CD4+CD8+ and CD8α+β- T lymphocytes in human small intestinal lamina propria

Objective To examine CD8 expression by T-lymphocyte subpopulations from disease-free human lamina propria. Methods Single-cell suspensions were prepared from the epithelial layer and the lamina propria of small intestinal biopsies obtained endoscopically from disease-free patients. Monoclonal antibodies against CD3, CD4, CD8, CD56, CD8 alpha beta, CD8 alpha, TCR alpha beta and TCR gamma delta were used for dual and three-colour flow cytometric analysis. Results In addition to classical CD4(+) and CD8(+) T lymphocytes a substantial proportion of lamina propria T lymphocytes were CD4(+)CD8(+) or 'double positive' (mean 14% range 4-26%), This population was significantly lower in the epithelial layer of the same patients (mean 7%, range 3-21%, P < 0.007). Three-colour flow cytometric analysis revealed that expression of the CD8 molecule on double positive T cells in the lamina propria was limited to the CD8 alpha chain. Furthermore, of the CD8(+) population, CD8(+) T cells which only expressed the alpha chain were present in greater numbers in the lamina propria (mean 35%, range 14-54%) than in the epithelial layer (mean 18%, range 5-37%, P < 0.02). NK (CD56(+)) cells were not detected and few gamma delta TCR+ T lymphocytes were detected in the lamina propria (mean 2%, range 0.5-6.6%) when compared with the epithelial layer (mean 8%, range 0.2-14%, P< 0.008). Conclusion A significant population of CD4(+)CD8 alpha(+) T lymphocytes which are CD8 beta chain negative have been detected in the intestinal lamina propria. These cells form a more significant component of the lamina propria than the epithelial layer T-cell repertoire and may have a unique function in intestinal immunoregulation. (C) 1998 Lippincott-Raven Publishers.