Convertase is a complex of enzymes that is part of the complement system. The complement system is in turn an important component of the immune system.
What is convertase?
Convertase is a complex of enzymes that circulate in the blood and is part of the complement system. The complement system is in turn an important component of the immune system. Two different forms of convertase are known. One form is formed via the classical pathway from the complement parts C4b, C2a and C3b. The other form is formed via an alternative pathway from complement factors of the C3b type. However, both forms have the same function. They activate complement factors and thus play an important role in immune defense.
Function and role
Convertase is one of the critical components of the complement system. The complement system belongs to the nonspecific humoral defense of the immune system. The humoral defense system consists of various proteins that circulate perpetually in the blood, lymph, and intercellular fluid. Unlike defense cells, they are not able to actively migrate to a location. The proteins (proteins) are non-specific because they are not directed against a specific type of pathogen. The complement system is a system that also consists of plasma proteins. It is involved in the antibody response on the one hand and in the innate immune system on the other. More than 30 different proteins make up the complement system. They are either dissolved in the blood or bound to cells and are designed to defend against microorganisms such as bacteria, viruses or fungi. The complement system covers the surface of pathogens. In medical terminology, this process is also known as opsonization. Opsonization enables the phagocytes to recognize that a pathogen is involved. Only when a pathogen is opsonized can the phagocytes destroy it. The complement system also triggers various inflammatory responses. This is to support the body in its fight against the pathogens. Parts of some proteins of the complement system also attract further phagocytes to the site of infection. They thus function as chemokines. In addition, the complement proteins are able to destroy bacteria directly. However, in order for the complement system to become active at all, it must be activated. Three different pathways can be distinguished. The end product of all three pathways is convertase, which is formed on the surface of the target cells. The convertase initiates a cleavage cascade. This chemotactically attracts leukocytes (white blood cells), increases the activity of phagocytes, and finally initiates the dissolution (lysis) of the target cell. On the one hand, the complement system can be activated via the classical pathway. Antibodies play an important role in this process. If the system is activated via a mannose-binding lectin, this is referred to as the lectin pathway. The third pathway is the spontaneous and antibody-independent alternative pathway.
Diseases and disorders
Complement proteins activated by convertase have potent cell-destructive properties. When unregulated, for example, when excessively activated by convertase, they can be responsible for tissue damage and cause or negatively affect various diseases. One serious disease in which convertase is involved with the complement system is renal inflammation. It is an inflammation of the renal corpuscles (glomeruli). The inflammation is abacterial, meaning that no pathogens are involved. Rather, glomerulonephritis (kidney inflammation) is an immune reaction that can occur after infection with streptococci. The disease usually affects children between the ages of two and ten. Glomerulonephritis is always preceded by an infection with ß-hemolytic A streptococci. These are usually infections of the upper respiratory tract or the skin. This leads to the formation of antibodies, which are directed on the one hand against structures of the streptococcal surface, but on the other hand also against the body’s own structures of the renal corpuscles. The antibodies circulate in the blood and are then deposited as so-called immune complexes on the renal corpuscles. Immune complexes are complexes of antigens and antibodies. They are formed during an antigen-antibody reaction. As a result of these deposits, various reactions of the immune system occur.Neutrophil granulocytes, a subgroup of white blood cells, migrate into the renal corpuscles and release pro-inflammatory substances. The complement system is then activated. Under the influence of convertase, a lysis complex is formed. This dissolves proteins of the glomerular membrane and thus leads to damage of the membrane. In addition, swelling occurs in the area of the glomeruli. The first symptoms appear one to three weeks after the original infection. Fever, abdominal pain and headache occur. The destruction of the glomerular membrane causes blood and proteins to pass into the urine. This is referred to as hematuria and proteinuria. The loss of protein results in symptoms such as edema. Hypertension may also occur in the course of glomerulonephritis. The complement system is also overactivated with convertase in the course of hemolytic uremic syndrome (HUS). HUS is a disease usually caused by infection with enterohemorrhagic Escherichia coli (EHEC). The bacteria produce the Shiga toxin. This activates the complement system. The disease is characterized by damage to small blood vessels. As a result, large quantities of red blood cells are lost. In addition, there is a decrease in blood platelets (thrombocytes). In the course of the disease, acute kidney failure also occurs. In Germany, hemolytic uremic syndrome is the most common cause of acute kidney failure in children. In its typical form, the disease is accompanied by diarrhea. The atypical form progresses without diarrhea. There is no known causal therapy for the disease. Approximately two to three percent of all HUS cases are fatal.
