Novel regulation of ILC by memory CD4 T cells during protective responses against influenza A virus

Abstract

Abstract The primary goal of vaccination is to protect individuals from the morbidity and mortality of pathogen exposure by generating immunological memory. Our current understanding is that memory CD4 T cells, commonly regarded as the regulators of memory cytotoxic CD8 T cells and/or antibody-producing B cells, provide protection by hastening pathogen clearance through ‘faster, bigger, and better’ immune responses. It is now clear, however, that many different subsets of CD4 T cells, many with specialized functions other than providing ‘help’, are generated during immune responses against pathogens. In studies designed to ascertain the full functional potential of memory CD4 T cells responding against influenza A virus (IAV), we found that virus induced TH1-like, as well as in vitro polarized TH1 or TH17 memory CD4 T cells, enhance early innate inflammatory responses that correlate with better and earlier control of IAV in infected lungs. In further studies, we found innate lymphoid cells (ILC), which are not normally associated with anti-viral responses but rather associated with healing and wound repair, are also mobilized by memory CD4 T cells during the early stage of the response against IAV. Unexpectedly, the protection afforded by memory CD4 T cells against lethal IAV challenge is significantly compromised when ILCs are depleted. These findings reveal a previously unappreciated beneficial role of memory CD4 T cells in regulating tissue homeostasis during recall responses against pathogens through the regulation of ILC subsets.