Leprosy is teaching us the immunopathogenesis of inflammatory skin disease

The TH22 subset has been discovered in leprosy, with increased IL-22 in TH2 anergic lepromatous leprosy and decreased IL-22 in TH1 tuberculoid leprosy with intact cell-mediated immunity.2 The increase in IL-22 at the TH2 lepromatous pole corresponds to the increase in IL-22 in TH2 atopic dermatitis versus TH1 psoriasis.1 TH22 is well established in both TH1 psoriasis and TH2 atopic dermatitis.3 Leprosy is the first disease classified by the T cell, with TH1 paucibacillary tuberculoid disease with intact cell-mediated immunity and TH2 multibacillary lepromatous disease anergic to Mycobacterium leprae epitopes.4 TH22 cells like TH17 cells are less stable phenotypes compared with the polar TH1 and TH2 subsets.