with healthy controls.
- To investigate the role of the hydrogen peroxide (H2O2)-MPO-halide system in regulating PMN phagocytosis.
Main Methods:
- Examined PMN ingestion of sheep erythrocytes coated with IgG (E-IgG) or C3b/IgG (EAC3b-IgG).
- Assessed phagocytosis in CGD, MPO-deficient, and normal PMNs, with and without MPO inhibitors (sodium azide) or H2O2 scavengers (catalase).
- Evaluated Fc receptor (FcR) expression and rosette formation, and the effect of an H2O2-generating system.
Main Results:
- PMNs from CGD and MPO-deficient patients showed markedly increased ingestion of E-IgG and EAC3b-IgG compared to normals.
- Inhibiting MPO or scavenging H2O2 in normal PMNs significantly increased their phagocytic activity.
- CGD PMN phagocytosis remained elevated even with azide, and was abrogated by an H2O2-generating system, unlike MPO-deficient PMNs.
Conclusions:
- Cellular products of the H2O2-MPO-halide system down-regulate PMN phagocytic and rosette-forming activity in healthy individuals.
- This down-regulatory mechanism is impaired in CGD and MPO-deficient patients, leading to enhanced phagocytosis.
- Findings highlight a novel regulatory pathway for phagocyte function involving the H2O2-MPO-halide system.
Abstract:
Abnormal phagocyte function in chronic granulomatous disease (CGD) is associated with decreased bactericidal activity. Ingestion of serum-opsonized organisms is reported to be normal in these patients. We previously showed that in CGD the expression of C3b receptors (CR1) on polymorphonuclear leukocytes (PMNs) is significantly depressed. In this study, we compared the phagocytic activity of the PMNs from normal healthy controls with that of CGD patients and one individual with myeloperoxidase (MPO) deficiency. The ingestion of sheep erythrocytes (E) by PMNs adherent to a glass surface was examined; the E were coated either with excess IgG (E-IgG) or with C3b plus limited IgG (EAC3b-IgG). The PMNs, both in CGD and in MPO deficiency, ingested E-IgG and EAC3b-IgG at levels markedly above normal. C3b-coated erythrocytes were not phagocytosed. Preincubating the PMNs with sodium azide, which blocks MPO, or catalase, a scavenger of H2O2, caused a marked increase in phagocytosis by normal PMNs. Azide had a variable effect on PMN activity in CGD and no effect on the activity in the subject with MPO deficiency. Even in the presence of azide, the ingestion of EAC3b-IgG by the PMNs from the CGD patients was significantly greater than that seen in paired normals [mean phagocytic index (PI), 2.13 for CGD vs. 1.48 for normals; P less than 0.05 by the paired sample t test]. Similar results were obtained with ingestion of E-IgG. Notably, ingestion of serum-opsonized Candida organisms (relatively nondegradable particles) was markedly above normal with CGD PMNs and, in normal PMNs, azide treatment also evoked an increase. In addition, rosette formation of the adhered PMNs with E-IgG was enhanced with CGD and the azide-treated normal PMNs. We demonstrated that this increased activity was not the result of increased Fc receptor (FcR) number, as determined from the binding of a monoclonal anti-FcR antibody. Both the E-IgG rosette formation and the ingestion by CGD PMNs were abrogated in the presence of an H2O2-generating system. In contrast, the phagocytic activity of MPO-deficient PMNs was not altered by exogenous H2O2. These findings suggest that cellular products generated by the H2O2-MPO-halide system down-regulate the rosette-forming and phagocytic activity of PMNs from normal healthy individuals, but not that from CGD and MPO-deficient patients.