A monoclonal antibody to sialophorin (CD43) induces homotypic adhesion and activation of human monocytes

Treatment of human monocytes for 24-48 h with the anti-CD43 mAb L10 caused five- to sevenfold stimulation of hydrogen peroxide-producing capacity, an established characteristic of activated monocytes. Peroxide-producing capacity induced by L10 antibody (1.6 +/- 0.3 nmol H2O2/micrograms DNA/h) was comparable with that induced by IFN-gamma (1.3 +/- 0.4 nmol H2O2/micrograms DNA/h), but appeared more rapidly (maximal at 24 h) than in the IFN-gamma-treated monocytes (maximal at 48 h). Treatment of monocytes with L10 mAb also caused dramatic increase in aggregation (homotypic adhesion). Induction of monocyte aggregation by L10 mAb required incubation for 1-8 h in the presence of Mg2+ and was abrogated by TA-1, an anti-LFA-1-alpha mAb. Thus, L10-induced monocyte activation proceeds via a Mg2+-requiring aggregation stage involving LFA-1. Whereas the extent of monocyte aggregation induced by L10 mAb and by IFN-gamma were comparable, the L10-induced aggregation occurred more rapidly (maximal at 8 h) than the IFN-gamma-induced aggregation (maximal at 24 h). The more rapid appearance of aggregation and increased hydrogen peroxide capacity in L10-treated monocytes suggests that the L10-induced activation pathway is independent of IFN-gamma-and IFN-gamma-R dependent events. These findings suggest that the surface molecule CD43 is the receptor of an independent activation pathway that leads in lymphocytes to proliferation and in monocytes to activation.

Peptides encoded by the calcitonin gene inhibit macrophage function

Neuropeptides are considered to play an important role in the modulation of a number of immune functions. Calcitonin gene-related peptide (CGRP), one of the neuropeptides, was found to profoundly inhibit the ability of macrophages to produce H2O2 in response to IFN-gamma or to act as APC. For the inhibition of H2O2 production to occur, preincubation of the macrophages with CGRP was required. Among neuropeptides that are similar in size, calcitonin also prevented macrophage activation but adrenocorticotropic hormone did not. These findings suggest that CGRP and calcitonin play an important role in modulating the ability of macrophages to present Ag and to respond to activating factors.

Peptides encoded by the calcitonin gene inhibit macrophage function

Neuropeptides are considered to play an important role in the modulation of a number of immune functions. Calcitonin gene-related peptide (CGRP), one of the neuropeptides, was found to profoundly inhibit the ability of macrophages to produce H2O2 in response to IFN-gamma or to act as APC. For the inhibition of H2O2 production to occur, preincubation of the macrophages with CGRP was required. Among neuropeptides that are similar in size, calcitonin also prevented macrophage activation but adrenocorticotropic hormone did not. These findings suggest that CGRP and calcitonin play an important role in modulating the ability of macrophages to present Ag and to respond to activating factors.

IFN-gamma, tumor necrosis factor-alpha, and urokinase regulate the expression of urokinase receptors on human monocytes

The ability of macrophages to reach inflammatory loci is crucial in the function of cellular immunity. Invasive properties of macrophages may be due to the proteinase urokinase which binds to cell surface receptors, and thereby confers on macrophages the capacity for localized proteolysis of the interstitium. Here, we investigated the role of the macrophage-activating factors IFN-gamma, TNF-alpha, and granulocyte-macrophage-CSF and of urokinase on the expression of urokinase receptors by human cultured monocytes. IFN-gamma and TNF-alpha induced increased urokinase binding to human cultured monocytes in a time- and dose-dependent fashion. At optimal concentrations, IFN-gamma (200 U/ml) increased the number of receptors/cell from 14,000 to 64,000, TNF-alpha (50 U/ml) to 30,000, and combinations of IFN-gamma and TNF-alpha to 90,000. Granulocyte-macrophage-CSF had no effect. The enhanced urokinase binding is due to increased numbers of urokinase receptors and not an increased affinity of the receptor for urokinase. In the presence of urokinase during monocyte activation, IFN-gamma induced only 25,000 receptors/cell. However, urokinase does not inhibit increased receptor expression when the cells are activated with TNF-alpha. The effect of urokinase on induction of urokinase receptors by combinations of IFN-gamma and TNF-alpha varied with the dosage of TNF-alpha: A combination of IFN-gamma (200 U/ml) and TNF-alpha (15 U/ml) induced 38,000 receptors/cell in the presence and 90,000 receptors/cells in the absence of urokinase, whereas IFN-gamma (200 U/ml) and TNF-alpha (20 U/ml) induced 90,000 receptors/cell in the absence and presence of urokinase. These studies demonstrate that IFN-gamma, TNF-alpha, and urokinase collectively regulate the number of urokinase receptors on human monocytes. The induction of urokinase receptors may be responsible for increased invasiveness of the activated macrophage.

IFN-gamma, tumor necrosis factor-alpha, and urokinase regulate the expression of urokinase receptors on human monocytes

The ability of macrophages to reach inflammatory loci is crucial in the function of cellular immunity. Invasive properties of macrophages may be due to the proteinase urokinase which binds to cell surface receptors, and thereby confers on macrophages the capacity for localized proteolysis of the interstitium. Here, we investigated the role of the macrophage-activating factors IFN-gamma, TNF-alpha, and granulocyte-macrophage-CSF and of urokinase on the expression of urokinase receptors by human cultured monocytes. IFN-gamma and TNF-alpha induced increased urokinase binding to human cultured monocytes in a time- and dose-dependent fashion. At optimal concentrations, IFN-gamma (200 U/ml) increased the number of receptors/cell from 14,000 to 64,000, TNF-alpha (50 U/ml) to 30,000, and combinations of IFN-gamma and TNF-alpha to 90,000. Granulocyte-macrophage-CSF had no effect. The enhanced urokinase binding is due to increased numbers of urokinase receptors and not an increased affinity of the receptor for urokinase. In the presence of urokinase during monocyte activation, IFN-gamma induced only 25,000 receptors/cell. However, urokinase does not inhibit increased receptor expression when the cells are activated with TNF-alpha. The effect of urokinase on induction of urokinase receptors by combinations of IFN-gamma and TNF-alpha varied with the dosage of TNF-alpha: A combination of IFN-gamma (200 U/ml) and TNF-alpha (15 U/ml) induced 38,000 receptors/cell in the presence and 90,000 receptors/cells in the absence of urokinase, whereas IFN-gamma (200 U/ml) and TNF-alpha (20 U/ml) induced 90,000 receptors/cell in the absence and presence of urokinase. These studies demonstrate that IFN-gamma, TNF-alpha, and urokinase collectively regulate the number of urokinase receptors on human monocytes. The induction of urokinase receptors may be responsible for increased invasiveness of the activated macrophage.