Pathogenic memory type Th2 cells in allergic inflammation

•IL-5 producing memory Th populations are crucial for pathogenesis of Th diseases.•Pathogenic memory Th2 cells play critical roles in eosinophilic inflammation in lung and skin.•Pathogenic memory Th2 cells and ILC2 share several characteristic features.•Il5 is uniquely regulated by the transcription factor Eomes in memory Th2 cells.

Immunological memory is a hallmark of adaptive immunity. Memory CD4 T helper (Th) cells are central to acquired immunity, and vaccines for infectious diseases are developed based on this concept. However, memory Th cells also play a critical role in the pathogenesis of various chronic inflammatory diseases, including asthma. We refer to these populations as ‘pathogenic memory Th cells.’ Here, we review recent developments highlighting the functions and characteristics of several pathogenic memory type Th2 cell subsets in allergic inflammation. Also discussed are the similarities and differences between pathogenic memory Th2 cells and recently identified type 2 innate lymphoid cells (ILC2), focusing on cytokine production and phenotypic profiles.