Pathogenesis of Leprosy: An Insight Into B Lymphocytes and Plasma Cells

The pathogenesis of leprosy is still not fully understood. Several studies have been performed on the involvement of T cells in leprosy and more recently have focused on genetic factors and innate immune response. There are still only few reports about the role of B cells in active leprosy lesions in different spectral forms of the disease. The literature on tuberculosis suggests that B cells play an important role in the regulation of the granulomas, in cytokine production, T-cell response, and antigen presentation. Only few studies investigated the role of B cell in leprosy. We investigated the distribution of B cells in 85 leprosy biopsies covering all forms of the disease and compared results with 13 biopsies of tuberculosis and atypical mycobacteriosis, expanding the previous experiences. A statistically significant difference in the number of CD20(+) (P = 0.014) and CD138(+) (P = 0.01) cells between the different forms of leprosy was observed. A remarkable amount of CD138(+) cells could also be detected in borderline tuberculoid. The median of the CD20(+) cells decreased from the bacilloscopy-negative samples to the bacilloscopy-positive samples by 50% (P = 0.004). Contrarily, the median of CD138(+) cells showed an increase from bacilloscopy-negative to bacilloscopy-positive samples of 966.67% (P = 0.001). In our experience, tuberculoid leprosy showed more B cells and less plasma cells than lepromatous leprosy. Our results show that B cells might be implicated in leprosy pathogenesis, not only in the lepromatous pole as previously postulated, but also in tuberculoid granuloma formation and type 1 reactions.