Evaluation of nitrite production and bactericidal activities of peripheral blood mononuclear cells following experimental inoculation with Salmonella Gallinarum
Nitric oxide (NO), a metabolite of activated macrophages has been shown as an important cytotoxic effector molecule, important in non-specific immunity, against pathogenic microbes. Therefore, the present study was conducted to evaluate nitrite production by peripheral blood mononuclear cells (PBMCs) from experimentally Salmonella Gallinarum inoculated birds and their intracellular killing capability for the intracellular avian pathogen, S. Gallinarum. Six to eight week old one hundred clinically healthy chicks, serologically negative for S. Gallinarum - Pullorum, were randomly divided into five groups with 20 birds each, including suitable control. Four groups were inoculated with live bacteria and sonicated antigen separately of the reference (E-76) and field (E-3019) strain of S. Gallinarum, respectively. Nitrite production ability of PBMCs studied at different time intervals viz. 24, 48, 72 and 96 hrs of in vitro stimulation with LPS, at 7 day post inoculation (DPI), showed optimal nitrite production at 24 hr for E-3019 and 48 to 72 hr for E-76 strain. Live bacteria inoculated birds showed a higher nitrite production than the sonicated antigen inoculated birds. Similar pattern, but with a comparatively lower production of nitrite by PBMCs, was observed at 30 DPI with both the groups. Bactericidal activity of PBMCs assessed at different intervals/conditions as for nitrite production assay, employing MTT dye, indicated that PBMCs of live bacteria inoculated groups showed more intracellular killing ability than sonicated antigen inoculated groups when in vitro stimulated with homologus sonicate antigen, at 7 DPI. Intracellular killing ability of PBMCs for field strain E-3019 exposed birds was maximum at 24 hrs, whereas for E-76 reference strain it was maximum at 48 hrs. Similar pattern of percent killing was observed at 30 days post inoculation but with slight lower trends in percent killing. Nitrite production abilities of the activated PBMCs showed a direct correlation with the intracellular killing of S. Gallinarum, suggesting nitrite to be an important bactericidal agent.
Fowl typhoid, Salmonella Gallinarum, nitrite production, bactericidal activity, Peripheral blood mononuclear cells.