Epidermal keratinocyte Ia expression, Langerhans cell hyperplasia and lymphocytic infiltration in skin lesions of leprosy.

Epidermal changes, Ia expression on keratinocytes, Langerhans cell hyperplasia and lymphocyte infiltration were sought in skin lesions of leprosy: 15 borderline tuberculoid (BT), six borderline lepromatous (BL), 17 lepromatous (LL), 13 erythema nodosum leprosum (ENL), six Lucio reactions and nine reversal reactions. All three changes were well developed in BT and reversal reactions. ENL showed well developed keratinocyte Ia and Langerhans cell hyperplasia, but little lymphocytic infiltration. LL and Lucio tissues had some Langerhans cell hyperplasia but little or no keratinocyte Ia or lymphocytic infiltration. BL tissues were so diverse as to suggest two distinct subgroups. These findings are consistent with the hypothesis that keratinocyte Ia expression is an immunohistological sign of a cell-mediated immune (CMI) response. However, the Ia keratinocyte expression found in BL and ENL tissues appears contrary to the undifferentiated macrophages and numerous bacilli found in the lesions. Thus, if a sign of CMI, keratinocyte Ia expression is not a measure of the effectiveness of the response.