Reversal reaction in borderline leprosy is associated with a polarized shift to type 1-like Mycobacterium leprae T cell reactivity in lesional skin: a follow-up study.

Borderline leprosy patients often undergo acute changes in immune reactivity that manifest as reversal reaction (RR) in the course of the disease. RR is associated with an exacerbated local delayed-type cellular immune response to Mycobacterium leprae and is responsible for severe tissue damage. We investigated whether RR episodes are associated with a change in T cell subsets in the lesional skin with regard to their cytokine secretion profiles. M. leprae-responsive T cell lines and thereafter T cell clones (TCC) were generated from the lesional skin of seven untreated borderline leprosy patients (with or without RR) and again from three of these patients experiencing RR during treatment. The phenotypes of the M. leprae-responsive TCC were either CD4+, CD8+, CD4-/CD8+/TCR gammadelta+, or CD4-/CD8-/TCR gammadelta+, although most of them were CD4+. Regardless of the clinical status of the untreated patients, a major subset of the M. leprae-responsive TCC was type 0-like and produced both IFN-gamma and IL-4. Interestingly, in all three patients who experienced a (re)occurrence of RR during treatment after the first analysis, a clear shift to polarized IFN-gamma production by the M. leprae-responsive TCC (type 1-like) was observed. This shift in T cell subsets was also reflected in the observed decrease in serum IgG and IgM levels of the same patients during RR. These finding indicate that CD4+ M. leprae-responsive T cells with a polarized type 1-like phenotype might be responsible for the immune-mediated tissue damage occurring during RR.