TGFB1 and mature T-cell and NK-cell non-Hodgkin lymphoma: The Tfh‐like nature of AITL could be responsible for the elevation of IgA serum levels; Tfh cells produce TGF‐β1 and IL‐12, which bring about the induction and differentiation of IgA‐plasmablasts.26 A number of previous studies reported an association between AITL and IgA; in those studies, AITL was associated with atypical linear IgA dermatosis,37 IgA nephropathy,38 and leukocytoclastic vasculitis with IgA deposits.39 Kato et al reported that, in a series of Japanese patients with HTLV‐1‐negative nodal PTCL, elevated serum IgA levels were found in 47% of patients with AITL.