Inhibition of release of arachidonic acid, superoxide, and IL-1 from human monocytes by monoclonal anti-HLA class II antibodies: effects at proximal and distal points of inositol phospholipid hydrolysis pathway

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Circulating CD2+ Monocytes Are Dendritic Cells

Low levels of CD2 have been described on subsets of monocytes, macrophages, and dendritic cells. CD2 is expressed on about one-third of circulating monocytes, at levels one-half log lower than on T or NK cells, representing 2–4% of PBMC. FACS analysis of CD2+ and CD2− monocytes revealed no significant difference in the expression of adhesion molecules (CD11a/b/c), class II Ags (HLA-DR, -DQ, -DP), myeloid Ags (CD13, CD14, CD33), or costimulatory molecules (CD80, CD86). Freshly isolated CD2+ and CD2− monocytes were morphologically indistinguishable by phase contrast microscopy. However, scanning electron microscopy revealed large prominent ruffles on CD2+ monocytes in contrast to small knob-like projections on CD2− monocytes. After 2 days of culture, the CD2+ monocytes largely lost CD14 expression and developed distinct dendrites, whereas the CD2− monocytes retained surface CD14 and remained round or oval. Freshly isolated CD2+ monocytes were more potent inducers of the allogeneic MLR and more efficiently induced proliferation of naive T cells in the presence of HIV-1 gp120 than did CD2− monocytes. After culture in the presence of GM/CSF and IL-4, CD2+ monocytes were up to 40-fold more potent than monocyte-derived dendritic cells or CD2− monocytes at inducing allogeneic T cell proliferation. These findings suggest that circulating CD2+ and CD2− monocytes are dendritic cells and the precursors of macrophages, respectively. Thus, dendritic cells are far more abundant in the blood than previously thought, and they and precursors of macrophages exist in the circulation as phenotypically, morphologically, and functionally distinct monocyte populations.

Modulation of HLA-DR antigen and ICAM-1 molecule expression on airway epithelial cells by sodium nedocromil

OBJECTIVE

To test in vitro and in vivo the hypothesis that sodium nedocromil could modulate the expression of surface molecules on airway epithelial cells.

METHODS

Human bronchial epithelial cells, obtained from surgically resected bronchi, were cultured and stimulated with recombinant IFN-gamma in the presence of sodium nedocromil. The intensity of the expression of surface molecules HLA-DR and ICAM-1 molecules on bronchial epithelial cells in vitro, was quantified by specific antibody staining and flow-cytometry analysis. Furthermore, we studied the effect of the drug on airway inflammation in vivo and on allergic rhinitis patients sensitized to house dust mites. Nasal epithelial cells were collected by brushing, at baseline and 2 to 3 weeks after treatment with sodium nedocromil. The expression of HLA-DR and ICAM-1 molecules was measured by flow-cytometry, and the proportions of neutrophils and eosinophils "contaminating" the epithelial cells evaluated by light microscopy examination of nasal brushings.

RESULTS

The enhanced HLA-DR and ICAM-1 expression, induced by IFN-gamma, was effectively downregulated, in a dose-dependent manner, by sodium nedocromil. At all the concentrations tested (10(-9) to 10(-4) M), the inhibitory activity of the drug was stronger on HLA-DR than on ICAM-1 expression (P<.05, all comparisons). As compared with healthy subjects, patients with allergic rhinitis had a higher expression of HLA-DR (P<.05) but not of ICAM-1 molecules (P>.05) on nasal epithelial cells, and higher proportions of nasal eosinophils (P<.05). Treatment with sodium nedocromil downregulated the expression of HLA-DR (P<.05), but not of ICAM-1 (P>.05), and induced a mild, but not statistically significant, decrease of nasal eosinophilia (P>.05).

CONCLUSION

These data demonstrate that the antiinflammatory activity of sodium nedocromil may include modulation of surface molecule expression on airway epithelial cells.

HLA-DR and ICAM-1 expression on bronchial epithelial cells in asthma and chronic bronchitis

HLA-DR and ICAM-I molecules play an important role in cellular interactions, and their expression can be induced by inflammatory stimuli. We evaluated the spontaneous expression of HLA-DR and ICAM-1 on epithelial cells obtained by bronchial brushing from 27 asthmatic patients, 10 chronic bronchitis (CB) patients, and 19 normal subjects. In all cases > 90% pure epithelial cells were obtained. HLA-DR and ICAM-1 were characterized using monoclonal antibodies and revealed by immunocytochemistry (APAAP technique). In asthma, the percentage of cells expressing HLA-DR and ICAM-1 was significantly increased by comparison with normal values (p < 0.001) and GB (p < 0.001; HLA-DR; p < 0.003; ICAM-1) and was correlated with the clinical score of Aas (p < 0.001, HLA-DR; p < 0.001, ICAM-1) and the FEV1 (p < 0.001, HLA-DR; p < 0.002; ICAM-1). In CB, expression of both markers was slightly but significantly increased by comparison with normal subjects and was correlated with FEV1 (p < 0.02, HLA-DR; p < 0.03, ICAM-1). In addition, the expression of HLA-DR and ICAM-1 was significantly correlated. This study suggests that epithelial cells are in an activated state in asthma and that the extent of expression of these markers may be specific to asthma, not a general feature of chronic inflammation.