The mononuclear cell series in leprosy: an ultrastructural report

Abstract

Ultrastructural observations were carried out on the mononuclear phagocytic series, the host cells of Mycobacterium leprae, throughout the spectrum of leprosy [in humans]. The changes seen in these cells at various points in the immunological spectrum indicated differences ranging from the state of non-specific stimulation which occurs on the entry of M. leprae into the macrophage to the more specific activation which takes place in the presence of immune mechanisms. The most highly differentiated of the cell types was the epithelioid cell which appeared when hypersensitivity was maximal, in tuberculoid lesions and in positive Mitsuda skin tests. Cells described in the literature as A type epithelioid thought to be an immature epithelioid cell had much rough endoplasmic reticulum while B type epithelioid cells thought to be an end cell had numerous smooth lined vesicles. Lepromatous leprosy was characterized by a small undifferentiated immature bacteria-laden macrophage. An intermediate cell stage was seen in BB [mid-borderline] leprosy. The cells of BB leprosy were activated macrophages with high phagocytic potential. All gradations in the proportion of endoplasmic reticulum to vesicles of macrophages, from the activated cell seen in BB to A type epithelioid cells seen in low antigen, high resistance BT [borderline-tuberculoid] to mainly B type cells in downgrading BT were encountered. This supported the continuous spectrum of macrophage development seen throughout the spectrum of leprosy.