Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/1996
Publication Date: N/A
Interpretive Summary: Mononuclear phagocytes are one type of white blood cell often involved in the early immune response to infectious disease organisms. These cells have several functions, one is the production of soluble factors that, when released after the cells have become activated, kill microorganisms. One such factor is nitric oxide, and it has been shown to be produced and released from mouse macrophages. However, the production of nitric oxide from mononuclear phagocytes obtained from other species, including humans, has been controversial. In this study, we have demonstrated that monocytes, a circulating mononuclear phagocyte, obtained from the blood stream and spleen of cattle can be activated for the induction of nitric oxide production. It was also demonstrated that neutrophils, another type of white blood cell are not programmed for this production. This study is important for a better understanding of what constitutes a successful immune response in cattle against invading pathogens. One such organism i Babesia bovis, a protozoan (one-celled animal) that causes a serious disease in cattle, and the target pathogen in our overall plans to develop an improved vaccine. We have evidence to suggest that this parasite is susceptible to the effects of nitric oxide, which implies that the activation of mononuclear phagocytes will be an important element in the design of the vaccine.
Technical Abstract: Microbicidal activity of reactive oxygen intermediates and reactive nitrogen intermediates has been described from murine and human cytokine activated macrophages. An L-arginine-dependent pathway of nitric oxide generation has been described from bovine bone marrow-derived and monocyte- derived macrophages in response to a phagocytic stimulus. We investigated the induction and release of both reactive oxygen intermediates and reactive nitrogen intermediates from bovine neutrophils, and blood and spleen mononuclear phagocytes in response to either a phagocytic or cytokine stimulus. Mononuclear phagocytes were poor producers of hydrogen peroxide (reactive oxygen intermediate) under conditions that readily caused release by neutrophils. IN contrast, nitrite, as a measure of nitric oxide production, could not be induced from neutrophils under any stimulation conditions, while mononuclear phagocytes responded to both a phagocytic stimulus and cytokines with the induction of nitric oxide synthase message and production and release of nitrite. There appeared to be two populations of monocytes that differed both in their adherent characteristics and their level of cytokine-induced nitric oxide production. Both populations stained with a single monoclonal antibody. However, the population that had not adhered to plastic within 3 hours produced up to 3 times more nitric oxide on a per cell basis than the readily adherent population in response to cytokine stimulation. Cytokine induction required interferon-gamma as a priming stimulus for subsequent triggering by either tumor necrosis factor-alpha or lipopolysaccharide. L- arginine dependence was demonstrated by inhibition with an L-arginine analog and restoration with addition of excess exogenous L-arginine.