Binding of bovine growth hormone to. Mycobacterium avium ss paratuberculosis

Mycobacterium avium ss paratuberculosis causes a chronic progressive enteritis in cattle and other ruminants referred to as Johne's disease. It also has been suggested by some as possibly being associated with Crohn's disease in humans. In a previous study we observed that incubation of bovine monocytes with recombinant bovine growth hormone (bGH) altered the ingestion and intracellular growth of M. avium ss paratuberculosis in vitro. This led us to investigate whether bGH also has a direct effect on M. avium ss paratuberculosis. We observed that addition of bGH (5 microg/ml) had a direct inhibitory effect on the growth of M. avium ss paratuberculosis in Middlebrook 7H9 broth. In contrast, the growth of Mycobacterium smegmatis was unaffected, even at a bGH concentration of 50 microg/ml. Using 125I-bGH we observed high affinity binding (Kd = 1.32 nM) of bGH to M. avium ss paratuberculosis, with an estimated 204 binding sites per bacillus. To the best of our knowledge, this is the first report of a mammalian hormone binding to this important enteric pathogen.

Hormonal modulation of phagocytosis and intracellular growth of Mycobacterium avium ss. paratuberculosis In bovine peripheral blood monocytes

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 of Mycobacterium avium ss. paratuberculosis within bovine peripheral blood monocytes. Phagocytosis of M. avium ss. paratuberculosis declined 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 Log10 greater number of M. avium ss. paratuberculosis in 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 when M. avium ss. paratuberculosis monocytes 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 of M. avium ss. paratuberculosis in bovine monocytes.