Persistence of Ia antigen and antigen-presenting activity by cultured human monocytes

Cardiac myofibroblast induces decreased expression of major histocompatibility complex class II (Ia) on rat monocyte/macrophages

The up-regulation of HLA antigens is important during heart inflammatory events and myofibroblasts may modulate the expression of this molecule in tissues. To test this possibility, the effect of cardiac myofibroblast:macrophage contact and the production of myofibroblast inhibitor factor(s) on the macrophage HLA (Ia) expression were studied. Listeria monocytogenes-elicited Ia + peritoneal macrophages (high Ia expression) were co-cultured with cardiac myofibroblasts for 3 and 7 days (myofibroblast contact). Proteosa peptone-elicited macrophages (low Ia expression) were cultured for 3 days with interferon gamma (INF-γ) and myofibroblast conditioned medium (FCM). Ia expression was analyzed by immunofluorescence and by radioimmune assay. Myofibroblast contact induced decreased expression of Ia molecule on macrophages (p < 0.001). This was confirmed by the radioimmune analysis in macrophage: myofibroblast co-cultures (p < 0.001). Double staining for Ia and CD14 showed that only CD14 positive cells (macrophages) expressed Ia molecule. FCM was capable of diminishing Ia expression induced by INF-γ on macrophages (p < 0.001). Decreased Ia macrophage expression induced by myofibroblasts could be important in the heart inflammation's resolution, probably involving Ia redistribution on cell: cell contact and myofibroblast inhibitor factor production.

Species-dependent regulation of monocyte/macrophage Ia antigen expression and antigen presentation by prostaglandin E

The expression of Ia antigen by various murine and human macrophage populations and the ability of prostaglandins of the E series to regulate Ia antigen expression were explored. Monocytes and macrophages from human and murine populations demonstrated a dichotomy in the expression of Ia antigen. Both human monocytes and macrophages expressed elevated levels of Ia antigen compared to their murine counterpart. Murine macrophages appear to express elevated levels of Ia antigen only when actively interacting with T lymphocytes in vivo or with lymphokines in vitro. Prostaglandins of the E series can suppress murine macrophage Ia antigen expression, but have little effect on the expression of Ia antigen by human monocytes and macrophages. Also, prostaglandins of the E series do not modulate the ability of human monocytes to present antigen to autologous lymphocytes when studied over a broad concentration range. These data suggest that prostaglandin E compounds do not profoundly affect human monocyte/macrophage Ia antigen expression or human monocyte antigen presenting activity.

Decrease of HLA-DR antigen expression by human monocytes during cultivation in absence of exogenous or endogenous interferon-gamma

The kinetics of HLA-DR antigen expression by human peripheral blood monocytes during cultivation in vitro was studied. Immediately after separation by glass adherence, about 60% of monocytes expressed DR antigens as judged by indirect fluorescence staining with a monoclonal antibody (BL-DR/1). Monocytes carefully depleted of lymphocytes, gradually lost their DR antigens during cultivation in the absence of exogenous interferon-gamma (IFN-gamma). However, addition of a few lymphocytes to the adherent cells prevented the decrease of DR antigen expression. Furthermore, it was shown that doses as low as 1 IU/ml of IFN-gamma are sufficient to induce DR antigen expression by cultured monocytes. Experiments with cyclosporin A suggest that lymphocytes contaminating the monocyte preparations can produce spontaneously sufficient amounts of IFN-gamma for maintenance of the DR antigens on monocytes.

Dissociation among Ia antigen expression, accessory cell function, and antigen processing in two acute monoblastic leukemia lines

To better understand the role of Ia antigen expression, accessory cell function, and antigen ingestion in antigen presentation and the initiation of T cell proliferation, we studied these events in two acute monoblastic leukemia (AMoL) lines. The cell lines were positive for surface Ia antigen; one stimulated proliferation of the allogeneic mononuclear cells in mixed lymphocyte culture and culture supernatants from the other line contained interleukin 1 (IL-1) when tested for comitogen activity in a standard mouse thymocyte assay. The AMoL cells also contributed accessory factors for mitogen-induced proliferative responses by T cells. High numbers of cells of one of the lines tended to suppress mitogen induced T cell proliferation. Irradiated trinitrophenylated AMoL cells were able to stimulate TNP-specific HLA-DR matched T cell blasts to proliferate. However, when irradiated AMoL cells were cultured with a protein antigen (tetanus toxoid or varicella zoster) plus antigen-specific parental T cell blasts, antigen presentation failed to occur. Diminished phagocytosis by the AMoL cells, together with reduced catabolism of labelled antigen, is a likely explanation for this finding. Our results demonstrate that the concurrent presence of a complex protein antigen and Ia-positive monocytic leukemia cells capable of accessory function is alone insufficient to maintain antigen-specific T cell proliferation. Moreover, these findings suggest that antigen processing, involving ingestion and reexpression of antigenic determinants, is an essential aspect of antigen presentation not tightly linked to Ia antigen expression or IL-1 production in these AMoL lines.