Clotting the Gap Between Mitochondria-Mediated Immunity and Mitochondrial Transfer

Mitochondria are organelles that orchestrate numerous cell functions in addition to providing energy. During viral infection or in case of defects in mitochondrial replication, an intricate mechanism of self-destruction is engaged through the formation of mitochondrial pores. This leads to the release of mitochondrial DNA into the cytoplasm, where it triggers innate immune responses. Platelets constitute the principal source of circulating mitochondria, and increasing evidence demonstrates that they actively release mitochondria, some of which are enclosed within extracellular vesicles. This process is enhanced in autoimmune conditions, occurs in platelet storage, and has been linked to adverse reactions after platelet transfusion. Extracellular mitochondria act as carriers of damage-associated molecular patterns and are targets of antibodies in various pathologies, including antiphospholipid syndrome and cardiomyopathies. Moreover, elevated levels of antimitochondria antibodies have also been associated with increased mortality and cardiovascular risk in systemic lupus erythematosus. Mitochondrial transplantation, a process by which defective mitochondria in a tissue or organ may be replaced by healthy mitochondria, is receiving growing therapeutic interest. Thus, understanding how extracellular mitochondria interact with the immune system is increasingly important. This review summarizes current knowledge on the multifaceted roles of mitochondria in immunity, with a particular focus on platelets and platelet-derived mitochondria as a key biological context.