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 ho rmone, prolactin, vitamin D-3, luteinizing hormone, oxytocin) on the phagoc ytosis and intracellular survival of Mycobacterium avium ss. paratuberculos is within bovine peripheral blood monocytes. Phagocytosis of M. avium ss. p aratuberculosis declined in a dose-dependent manner when monocytes were exp osed to increasing amounts of recombinant bovine growth hormone, with littl e phagocytosis occurring at a growth hormone concentration of 50 ng/ml. The other hormones tested had little effect on phagocytosis. Continuous exposu re of bovine monocytes to bovine growth hormone (10ng per ml) resulted in e nhanced intracellular bacillary growth. This was detected within 3 days of monocyte infection, and resulted in a 1 Log(10) 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 mul tiplication 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 c an affect the intracellular multiplication of M. avium ss. paratuberculosis in bovine monocytes. (C) 1999 Academic Press.