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

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 (R) 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(+)(gamma delta); TcR2(+)(alpha beta (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 (R) 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(+)(gamma delta) and TcR1(+)(gamma delta) 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(+)(gamma delta) double positive cells in treated birds indicates an important role of this cell sub-population in the immunological defense of chickens against Salmonella exposure. (C) 2001 Elsevier Science B.V. All rights reserved.