Gomis, S.Godson, D.Wobeser, G.Potter, A.2024-09-052024-09-051997-11-22Proceedings and Abstract of the Annual Research Sessions, November 22, 1997, University of Peradeniya, Sri Lanka pp 164-165955-589-015-3https://ir.lib.pdn.ac.lk/handle/20.500.14444/695The interaction between bovine mononuclear phagocytes (BMP) and Haemophilus somnus are known to be complex. Using a flow cytometric phagocytosis assay, it was found that logarithmically growing H somnus significantly inhibited the phagocytosis of opsonized S. aureus by bovine alveolar macrophages (BAM) obtained both from healthy calves and from cattle experimentally infected with H somnus. However, neither heat- nor formalin-killed, logarithmically growing neither H somnus nor in vitro passaged H somnus showed any effect on the phagocytic activity of these cells. In contrast to BAM, bovine blood monocytes (BBM), had a significant increase in their phagocytic activity following in vitro exposure to logarithmically growing H somnus. The bactericidal ability of bovine mononuclear phagocytes in interaction with H somnus was studied using two in vitro assay systems measuring nitric oxide (NO) production and chemiluminescence response. H somnus rapidly inhibited the Luminol- dependent chemiluminescence (LDCL) of BBM, and of BAM costimulated with opsonized Staphylococcus aureus. Inhibition of the LDCL response of BBM and BAM was abrogated with either opsonized or killed H somnus. In contrast to inhibition LDCL of BMP, both BBM and BAM infected with H somnus had stimulated production of NO. Using a calorimetric bactericidal assay, it was found that: (1) H somnus was able to survive within BBM in vitro and the kinetics of its survival were similar to that seen in BBM isolated from experimentally infected cattle; (2) treatment of BBM with varying concentrations of (Formula) and E. coli LPS had no effect on the survival of H somnus. Moreover, using ultrastructural studies, and 3H_ uracil incorporation into nucleic acids, it was possible to demonstrate the survival of H somnus in BMP. These results indicate that the ability of H somnus to modulate microbicidal activity of BMP would, in turn, assist the intracellular survival and immunopathogenesis of bovine haemophilosis.en-USVeterinary MedicineBacterial DiseasesArticle