Amplification of T-cell response to PPD by epidermal cell suspensions containing HLA-DR-expressing keratinocytes

The biological importance of the presence of class II transplantation antigens on highly differentiated epithelial cells such as keratinocytes in certain conditions, is still unknown. We have therefore investigated the antigen-presenting capacity of separated human epidermal cells obtained from tuberculin-reactive skin 6 days after intradermal injection of purified protein derivative (PPD). Earlier studies have shown a high percentage of HLA-DR-expressing keratinocytes at this time. Peripheral adherent blood cells were used as control stimulator cells and highly purified peripheral blood T lymphocytes as responder cells. The T-cell proliferation in response to PPD in the presence of autologous epidermal cells from normal and tuberculin-reactive skin was measured by [3H]thymidine incorporation on day 6. The latter cell population, 76-86% of which consisted of HLA-DR-expressing cells as judged by immunocytochemistry, induced a greater T-cell response to PPD than do normal epidermal cells. This discrepancy in the T-cell proliferation could not be explained by a difference in the numbers of anti-Leu 6 or anti-HLA-DQ-reactive Langerhans cells. The present data indicate that epidermal cell suspensions containing HLA-DR-expressing keratinocytes induce a greater T-cell response to PPD than do normal epidermal cells.