Lichenoid tissue reaction induced by local transfer of Ia-reactive T-cell clones. III. Role of Ia+ keratinocytes in the epidermotropic migration of the T cells.

The role of Ia+ keratinocytes in epidermotropism of T cells was analyzed by using self-IA specific autoreactive cloned T cells with epidermotropic nature (termed BB5) and those without it (termed C10). These T-cell clones were injected into the footpads of syngeneic nude mice whose keratinocytes had been induced to express Ia by the iv injection of normal mouse serum. Ia expression by keratinocytes was associated with the increased epidermal invasion of BB5 cells, but did not render C10 cells capable of migrating into the epidermis. The migration of the T cells to epidermis was also studied in vitro using a migration assay under agar. Ia expression by keratinocytes significantly enhanced the in vitro migration of BB5 cells to the epidermis, but had no effect on the migration of C10 cells and freshly isolated unstimulated lymphocytes. We surmise from these results that Ia+ keratinocytes may facilitate the epidermal invasion of the T cells with epidermotropic nature, but not those without it. However, the possibility certainly exists that the observed preferential migration of BB5 cells to Ia+ keratinocytes may be secondary to the alteration of other factors associated with the Ia expression. The injection of normal mouse serum was accompanied by an increase in the production of epidermal cell-derived thymocyte activating factor (ETAF) indicating that the increased ETAF production may have contributed to some of the observed preferential migration of BB5 cells.