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Two homologous high-affinity receptors for the chemoattractant interleukin-8, IL-8RA and IL-8RB, and one for the chemoattractant C5a (C5aR) have been cloned. These membrane proteins are members of the rhodopsin superfamily of G-protein coupled seven-transmembrane segment receptors. New monoclonal antibodies (mAb) directed against the deduced N-terminal sequences of the IL-8RA (mAb SE2) and IL-8RB (mAb HC2) were generated to determine the IL-8R expression on human blood leukocytes and two human myeloid cell lines. The C5aR expression was detected using the mAb W17/1. Approximately 107,000 C5aR, 55,000 IL-8RA, and 25,000 IL-8RB molecules per cell could be detected on human granulocytes by flow cytometric analysis. On peripheral blood monocytes, 42,000 C5aR molecules/cell and 3000 IL-8RB molecules/cell were expressed. However, we were unable to quantitate IL-8RA expression, which was detectable but below 2500 molecules per cell and thus outside the standard range for the quantitation of receptor molecules by flow cytometry. On AML-193 cells, only the IL-8RB was constitutively expressed, whereas on HL-60 cells, we could not detect expression of any of the three receptors. Vitamin D3 (250 ng/ml, 7 days), which has been shown to induce differentiation of AML-193 and HL-60 cells into the monocytic phenotype, led to an up-regulation of IL-8RB and C5aR in both cell lines in the absence of any expression of IL-8RA. In contrast, all-trans retinoic acid (0.1 microM, 7 days), which induces differentiation into the granulocytic phenotype, led to an up-regulation of IL-8RB in AML-193 cells and to an expression of IL-8RB and C5aR in HL-60 cells. Again, neither cell line expressed IL-8RA. These findings suggest that regulation of IL-8RA expression differs from that of its IL-8RB homolog and may be a late event in leukocyte maturation.

Our previous studies demonstrated that monocytes, when cultured under certain conditions, are able to differentiate into DC-like cells (MoDC) presenting a high accessory activity and low phagocytic function. In the present study, we demonstrate that under the effect of a triple combination of IL-4, IFN-gamma and GM-CSF human blood monocytes are able to differentiate into the cells expressing an identical phenotype and functional features of blood dendritic cells. MoDC stimulated T cell proliferation 20-30 times higher than untreated monocytes, similar to blood DC. They expressed abundant HLA-DR molecules, but only trace amounts of the monocyte/macrophage markers CD16 (FcR III), CD32 (FcR II), and CD14. Phagocytosis of Ig- and complement-opsonized bacteria was reduced by 93%.

Infection of murine PU5-1.8 macrophages and human monocytes by influenza A virus was associated with virus replication, release of tumor necrosis factor-alpha (TNF-alpha) and subsequent cell death. In the presence of small and by itself rather inefficient concentrations of lipopolysaccharide (LPS) or free lipid A (1 to 10 ng/ml), TNF-alpha production of virus-infected macrophages was strongly potentiated. LPS-triggered and enhanced TNF-alpha release from virus-infected macrophages was neither due to increased cell survival nor altered virus replication, potentiated TNF-alpha gene transcription, release of intracellularly stored TNF-alpha or shifts in the kinetics of TNF-alpha secretion. Influenza A virus infection alone induced a massive TNF-alpha mRNA accumulation which, however, was only weakly translated into bioactive TNF-alpha protein. When these virus-primed macrophages were exposed to LPS either simultaneously or up to 4 h after infection, an efficient and high translation into TNF-alpha protein occurred. Although the LPS-induced biochemical pathways leading to an augmented TNF-alpha production by virus-infected macrophages still remains unsolved, the findings suggest that the frequently observed serious clinical complications in the course of combined influenza A virus and bacterial infections may be due, at least in part, to an excessive release of cytokines such as TNF-alpha.