Lymphocyte-filled villi: comparison with other lymphoid aggregations in the mucosa of the human small intestine.

BACKGROUND & AIMS: Solitary lymphoid structures that may be sites of primary extrathymic T-cell differentiation have been described recently in murine (cryptopatches) and rat (lymphocyte-filled villi) small intestine. This study tests the hypothesis that similar structures occur in human small intestine.

METHODS

Normal small intestine was obtained during surgery. Fixed tissue was examined histologically, and frozen sections were examined by an indirect immunoperoxidase technique using a panel of mouse monoclonal antibodies.

RESULTS

A new isolated lymphoid structure, with epithelium resembling follicle-associated epithelium of Peyer's patches, is described as a lymphocyte-filled villus. These structures contain major histocompatibility complex (MHC) class II-positive dendritic cells, a majority of memory T cells, a variable B-cell component, and no evidence of immature lymphocytes that express either c-kit or CD1a. Two previously described lymphoid aggregations (isolated lymphoid follicles and submucosal lymphoid aggregations) are components of a single structure. The complete structure contains a B-cell follicle, T cells with mainly memory (CD45RO-positive) phenotype, high endothelial venules, and no detectable population of immature lymphocytes.

CONCLUSIONS

A new solitary lymphoid structure is described in the human small intestine. Neither these structures nor isolated lymphoid follicles appear to be similar to solitary primary lymphoid structures in rodent intestine.