Demonstration of mycobacterial antigens in skin biopsies fron suspected leprosy cases in the absence of bacilli.

Skin-biopsies from fifty-six patients suspected of early leprosy from Bahia State, Brazil, were examined histopathologically. The Fite-Faraco staining failed to demonstrate acid-fast bacilli in this material. The prominent features of the lesions were inflammation of the neurovascular bundles and sometimes inflammation of the skin appendages. The non-specific infiltrate was predominantly composed of histiocytes and lymphocytes. In 41 cases (73.2%) epidermal atrophy was also present. The avidin-biotin peroxidase technique was used with primary antibodies to detect bacillary antigens (anti-BCG serum) and nerve branches (anti-S-100 protein serum). Immunohistochemical detection of bacillary antigens using the anti-BCG serum was positive in 28 cases (50%). A positive staining for S-100 protein was observed in 40 cases (71.4%) in dendritic antigen-presenting cells of the skin. The detection of bacillary antigens, together with the clear demonstration of nerve bundles enhanced our capacity to fulfill morphologic criteria for the diagnosis of early leprosy. Our observations indicate that the use of immunohistochemical methods represent a useful tool for the early diagnosis of leprosy.