High frequency of CD8 alpha alpha homodimer-bearing T cells in human fetal intestine.

Immunohistochemistry on frozen sections was used to identify CD8 alpha alpha cells and CD8 alpha beta cells in human intestine. As observed previously, CD8 alpha beta cells predominate (> 95%) in tonsil and post-natal intestine. However in human fetal intestine (16-24 weeks gestation), almost half the CD8+ cells in the lamina propria are CD8 alpha alpha, and many CD8 alpha alpha cells can be identified in the epithelium. In contrast, in the T cell zones of the Peyer's patches, CD8 alpha beta cells are dominant. The CD8 alpha alpha cells are virtually all alpha beta T cell receptor positive. By analogy with the murine system, these CD8 alpha alpha cells in the fetal gut may be directly derived from the marrow, undergoing thymus-independent differentiation in the gut mucosa.