What Is The Function Of Complement Proteins – A series of about 20 types of soluble proteins, called the complement system, work to destroy extracellular pathogens. Liver cells and macrophages are constantly synthesizing complement proteins. These proteins are abundant in blood serum and are able to respond directly to infectious microorganisms. The complement system is so named because it is complementary to the antibody response of the adaptive immune system. Complement proteins bind to the surfaces of microorganisms and are particularly attracted to pathogens that are already bound by antibodies. Binding of complement proteins occurs in a specific and highly regulated sequence, with each successive protein activated by cleavage and/or structural changes induced upon binding of the preceding proteins. After binding of the first complement proteins, a cascade of sequential binding events ensues in which the pathogen rapidly coats complement proteins.
Complement proteins perform several functions. The proteins serve as a marker to indicate the presence of a pathogen to phagocytic cells, such as macrophages and B cells, and enhance stress. this process is called opsonization. Opsonization refers to an immune process where particles such as bacteria are targeted for destruction by an immune system cell known as a phagocyte. Certain complement proteins can combine to form attack complexes that open pores in microbial cell membranes. These structures destroy pathogens by leaking their contents, as shown in Figure 1.
- 1 What Is The Function Of Complement Proteins
- 2 Complement Fixation Test Principle, Procedure, Results, Types
- 3 The Role Of Complement In Kidney Disease
What Is The Function Of Complement Proteins
Figure 1. Click for larger image. The classical pathway for the complement cascade involves binding of several initial complement proteins to an antibody-bound pathogen followed by rapid activation and sequestration of many more complement proteins and generation of destructive pores in the microbial cell envelope and cell wall. The alternative pathway does not involve antibody activation. In contrast, C3 convertase spontaneously cleaves C3. Endogenous regulatory proteins prevent the complement complex from binding to host cells. Pathogens lacking these regulatory proteins are lysed. (credit: work modified by NIH) A study was coordinated to determine the steps in the activation of the complement pathway. In one part of the study, bacteria were added to a blood sample. It was noted that the mannose on the surface of the bacteria led to the activation of a certain protein in the blood involved in the complement system. Which of the following steps does this activated protein follow?
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The complement system refers to a group of plasma proteins called complement proteins, which are produced in the liver and act collectively to help destroy pathogens. Think of them as a small militia that “complements” the work of the antibodies.
There are actually three complementary pathways: the classical pathway – so called because it was discovered first, the alternative pathway which was found second and is always in operation, and the lectin binding pathway – which was found third and when people got more descriptive with their nomenclature.
So let’s start with the proteins that make up the classical pathway – C1, C2, C3, C4, C5, C6, C7, C8 and C9. Easy enough right?
Now these were numbered, in the order in which they were discovered, but not in the order in which they function.
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In general, each complement protein is normally inactive and becomes active when it is broken down – in other words when a part of it is released. Kind of like how a fire extinguisher isn’t “on” until it pulls a pin.
It has six C1q subunits, which are capable of binding to the Fc portion of an antibody when it binds to antigen.
C1q has zero enzymatic activity and typically the serine proteases C1s and C1r are hidden so they cannot perform their enzymatic activity.
All of these are tied together in a calcium arc, so when there is a lack of calcium, C1 is also lacking.
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When 2 or more of the C1q moieties bind to the Fc receptors of 2 or more antigen-bound antibodies, a conformational change is induced in the C1 molecule that twists, exposing the C1s and C1r serine protease sites. Kind of like pulling the safety cover off a pair of scissors.
This time, C2a floats away and C2b joins C4b on the surface of the pathogen forming a protein complex called C4b2b or C3 convertase.
Now this is the step that really kicks things up a notch. This is because a single C1 can make maybe 10 C3 convertases, but a single C3 convertase can break down over 1000 C3 proteins per second, and this enzyme stays active for about 2 minutes, so you will get a lot of C3b very quickly.
C3b is also called an opsonin, and opsonins in general are great because they help phagocytes get a firm grip on bacteria.
Complement Fixation Test Principle, Procedure, Results, Types
The complement system is a group of proteins that help the body fight infection. The complement system has three pathways: classical, alternative, and lectin pathways. The classical pathway is activated by antibodies, and the alternative pathway and the lectin pathway are activated by molecules called pathogen-associated molecular patterns (PAMPs).
The complement system can kill bacteria, viruses, or other cells that have been damaged or invaded by pathogens. They also promote inflammation, which helps further activate the immune system and remove pathogens and debris.
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The complement system is part of your body’s immune system that cleans up damaged cells, helps your body heal after injury or infection, and destroys tiny organisms like bacteria that make you sick. Your supplement is the first line of defense for your immune system.
Your body’s complement system gets its name because it “supplements” or strengthens your body’s cells and infection-fighting cells.
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The complement system is a connection to your body’s defense system to protect you from anything that can harm your body. One of the most common things your complement system does when it activates your immune system is to protect your body from foreign invaders like bacteria that cause infection or disease.
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Plasma proteins, found in your blood and seen under a microscope, make up your complement system. You have about 50 plasma proteins in your body’s complement system.
The proteins that make up your complement system are inactive or turned off until a trigger activates them. Triggers can include injury to your body or bacteria entering your body. Proteins are activated in a domino-like line. One protein will be activated, which triggers the next protein in line to be activated, just like how one domino falls on another domino to create a chain reaction. This chain reaction is called a cascade. When each protein is activated, it can perform its function to protect your body and activate the next one.
The proteins that make up your body’s complement system are made in your liver and travel to your tissues and blood.
About 50 proteins make up your body’s complement system. These proteins circulate throughout your blood and tissues. When the proteins are activated or activated, they attach to foreign invaders and work to destroy them to prevent a disease or injury from harming you.
The Role Of Complement In Kidney Disease
The complement system is an important part of your immune system and works to prevent infection and disease. If your complement proteins don’t work as expected, or if you don’t have enough of them (complement deficiency), you’re considered immunocompromised and your body is at risk of infections that can be very serious (sepsis).
If your supplement proteins are working too hard and activated too often, you may be at risk for several autoimmune or inflammatory conditions. Common conditions in which your complement system may be involved include:
If your complement system is not working properly, your immune system will be weaker than it should be. Symptoms of complement system conditions include:
A complement test is a blood test where a blood sample is taken from your vein that measures the amount and function of proteins in your complement system. Complement tests can measure proteins individually or in total to look for any weakness or overactivity. Additional tests help identify:
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Other important tests if your immune system is not working properly include a complete blood count and immunoglobulin (antibody) levels.
Treatments for diseases of the complement system focus on managing symptoms and treating the underlying complement deficiency or overactivity. Treatment options include:
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