Nucleated Fish Erythrocyte Extracellular Traps (FEETs) release is an evolutionary conserved immune defence process

Fish erythrocytes remain nucleated for their life-span, unlike mammalian erythrocytes which undergo enucleation. Asides transportation of oxygen, fish erythrocytes are capable of several immune defence processes. Nucleated fish erythrocytes represent prime candidates for carrying out ETotic responses. ETosis is an evolutionary conserved innate immune defence process found in both vertebrates and invertebrates, which involves the extrusion of DNA studded with antimicrobial proteins into the extracellular space serving to trap and kill microorganisms. In this report, we demonstrate that fish erythrocytes isolated from Danio rerio (zebrafish) produce ETotic-like responses when exposed to chemical and physiological stimuli. Salmo salar (Atlantic salmon) erythrocytes produce similar ETotic responses. We have termed these ET-like formations Fish Erythrocyte Extracellular Traps (FEETs). Interestingly, we discovered that mammalian inducers of NETosis, such as the protein kinase C (PKC) activator phorbol 12‐myristate 13‐acetate and the calcium ionophore ionomycin induced FEETs. Moreover, we found that FEETs are dependent upon activation of PKC and generation of mitochondrial reactive oxygen species. Thus, this brief report represents the first demonstration that fish erythrocytes can exhibit ETotic-like responses, unveiling a previously unknown function of nucleated erythrocytes, and sheds new light on the innate immune arsenal of erythrocytes.

A novel role for the transcription factor HIF-1α in the formation of mast cell extracellular traps

MCs (mast cells) are critical components of the host innate immune defence against bacterial pathogens, providing a variety of intra- and extra-cellular antimicrobial functions. In the present study we show, for the first time, that the transcriptional regulator HIF-1α (hypoxia-inducible factor-1α) mediates the extracellular antimicrobial activity of human and murine MCs by increasing the formation of MCETs (MC extracellular traps).