Inflammatory

Interleukin-6 (IL-6), also known as B-cell stimulatory factor 2 (BSF-2), is a multifunctional cytokine. The human IL-6 gene is located on chromosome 7 and is approximately 5kb long, with five exons and four introns. The human IL-6 molecule consists of 212 amino acid residues, including a signal sequence of 28 amino acid residues. Mature IL-6 consists of 184 amino acid residues and has a molecular weight of 26kDa. IL-6 plays a central role in acute inflammatory responses and is directly related to inflammatory diseases and the degree of infection. In the "Expert Consensus on the Clinical Significance of Infection-related Biomarkers" (2017), it was pointed out that IL-6 can be used to assist in the early diagnosis of acute infections in the diagnosis of inflammation; IL-6 can be used to evaluate the severity of infection and predict prognosis; dynamic observation of IL-6 levels can also help understand the progression of infectious diseases and the response to treatment. At the same time, the serum concentration level of IL-6 increases earlier than PCT and CRP. Combined detection of IL-6 and PCT can help doctors diagnose, evaluate the condition, guide treatment, and reduce unnecessary use of antibiotics.

Serum amyloid A protein (SAA) is an acute-phase reactant protein and a heterogeneous protein in the apolipoprotein family. There are four serum amyloid A protein genes in the human body, SAA1-SAA4. SAA1 and SAA2 are two proteins in the acute phase called A-SAA, with a difference of seven amino acids between the two proteins. SAA3 is a hypothetical gene that does not translate into protein, and SAA4 is a constitutive protein that has always existed in cells. Like C-reactive protein (CRP), the concentration of serum amyloid A protein is a sensitive indicator of early inflammation in infectious diseases. There is one important difference: SAA increases significantly during viral infections, while CRP does not increase or only increases slightly within a narrow range in viral infections without bacterial infections. Therefore, SAA can be used for the diagnosis of viral infections. For transplant rejection, SAA testing is a fairly sensitive indicator. In irreversible transplant rejection testing, its average concentration is higher than that of reversible rejection cases. The chronic increase in SAA concentration in patients with rheumatoid arthritis, tuberculosis or leprosy is a prerequisite for the synthesis of AA-amyloid fibers, which is also used to diagnose secondary amyloidosis. Combined detection of SAA and CRP can better reflect complementary advantages and provide more evidence for the diagnosis and differential diagnosis of bacterial and viral infections. The ratio of SAA/CRP can better reflect the clinical significance that single indicators cannot reflect. It guides the use of antibiotics in the treatment of chronic obstructive pulmonary disease. Combined detection of SAA and CRP can help diagnose infectious diseases in children early by compensating for the insignificant differences in CRP levels during viral infections. CRP+SAA combined detection is also a sensitive indicator for early diagnosis, efficacy and prognosis evaluation of hospital infections in gynecological chemotherapy patients.

C-reactive protein (CRP) is part of the body's non-specific immune mechanism and is an acute-phase protein synthesized by the body in response to inflammatory stimuli such as microbial invasion or tissue damage. The full length of human C-reactive protein is 224 amino acids. The protein is produced in the liver and distributed in plasma, generally in the form of a pentamer in plasma. Routine C-reactive protein testing plays an important role in determining the degree of bacterial or viral infection, treatment efficacy and prognosis. The detection of high-sensitivity C-reactive protein (hs-CRP) is of great significance for evaluating the risk of cardiovascular and cerebrovascular diseases.

Procalcitonin (PCT) is a protein composed of 116 amino acids with a molecular weight of approximately 13 kDa. It is the precursor of calcitonin (CT) and has no calcitonin-like hormone activity. Its molecule consists of calcitonin, calcitonin gene-related peptide and a 57-amino acid N-terminal fragment. PCT is mainly synthesized in the parafollicular cells of the thyroid gland and can also originate from neuroendocrine cells in the lungs and small intestine. The PCT content in normal human serum is extremely low (<0.05 mg/L), but when certain pathological conditions occur, bacterial endotoxins, TNF-α, IL-6 and other factors act on neuroendocrine cells or special cells in the liver, spleen, kidney and lungs to produce it, which can increase to more than 100mg/L. PCT is a new and innovative ideal indicator for diagnosing and monitoring severe bacterial infections, sepsis and other diseases. Because PCT concentration does not increase or only slightly increases in local infections, viral infections, chronic nonspecific inflammation, cancer fever, transplant host rejection reactions or autoimmune diseases, it only significantly increases in severe systemic infections. Therefore, PCT is a better tool than CRP, IL-6, body temperature, white blood cell count and erythrocyte sedimentation rate for monitoring severe infections. This determines the high specificity of PCT and can also be used for differential diagnosis of various clinical situations.

Heparin-binding protein (HBP), also known as azurocidin, is a member of the serine protease family. Its structure is similar to that of elastase, but it does not have protease activity. Because HBP is mainly released by neutrophilic segmented cells under external stimuli, the HBP content in normal human blood is very low. When an infection occurs, some bacteria invade the blood vessels, and substances such as the bacterial body itself or toxins released by bacteria stimulate neutrophils to release HBP, which leads to an increase in the HBP content in the blood. HBP can be used for the auxiliary diagnosis and differential diagnosis of infectious diseases, evaluation of the severity of infection, prediction of sepsis, hypotension, organ functional disorders, diagnosis of sepsis, prognosis evaluation of sepsis and so on. The concentration of HBP can be measured in patients within 72 hours before sepsis occurs; most patients have an increase in HBP concentration before sepsis occurs within 10.5 hours (median). Compared with other biomarkers, HBP has important significance for early diagnosis and prediction of sepsis and is the only predictive indicator for sepsis. It has been included in guidelines and expert consensus such as "China Severe Sepsis/Sepsis Shock Treatment Guidelines (2014)" and "Expert Consensus on Early Prevention and Diagnosis of Sepsis 2020", which recommend the clinical significance of HBP in the diagnosis and treatment and prediction of sepsis.

Protease serine 2 (PRSS2) is a protein with a relative molecular mass of 25kD. The vast majority of it is secreted into the pancreatic juice in the form of pancreatic acinar cell protease precursor and is activated by intestinal enzymes in the intestine to become an activator of other highly active digestive enzymes. The level of PRSS2 in the pancreas is very high, but the level of PRSS2 in the blood is very low because only a small amount leaks into the blood circulation under normal circumstances. When pancreatic tissue is damaged, PRSS2 is released into the blood in large quantities, filtered through the glomerulus, and PRSS2 is rarely reabsorbed and excreted in large amounts with urine. The concentration of PRSS2 in urine is consistent with the severity of pancreatic tissue damage.

Calprotectin is a calcium- and zinc-binding protein complex of S100A8 and S100A9, which is a calcium- and zinc-binding protein derived from neutrophils and macrophages. Its expression has tissue or cell specificity. The molecular weight is 36 kDa. It is composed of an isotrimer of two heavy chains with a molecular weight of 14 kD and a light chain with a molecular weight of 8 kD connected by covalent bonds. Each chain can bind two calcium ions, thus having the characteristics of heat resistance and enhanced hydrolysis. It can be used as a marker for acute inflammatory cell activation.