Histamine promotes the development of monocyte-derived dendritic cells and reduces tumor growth by targeting the myeloid NADPH oxidase.

The efficiency of immune-mediated clearance of cancer cells is hampered by immunosuppressive mediators in the malignant microenvironment, including NADPH oxidase-derived reactive oxygen species. We aimed at defining the effects of histamine, an inhibitor of the myeloid NADPH oxidase/NOX2, on the development of Ag-presenting dendritic cells (DCs) from myeloid precursors and the impact of these mechanisms for tumor growth. Histamine was found to promote the maturation of human DCs from monocytes by increasing the expression of HLA-DR and costimulatory molecules, which resulted in improved induction of Th cells with Th0 polarity.

The CD16-/CD56bright subset of NK cells is resistant to oxidant-induced cell death.

Phagocyte-derived reactive oxygen species ("oxygen radicals") have been ascribed a suppressive role in immunoregulation by inducing dysfunction and apoptotic cell death in lymphocytes. Earlier studies show that human NK cells are exceptionally sensitive to oxygen radical-induced apoptosis and functional inhibition. Two subsets of human CD56(+) NK cells have been identified: the highly cytotoxic CD56(dim) cells which constitute >90% of NK cells in peripheral blood, and the less cytotoxic but efficiently cytokine-producing CD56(bright) cells.

Activation of cytotoxic lymphocytes by interferon-alpha: role of oxygen radical-producing mononuclear phagocytes.

A significant part of the therapeutic benefit of interferon-alpha (IFN-alpha) therapy in malignant diseases and in chronic viral infections is assumed to result from activation of lymphocytes with natural killer (NK) and T cell phenotype. In tumor tissue and in chronically infected tissue, the function and viability of these lymphocytes are frequently impaired. Mononuclear phagocyte (MP)-derived reactive oxygen species (ROS) have been proposed to contribute to the lymphocyte suppression in these tissues.

Oxygen radical-induced natural killer cell dysfunction: role of myeloperoxidase and regulation by serotonin.

Natural killer (NK) cells are functionally suppressed and induced to apoptosis by reactive oxygen species (ROS) produced by mononuclear phagocytes (MPs). These inhibitory events are reversed by the biogenic amine serotonin. MPs generate hydrogen peroxide (H(2)O(2)), which is processed further by myeloperoxidase (MPO) to even more toxic compounds.

Histamine inhibits neutrophil NADPH oxidase activity triggered by the lipoxin A4 receptor-specific peptide agonist Trp-Lys-Tyr-Met-Val-Met.

The vasoactive amine histamine is found at high concentrations in the immune and inflammatory tissues. Earlier studies have revealed that histamine regulates the nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase-dependent formation of oxygen radicals by phagocytic cells. However, the effects of histamine on intracellular signal transduction mechanisms of relevance to oxidase regulation remain controversial.