Functional characteristics of intraepithelial lymphocytes from mouse small intestine. III. Inability of intraepithelial lymphocytes to induce a systemic graft-versus-host reaction is because of failure to migrate in vivo.

Human intraepithelial lymphocytes

“…This concept is supported by many of their morphological features and is consistent with the presence of certain phenotypic markers of activation. Furthermore, the motile appearance of IEL in vivo and high locomotor activity in vitro [2], as well as their ability to accumulate in inflamed tissues (Table 4), is consistent with an activation level above the resting state. As IEL are not in mitosis and do not express activation markers such as IL 2 receptors and MHC class 1I molecules, they are clearly not true lymphoblasts.…”

“…6). Although the poor yield of isolated IEL has limited further studies of this type, mouse IEL have also been found to produce a local GvHR in the popliteal lymph node after transfer into the footpad of semiallogeneic hosts [2,19]. This local GvHR reflects non-specific activation and recruitment of host cells similar to that found in a DTH reaction, supporting the in vitro evidence that IEL are capable of secreting lymphokines.…”

“…Almost 75 % of IEL are CD8 § and many of these do not express certain pan T cell markers found on conventional T lymphocytes. IEL do not recirculate through lymphoid tissues in vivo [2], normally do not produce IL 2, and have little or no proliferative capacity in vitro. They can act as specific CTL, may mediate local DTH responses and can secrete certain lymphokines, including IL 3 and IFN-'y.…”

“…The ultimate fate of IEL after leaving the epithelium is entirely unknown. Despite initial evidence to the contrary [38], detailed studies in mice show that isolated IEL have no capacity to return to the mucosa by recirculating through blood and lymphoid tissues [2]. Therefore, it must be assumed that IEL either die in the LP or use less conventional routes of migration to re-enter lymphoid tissues.…”