The humoral and cell mediated immune response of young chicks to Salmonella typhimurium and S. Kedougou.

Day old chicks were inoculated with either Salmonella typhimurium or S. Kedougou as representative examples of an invasive and a non-invasive strain respectively. The titres of IgA, IgG and IgM antibodies were determined, using an enzyme-linked immunosorbent assay (ELISA) in the bile, serum and homogenates of intestinal mucosa each week up to 5 weeks of age. Statistically significant increases in antibodies were detected in the bile (IgA and IgG) and the intestinal mucosa and serum (IgG and IgM) 1 week after the birds were inoculated with S. typhimurium. In contrast, only a limited response was recorded for S. kedougou 4 weeks after challenge commenced. The birds appeared capable of eliminating systemic infection with S. typhimurium as they grew older although a cell mediated immune response was demonstrated in less than half the birds aged 4 or 5 weeks. The demonstration of only a limited serological response to S. kedougou indicates that serological testing may have a limited role in monitoring flocks for infection with non-invasive serotypes.