CD28 and hypereosinophilic syndrome: Interestingly, the CD4+ Th2 cells found in a condition related to IgG4-RD and called “lymphocytic variant of human hypereosinophilic syndrome” are reminiscent of activated LatY136F CD4+ T cells in that they express low levels of TCR at their surface and primarily respond to CD28 signals (Carpentier et al., 2020; Roufosse et al., 1999).