ILC2 memory: Recollection of previous activation

Abstract

Immunological memory, traditionally thought to belong to T and B cells, has now been extended to innate lymphocytes, including NK cells and ILC2s, myeloid cells such as macrophages, also termed "trained immunity" and more recently to epithelial stem cells. In this review, we discuss the mechanisms underlying memory generation on ILC2s and speculate about their potential role in human allergic diseases, such as asthma. Moreover, we examine the relevance of the spontaneous ILC2 activation in the lung during the neonatal period in order to efficiently respond to stimuli later in life. These "training" of neonatal ILC2s may have an impact on the generation of memory ILC2s in the adulthood.

Dimensions of immunologic memory

“…Yet another organizing principle for the presentation of the articles in this volume is the preferred temporospatial context explored for immunological memories. An emphasis on anatomic niches such as primary and secondary lymphoid organs, non‐lymphoid tissues including tumors is accompanied by temporal considerations that range from details of T‐ and B‐cell memory generation and maintenance to evolution at large . Altogether, we agree with the conclusion proposed in the introductory review; that immunologic memory is best conceived of as a multi‐dimensional concept with physical correlates in far more components of the adaptive and innate immune system than previously appreciated.…”

“…This is perhaps best illustrated by the prominence of “memory inflation,” the numerical expansion of virus‐specific memory T cells in certain experimental and naturally occurring scenarios as emphasized by several contributors . At the same time, the very concept of “immunological memory” has undergone a substantial “inflation” (as it were) of its own, being now invoked for cell types other than T and B cells (innate lymphocytes, monocyte/macrophages) and species other than vertebrates (invertebrates, plants, archaea, and bacteria) . Another topic extensively discussed throughout this issue is the role of persisting antigen in shaping immunological memory in the context of chronic viral infections, cancer and the preservation of protective immunity .…”

The role of type 2 innate lymphoid cells in eosinophilic asthma

“…Martinez‐Gonzalez et al. propose that these iILC2 cells are not resident in the lung and rather migrate from the gut . Lastly, skin ILC2s have been shown to have high expression of ST2, whereas other studies show that skin ILC2 activation is TSLP mediated and independent of IL‐33 .…”

New insights into the function, development, and plasticity of type 2 innate lymphoid cells

“…Some evidence points towards the role of RAG‐1 in acquiring the memory features of NK cells another study demonstrated a transient expression of the RAG1 gene in mouse ILC2s during development . Preliminary data show that long‐term memory ILC2 responses are impaired in Rag 1 −/− mice, however, the absence of T and B lymphocytes may be relevant during the secondary challenge of memory‐like ILC2s . Other markers implicated in activation and memory functions in T cells are CD45RA and CD45RO.…”