Differential expression of Langerhans cells in the epidermis of patients with leprosy

Eighteen patients with lepromatous leprosy (LL) showed a significant reduction (P less than 0.001) of Langerhans cells (LC) irrespective of whether the biopsies were obtained from involved (398 +/- 186) or healthy skin (304 +/- 98). The cells showed morphological changes consisting mainly of loss of dendritic processes. Twenty-four controls (age, sex and race matched) had a mean number of LC of 632 +/- 138. In tuberculoid patients (TT) significant differences were observed, depending on the site of biopsy. Nine biopsies from involved skin had 993 +/- 206 LC, whereas 11 from healthy skin had 448 +/- 96 (P less than 0.001). This difference was confirmed in six additional borderline tuberculoid (BT) and TT patients in whom biopsies were simultaneously obtained from involved (973 +/- 179) and uninvolved skin (498 +/- 99). In 10 patients with indeterminate leprosy the LC density did not differ from the control population (630 +/- 261). The expression of LC numbers in BT and TT patients may represent migration of these cells from healthy skin to involved areas or mobilization of a central pool. The low density found in LL patients could interfere with adequate presentation of mycobacterial antigens leading to tolerance. Alternatively the presence of T helper cells in TT infiltrates may produce factors that recruit LC; their absence in LL lesions may account for the decrease in LC expression.