Increased Langerhans cell accumulation after mycobacterial stimuli

Abstract

Aims: To evaluate the role of Langerhans cells (LCs) in the local activation of leprosy lesions. LCs, acting as tolerance inducers and immune stimuli, are dendritic cells recently implicated in cutaneous homeostasis. The role of LCs in the defence against mycobacterial infection remains poorly understood.

Methods and results: The number and distribution of CD1a+ skin cells and HLA-DR and intercellular adhesion molecule (ICAM)-1 expression were analysed in leprosy skin lesions and in delayed-type hypersensitivity (DTH) tests. The results showed a high number of LCs in tuberculin and lepromin tests, in tuberculoid lesions and in the epidermis and dermis during type I and II reactions. In multibacillary lesions, however, the number of LCs was consistently low in comparison with other groups. Increased numbers of LCs were accompanied by marked HLA-DR and ICAM-1 expression, suggesting a strong relationship between these immunological events.

Conclusions: CD1a+ cells are implicated in the local immunological events taking place after mycobacterial stimuli and may account for the local activation of all types of reactional episodes in leprosy.

Figure 1

CD1 expression in leprosy skin lesions. A, a few positive cells in suprabasal localization of flattened epidermis of lepromatous leprosy/borderline leprosy patients. B, dendritic cells in upper layers of the thickened epidermis in a type II reaction patient. C, marked positive dendritic cells in a type I reaction patient. D, numerous positive cells in the dermis of a type II reaction patient. The original magnification is shown.

Figure 2

Quantification of CD1 expression in leprosy lesions in all groups studied [biopsy specimens of type I and type II reactions; tuberculoid (BT) and lepromatous (BL); and lepromin and purified protein derivative-positive tests (DTH)]. A, number of CD1+ epidermal cells per field. B, total number of CD+ dermal cells. Median ± 95% CI. A, *P < 0.05; **P < 0.0005; ***P < 0.005; ****P < 0.0001. B, *P < 0.05; **P < 0.005.

Figure 3

HLA-DR and intercellular adhesion molecule (ICAM)-1 expression in leprosy skin lesions. Figures are representative of HLA-DR (A–C) and ICAM-1 (D–F). A, only the dermal infiltrates are labelled in a type II reaction biopsy. B, fifty per cent of keratinocytes are labelled in a borderline tuberculoid patient. C, marked expression in type I reaction. D, labelled cells along the basal layer (type II reaction). E, two marked foci in type II reaction. F, the basal layer and addictional foci are stained in a delayed-type hypersensitivity group biopsy specimen. The original magnification is shown.

Figure 4

Relative density of keratinocytes expressing HLA-DR in leprosy lesions in all groups studied [biopsy specimens of type I and type II reactions; tuberculoid (BT) and lepromatous (BL)]. Semiquantitative score: absence of stained keratinocyte: (1) 25% of keratinocytes are HLA-DR+; (2) 50–75% of keratinocytes are HLA-DR+; (3) >75% of keratinocytes are HLA-DR+; (4) median ± 95% CI. *P < 0.001; **P < 0.0001; ***P < 0.05.