Analysis of the Effector Functions of Different Populations of Mucosal Lymphocytes*

Abstract

Lymphocytes separated from the epithelial layer of mouse small intestine, IEL, were tested for their NK cytotoxicity against Yac-1 targets. There was little NK activity in a 4 hour assay, but high activity in an 18 hour assay, and the NK activity of IEL did not parallel that in the spleen in any of the mouse strains tested. Furthermore, IEL exerted a suppressor activity on mouse spleen NK activity. Specific T-cell cytotoxicity appeared in IEL in mice immunized with an intraperitoneal injection of P-815 tumor cells. By contrast with IEL, LPL had little NK or NK suppressor activity, but higher levels of specific T-cell cytotoxicity in tumor-immunized mice than intraepithelial lymphocytes. A high proportion of IEL had granules that stained with Giemsa and Astra blue. Furthermore many IEL carried Lyt-2+ phenotype and no other T-cell surface antigen. Intraepithelial lymphocytes appeared, therefore, to have staining and phenotype characteristics of both granular NK cells and suppressor cells. It was clear that the intestinal mucosa contained populations of immune effector cells that were heterogeneous in nature and function.

Ontogeny of the Thy-1-, Lyt-2+ murine intestinal intraepithelial lymphocyte. Characterization of a unique population of thymus-independent cytotoxic effector cells in the intestinal mucosa.

“…First, it is generally accepted that IEL are essentially void of B cells; <5% of the IEL bear surface Ig (J. R. Klein, unpublished observation, and ref. 14). Consistent with that fact are the observations in the present study that nearly all IEL were either Lyt-2 + (80-90%) or L3T4 + (6-8%) cells, and as such, J1 ld must be expressed on one or both of those IEL subsets.…”

Intraepithelial lymphocytes. Anatomical site, not T cell receptor form, dictates phenotype and function.

“…In any case a mechanism for IEL precursors or their progeny to specifically home to the intestinal mucosa must exist. More precisely, IEL would require a mechanism for trafficking to the intestinal epithelium since other mucosal T cell populations such as lamina propria and Peyer's patch lymphocytes are not phenotypically similar to IEL (40). It is interesting to note that IEL do not express the MEL-14 lymphocyte homing receptor (23).…”

Distinct cell types control lymphoid subset development by means of IL-15 and IL-15 receptor α expression

“…TCR␣␤ IEL can also be subdivided based on CD8␣, CD8␤, and Thy1 expression (23), and CD8␣␣TCR␣␤ IEL require IL-15͞IL-15R␣ for development (3,4). In the IL-15R␣ Ϫ/Ϫ chimeras, analysis of IEL revealed little differences in the development of the overall CD8␣TCR␣␤ population (Fig.…”

“…TCR␥␦ IEL can be furthered subdivided into Thy1 ϩ and Thy1 Ϫ populations (23). Thy1 expression by IEL is thought to be a marker of TCR-triggered activation (24).…”