Effect ofHaemophilus somnuson nitric oxide production and chemiluminescence response of bovine blood monocytes and alveolar macrophages

Abstract

Haemophilus somnusis able to survive and multiply in bovine blood monocytes (BBM) and alveolar macrophages (BAM), but the mechanisms used byH. somnusto evade killing mechanisms of bovine mononuclear phagocytes are not completely understood. To study the bactericidal ability of bovine mononuclear phagocytes following interaction withH. somnus,in vitroassay systems were developed to detect the luminol-dependent chemiluminescence response (LDCL) and nitric oxide (NO) production of BBM and BAM. Live logarithmically growing or stationary phaseH. somnusinhibited the LDCL of BBM and BAM costimulated with opsonizedStaphylococcus aureus. Inhibition of the LDCL response of BBM and BAM was not mediated by liveH. somnusopsonized with hyperimmune serum, or by killed bacteria.H. somnusstimulated both BBM and BAM to produce NO at levels comparable withEscherichia colilipopolysaccharide. While NO was being produced, viableH. somnuscould still be isolated from the cell cultures. The ability ofH. somnusto inhibit LDCL of both BBM and BAM, and resistance to NO killing may be an important mechanism that contributes to survival of the organism following ingestion by bovine mononuclear phagocytes.