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, CD8αβ, CD8α, TCRαβ and TCR-γδ 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 CD8α chain. Furthermore, of the CD8+ population, CD8+ T cells which only expressed the a 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 γδTCR+ 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+CD8α+ T lymphocytes which are CD8β 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.