Cellular and humoral immune responses in calves experimentally infected with Salmonella dublin.

Both humoral and cellular immune responses have been found to be operative in calves surviving smooth Salmonella dublin infection. Such calves showed rises in agglutinin titre and serum immunoglobulin as compared to uninfected controls. These calves at 3 weeks post infection showed a 3-4 fold increase of initial skin thickness at 5 h post antigen inoculation - an indication of immediate type of skin hypersensitivity reaction. The maximum increase in skin thickness of 2-3 fold was observed at 48 h post antigen inoculation - a criterion of delayed type of hypersensitivity reaction. There was a moderate increase, 28.1 per cent in the migration inhibition of peripheral leucocytes during the first week and a sharp increase, 45.7 and 66.6 per cent during the second and third week post infection, respectively. Passively immunized calves on challenge exhibited delayed clinical symptoms and mortality as compared to control animals, though the calves could not be protected against challenge. The serum immunoglobulin levels in passively immunized calves decreased moderately during the first week and markedly during the second week post challenge while in the control calves the levels dropped abruptly in the first week followed by death in both groups.