Gamma/delta T cell response of chickens after oral administration of attenuated and non-attenuated Salmonellatyphimurium strains

Abstract

Poultry represents an important source of Salmonella infection in man. Despite intensive research on immunity, little is known about the involvement of T cell sub-populations in the immunological response of chickens against infection with non-host-adapted Salmonella ( S.) serovars. In this study, the T cell composition of blood lymphocytes (CD4 +CD8 +; CD4 +CD8 −; CD4 −CD8 +; CD8 +TcR1 +; CD8 −TcR1 +, CD8 +TcR1 −) after oral administration of the non-attenuated S. typhimurium wild-type strain 421 (infection) or the attenuated vaccine strain Salmonella vac ® T (immunization) to day-old chicks was investigated and compared with non-treated chickens by flow cytofluorometry. Additionally, the occurrence of T cell sub-populations (CD4 +; CD8 +; TcR1 +(γδ); TcR2 +(αβ 1)) in ceca, spleen and bursa of Fabricius of the birds was studied immunohistologically. Blood samples and tissues were examined between days 1 and 12 of age. Chicks inoculated with S. typhimurium 421 or Salmonella vac ® T showed significantly elevated percentages of CD8 +TcR1 + in blood on days 7, 8 and 9, or on day 8 in comparison to control animals. The CD4 to CD8 cell ratio was about 3:1 in infected animals on day 5 of age. In the organs of treated chicks the numbers of CD8 +(γδ) and TcR1 +(γδ) cells had markedly increased on days 4 and 5 in ceca, 8 and 9 in the bursa and 9 and 12 in the spleen. Moreover, infected or vaccinated birds revealed larger quantities of CD4 + and TcR2 + T cells in ceca on days 4 and 5. As shown by double staining, the TcR1 + cells in the organs of infected animals additionally carried the CD8 antigen. In conclusion, immunization of day-old chicks with the attenuated Salmonella live vaccine strain resulted in the same changes in T cell composition as seen after infection with the non-attenuated Salmonella wild-type strain, but at a lower level. The remarkable increase of CD8 +TcR1 +(γδ) double positive cells in treated birds indicates an important role of this cell sub-population in the immunological defense of chickens against Salmonella exposure.