Intramucosal Lymphocytes of the Gut: Lyt-2 and Thy-1 Phenotype of the Granulated Cells and Evidence for the Presence of Both T Cells and Mast Cell Precursors

The gut mucosa contains lymphocyte-like cells, a proportion of which contain a small number of granules that resemble those of mast cells in that they contain histamine and stain metachromatically. It has been suggested that these granulated lymphocytes represent transitional forms in the differentiation of T cells into mast cells. We used monoclonal antibodies and the fluorescence-activated cell sorter to analyze the expression of Thy-1 and Lyt-2 antigens on gut intramucosal lymphocytes with particular emphasis on the granulated cells. A minority of the granulated cells (10 to 20%) expressed Thy-1 antigen at high levels equivalent to those on cortical thymocytes. A much higher proportion of the granulated cells (about 90%) expressed readily detectable levels of Lyt-2 antigen and the most prevalent phenotype of the granulated lymphocytes (60 to 70%) was Lyt-2+, Thy-1-. Two operationally specific preparations of growth factors, one maintaining the proliferation of T cells and containing T cell growth factor, and the other containing a factor stimulating the growth of persisting (P) cells that are probably mast cell progenitors, were tested on lymphocytes from the gut mucosa. By using the appropriate preparation of growth factors, both T and P cells could be grown readily from the preparation of gut intramucosal lymphocytes. Estimates of the frequency of P cell precursors among these cells indicated a minimum of one in 300 could give rise to cells resembling mast cells. Fractions of Lyt-2+ cells that were enriched in granulated cells had few detectable P cell precursors, an observation lessening the likelihood that the granulated cells were progenitors of the P cells. The precise relationship of the granulated lymphocytes (mainly Lyt-2+, Thy-1-) to T cells remains to be established.