Immunological significance of changes in lymph nodes across the leprosy spectrum.

Seventy-seven lymph nodes were examined histologically from sixty-two leprosy patients representing the whole range of the disease spectrum from the high resistance form (tuberculoid) to the specific immunity deficiency form (lepromatous). At the lepromatous end of the spectrum paracortical areas were infiltrated with undifferentiated cells of the histiocyte–macrophage series which failed to eliminate mycobacteria. As resistance to infection increased across the leprosy spectrum, histiocytes became more differentiated eventually appearing epithelioid. This was paralleled by increasing numbers of small lymphocytes in the paracortical areas. In the borderline tuberculoid form of the disease an appearance was seen similar to that found in sarcoidosis. In polar tuberculoid leprosy where there is a high degree of cellular immunity, paracortical areas were well developed and populated with lymphocytes and immunoblasts. The immunological significance of these findings are discussed, especially the relation of the changes in morphological appearance of cells of the histiocyte series to the ability of the patient to develop cell-mediated immune reactions.