Abstract
In this chapter, we will explain that the innate immune system has effector functions that allow a very early response to invading pathogens as well as to non-microbial danger signals. We will discuss the properties and functions of myeloid cells of innate immunity, such as monocytes, DCs, macrophages and neutrophils. The latter two cell types perform phagocytosis, i.e., a process of ingesting extracellular substrates, such as microbes, followed by intracellular destruction. The recognition of PAMPs via PRRs starts a signal transduction cascade that involves the activation of the inflammasome and the secretion of cytokines, such as IL1β. Epigenetic regulation is fundamental for the differentiation of immune cells, as well as for their adaptive response to several environmental challenges, such as microbe infections. These epigenetic processes are also the basis for trained immunity representing memory function of the innate immune system. Also, non-microbial damage-associated molecular patterns (DAMPs) can induce comparable inflammatory responses. Inflammation is mostly local but can also be systemically and depending on cytokine levels it may be protective or pathologic, such as in sepsis.