Neutrophils-typical atypical antigen presenting cells?

Neutrophils are the most abundant cells of the immune system and key in combating infections through phagocytosis, reactive oxygen species, neutrophil extracellular traps, and secretion of cytokines and antimicrobial peptides. Beyond this, they may influence the adaptive immune response by modulating CD4⁺ T cell responses. In response to cytokines, mainly GM-CSF, but also IFN-γ and TNF-α, neutrophils express major histocompatibility complex class II molecules on their surface. However, to function as antigen-presenting cells for CD4⁺ T cells, more requirements need to be fulfilled, like antigen internalization, processing into fragments containing T cell epitopes, and their presentation on the cell surface together with costimulatory molecules. Here, studies investigating the key features of antigen-presentation by neutrophils are summarized and discussed. Together, they provide evidence for a potential of neutrophils to specifically activate antigen-experienced CD4⁺ T cells.