Phenotype of intraepithelial lymphocytes in euthymic and athymic mice: Implications for differentiation of cells bearing a CD3‐associated γδ T cell receptor

This study was carried out to determine the exact phenotype of intraepithelial lymphocytes (IEL) in euthymic and athymic nude mice. The phenotype of IEL in euthymic and athymic mice is mainly CD3+CD8+. However, based on Thy-1-and CD3-associated receptor expression we can subdivide the CD3CD8 population into different subpopulations in euthymic and athymic mice. In euthymic and athymic mice several CD3CD8 populations can be defined. One population expressing Thy-1 and the T cell receptor (TcR) αβ is absent in athymic mice. Two other CD3+CD8+ populations can be detected in euthymic and athymic mice. Based on Northern blot and flow cytometric analysis we have to conclude that these populations express the CD3-associated TcR γδ. One of the TcR γδ-expressing populations also expresses Thy-1 at low surface density. This is in contrast to the CD3CD8 population expressing the TcR αβ, which expresses Thy-1 at high surface density. There are also, however, especially in athymic nude mice, significant numbers of CD3−CD8+ cells present with the same localization as IEL. The function of these cells is yet unknown. Using a probe for the δ chain we have shown that IEL preferentially express 2-kb mRNA, while nearly no δ chain 1.7-kb mRNA is expressed by these cells. This is in contrast to δ mRNA in thymocytes. Equal quantities of the 1.7- and 2.0-kb δ chain mRNA species were found in RNA isolated from thymocytes. The results imply that CD3+CD8+ intestinal IEL expressing the CD3-associated TcR γδ can differentiate in absence of the thymus and represent a thymusindependent lineage of cells bearing this receptor.