The immune response against Salmonella gallinarum infection was investigated in immunosuppresed chickens. Newly hatched chickens were treated with cyclophosphamide at the first and second day after birth and were challenged intraperitoneally with S gallinarum (1×10^7 CFU/㎖) on day 6. Group 1, Immunosuppresed and Challenged group, was treated with cyclophosphamide and challenged with S gallinarum; group 2, Immunosuppressed group, was only treated with cyclophsphamide; group 3, Challenged group, was only challenged with S gallinarum; group 4, Control group.
In each group, the localization of lymphocytes of the lymphoid organs and intestine was immunohistochemically compared using a variety of monoclonal antiboies (CD4^+, CD8^+, and B lymphocyte). Also, S gallinarum were assessed by Maccallum-Goodpasture stain and Immunohistochemical analysis in the paraffin-embedded intestinal tissues. In S gallinarum challenged chickens, CD4^+ and CD8^+ lymphocytes of the intestinal organs such as duodenum, jejunum, ileum and colon were increased. However, in cyclophophamide treated chickens, CD4^+ and CD8^+ lymphocytes and especially B lymbphcytes of the lymphoid organs such as thymus, spleen, and bursa of Fabricius were dramatically decreased.
These results suggest that cyclophsophamide is an immnosuppressive agent that especially causes depletion of B lymphocytes, suppress humoral immunity and eventually suppresses avian immune responses. Its protection against S gallinarum infection is mainly dependent on both cell-mediated mechanism and the humoral immune response.
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