T-CELL SUBSETS AND LANGERHANS CELLS IN THE FORESTOMACH MUCOSA OF ADULT SHEEP AND SHEEP FETUSES

.As part of a study on leukocytes in the ruminant forestomach the occu rrence and distribution of T cells and major histocompatibility comple x Class II positive (MHC-II +) cells in the forestomach mucosa of shee p were investigated. Samples were taken from the reticulum, atrium rum inis, ventral rumen, dorsal rumen and omasum of five healthy adult ewe s and seven nearly fullborne foetuses. Frozen sections were stained wi th an indirect immunoperoxidase method using monoclonal antibodies aga inst sheep MHC-II, CD4 and CD8 molecules and the sheep gamma delta T c ell receptor, Both MHC-II+ cells and T cells were distributed along th e basal lamina of the epithelium, with either mainly intraepithelial ( CD8 + and gamma delta + cells) or mainly subepithelial (MHC-II + and C D4 + cells) location. The MHC-II + cells showed dendritic morphology a nd were interpreted as Langerhans cells. In adult ewes CD4 + T cells c omprised the major T cell subset at all sample sites. The number of T cells declined from the atrium ruminis through the ventral rumen to th e dorsal rumen, while the number of Langerhans cells showed no marked variation between different sample sites. In foetuses, Langerhans cell s showed a relatively high prevalence, while T cells were sparse and s howed a more random distribution in the rumen wall. No marked variatio n between sample sites were observed in the fetal forestomachs. It is concluded that Langerhans cells and T cells are normally present in th e forestomach mucosa of sheep, and it is suggested that the Langerhans cells represent a constituent component, while the prevalence and dis tribution of T cells may be influenced by antigen leakage through the epithelium.