Molecular mechanisms in the pathogenesis of sepsis

Innate immune system is a universal form of host defense against infections. The recognition of the innate immunity is based on a limited number of encoded receptors that have evolved to recognize microbial metabolism products. The recognition of these molecular structures allows the immune system to distinguish its own infectious components from non-communicable structures. The immune suppression is a hallmark of sepsis. The complement system is activated in the early stages of sepsis, generating large amounts of anaphylatoxin C5a. Complement and TLRs (toll-like receptors) family are two major upstream sensors and effectors systems of innate immunity. It was found that TLR4 and complement system are involved in the initiation of the inflammatory response in sepsis. Clinical studies in which TLR4 was blocked have not shown beneficial effects. TLRs, that are a subfamily of PRRs (pattern recognition receptors), have emerged as the crucial receptors for the recognition of DAMPs (Damage-associated molecular pattern molecules). Recently, a special form of non-coding genetic material called microRNA has been highlighted in the complex cascade of sepsis. The individual role of every microRNA and the exact role of microRNA network are under investigation. Currently, studies are performed in order to find micro RNA to be used as biomarkers of sepsis. Researches are performed to determine microRNA, small fragments of non-coding RNA, in order to distinguish between patients with sepsis and healthy patients, and if the plasma levels of microRNA correlate with the severity of the disease. Recent researches report that the regulation of gene expression through microRNA plays a very important role in the following cellular processes, for example: apoptosis, the differentiation process, and the cell cycle.