Abstract
In this study, we evaluated the effects of several hormones (i.e. growth hormone, prolactin, vitamin D3, luteinizing hormone, oxytocin) on the phagocytosis and intracellular survival ofMycobacterium aviumss.paratuberculosiswithin bovine peripheral blood monocytes. Phagocytosis ofM. aviumss.paratuberculosisdeclined in a dose-dependent manner when monocytes were exposed to increasing amounts of recombinant bovine growth hormone, with little phagocytosis occurring at a growth hormone concentration of 50 ng/ml. The other hormones tested had little effect on phagocytosis. Continuous exposure of bovine monocytes to bovine growth hormone (10 ng per ml) resulted in enhanced intracellular bacillary growth. This was detected within 3 days of monocyte infection, and resulted in a 1 Log10greater number ofM. aviumss.paratuberculosisin growth hormone treated, than control, monocytes at 12 days of infection. When monocytes were incubated with growth hormone for only the first 5 days of a 12 day incubation period, a further increase in bacillary multiplication was observed. A similar increase in bacillary multiplication was observed whenM. aviumss.paratuberculosismonocytes were incubated with prolactin for the first 5 days of a 12 day incubation period. These data indicate that varying levels of growth hormone and prolactin can affect the intracellular multiplication ofM. aviumss.paratuberculosisin bovine monocytes.
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