Compared with T lymphocytes from other organs, intestinal intraepithelial lymphocytes (IEL) proliferate weakly in response to CD3/TCR ligation, and they do not respond at all to treatment with other mitogenic stimuli. These signals also failed to induce expression of the IL-2R α-chain on the surface of most IEL. IEL from germ-free mice, from Vγ1.1-transgenic mice, and from β2-microglobulin-deficient mice also gave a weak proliferative response. Therefore, the low proliferative response is not linked to the level of exposure to gut bacterial flora, the Vγ region expressed by the TCR-γδ+ IEL, or the presence of class I molecules that may be recognized by CD8+ IEL. The relatively small amount of proliferation in response to TCR signaling, therefore, is not likely to be the result of induction of anergy caused by previous contact with Ag. In contrast, ligation of the CD3/TCR complex could elicit a rapid cytotoxic response and serine esterase release by IEL. The unusual functional capabilities and the activation state of IEL are independent of the TCR isotype expressed by these cells. Freshly isolated IEL have a high intracellular microtubule-associated protein kinase-2 (MAP- 2K) activity level, further suggesting that these cells are activated despite their weak proliferative response. Consistent with this, MAP-2K is tyrosine- phosphorylated in both untreated and PMA-treated IEL. In contrast, MAP-2K activation and tyrosine phosphorylation occur in other T cells only when they are activated by PMA or other treatments. MAP-2K activity also is elevated in IEL from germ-free mice, demonstrating that activation does not depend on normal levels of exposure to bacterial flora. The activation of protein kinases such as MAP-2K could reflect the differentiation state of IEL or Ag receptor stimulation of some of these cells by epithelial cells in the preparation.
|Number of pages||13|
|Journal||Journal of Immunology|
|State||Published - Jan 1 1993|