CD4 and immunoglobulin G4-related sclerosing disease: Several studies have assessed the pathological T‐cell response in IgG4‐RD, with a focus on Th2 cells (Zen et al, 2007; Tanaka et al, 2012; Müller et al, 2013; Heeringa et al, 2018) and, more recently, CD4+ cytotoxic T lymphocytes (CD4+ CTL) (Mattoo et al, 2016; Maehara et al, 2017) and PD‐1hiCXCR5− peripheral T helper (Tph)‐like cells (Rao et al, 2017; Kamekura et al, 2018).