FcIgG and C3 (CR1 and CR3) receptors are responsible for binding opsonized particles, phagocytosis, and immune adherence reactions by circulating and tissue-fixed mononuclear phagocytes. Alterations in the expression of these receptors may thus significantly influence the function of these cells. Because chemoattractants have been shown to both recruit and modulate the function of monocytes, this study specifically examines the effects of human C5a and N-formyl-methionyl-leucyl-phenyl-alanine (FMLP) on human peripheral blood monocyte FcIgG and C3 receptor expression in vitro. Adherent, elutriator-purified monocytes were incubated with C5a (10-7 to 10-10 M) or FMLP (10-5 to 10-10 M) for 30 min at 37°C, and FcIgG receptor expression was assessed by rosetting with sheep erythrocytes sensitized with limiting dilutions of IgG. Human C5a caused dose-related increases in Fc rosettes of 28% at 10-9 M, 63% at 10-8 M, and 167% at 10-7 M (p < 0.01). In contrast, no significant increases in monocyte Fc receptor expression were induced by FMLP. Similar rosetting experiments were performed with sheep erythrocytes opsonized with limiting amounts of human C3b to assess C3b receptor expression on adherent human monocytes stimulated with C5a (10-7 to 10-10 M) or FMLP (10-6 to 10-9 M) for 30 min at 37°C. Again, human C5a caused dose-related increases in monocyte C3b rosette formation; at 10-8 M and 10-7 M concentrations of C5a, these increases equaled 119% and 196%, respectively (p < 0.05). In these experiments, 10-6 M FMLP also caused a significant increase of 110% in monocyte C3b rosette formation (p < 0.05). Modulation of monocyte cell surface receptors by human C5a or FMLP was also examined by measuring cell fluorescence and side scatter by dual channel flow cytometry after staining normal leukocytes in citrated venous blood with receptor-specific monoclonal antibodies. These flow cytometric studies demonstrated that both C5a and FMLP induce dose-related increases in CR1 (C3b receptor) and CR3 (iC3b receptor) expression in both monocytes and neutrophils. The ranges of increased mean channel fluorescence of CR1 on monocytes were 64 to 111% (C5a 2 x 10-9 M to 2 x 10-8 M) and 38 to 114% (FMLP 2 x 10-9 to 2 x 10-6 M); CR3 expression on monocytes was also enhanced with mean channel fluorescence increases of 78 to 123% (C5a 2 x 10-9 to 2 x 10-8 M) and 54 to 105% (FMLP 2 x 10-9 to 2 x 10-6 M). These findings were confirmed by additional cytometric studies employing multi-parameter analysis of stimulated monocytes in peripheral blood which were double-stained with antibodies directed against these respective C3 receptors and Leu-M3. Kinetic studies revealed that enhanced C3 receptor expression began within 1 min of stimulation with C5a and reached plateau within 20 min. These experiments indicate that human C5a and other soluble mediators may quickly - and in some cases selectively - modulate leukocyte receptor expression, and thus may significantly influence effector functions of these cells.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Immunology|
|State||Published - 1985|
ASJC Scopus subject areas
- Immunology and Allergy