Cellular Innate Immunity: An Old Game with New Players

Abstract

Innate immunity is a rapidly evolving field with novel cell types and molecular pathways being discovered and paradigms changing continuously. Innate and adaptive immune responses are traditionally viewed as separate from each other, but emerging evidence suggests that they overlap and mutually interact. Recently discovered cell types, particularly innate lymphoid cells and myeloid-derived suppressor cells, are gaining increasing attention. Here, we summarize and highlight current concepts in the field, focusing on innate immune cells as well as the inflammasome and DNA sensing which appear to be critical for the activation and orchestration of innate immunity, and may provide novel therapeutic opportunities for treating autoimmune, autoinflammatory, and infectious diseases.

Fig. 1

Key immune effector cells (phagocytes and lymphocytes) and regulatory cells (T regulatory cells, Tregs; myeloid-derived suppressor cells, MDSCs). Macrophages show different phenotypes, with M1 and M2 being the main subtypes. Beyond this plasticity, macrophages are the main cells responsible for inflammasome activity (leading to proinflammatory IL-1β and IL-18 production). Specific to neutrophils is the release of their own DNA, called neutrophil extracellular traps (NETs), which can entrap and immobilize pathogens. In addition to traditional adaptive T and B cell subsets, lymphocytes also encompass the innate lymphoid cells (ILCs) that belong to the innate immune system. In analogy to Th1/Th2, ILCs comprise at least 3 different subtypes, termed ILC1, ILC2, and ILC3.