What happens in the kidneys
In MPGN, a protein called complement gets trapped in the tiny kidney filters (glomeruli). Complement is part of the immune system, which normally protects the body from infection and disease. Doctors think that the complement in the glomeruli is causing the MPGN.
The immune system
Many germs – including bacteria and viruses – can make us sick if they get into the body. The immune system can kill these germs. However, if the immune system is not working properly, it can start to cause problems.
Read more about the immune system
Germs
The immune system protects the body against germs such as bacteria and viruses that can cause illness. These germs can enter the body in lots of ways, such as by the nose and throat or the urinary system. If we get a cold or flu, this means that a virus germ has got into the body and started to infect some of our body’s cells. Germs have special ‘markers’ that are different from the markers on our own body’s cells. This means that the immune system can recognise that they are germs and kill them. We often feel sick for a few days or a few weeks while this is happening.
Parts of the immune system
The immune system has many different ways to protect the body against disease. Some of the parts include those listed below.
- White blood cells are living cells in the blood. Often, the number of white blood cells found in a blood test can give information about someone’s immune system. The two main types of white blood cells in the immune system are neutrophils and lymphocytes.
- Antibodies or immunoglobulins recognise the germs that have come into the body, and can bind (stick) to them. There are five types: immunoglobulin A (IgA), immunoglobulin D (IgD), immunoglobulin E (IgE), immunoglobulin G (IgG) and immunoglobulin M (IgM).
- The complement system is made up of other proteins that float in the blood. These proteins work with (complement) other parts of the immune system to help kill germs or cells infected by germs. Normally, the body controls when complement is activated, so it does not attack the body itself.
When the immune system does not work properly
Sometimes the immune system does not work as expected and can cause problems. For example, sometimes the immune system cannot recognise the body’s own cells and may attack them as if they were invaders like germs.
Types of MPGN
There are three types of MPGN. These are identified by the pattern of complement that is trapped in the glomeruli.
- Type 1 and type 3 are very similar.
- Type 2 is different. It also called dense deposit disease (DDD) because there are dense (thick) deposits of complement trapped in the glomeruli.
The complement system is made up of proteins that work with other parts of the immune system. It is normally only activated (made to work) when it is needed. This happens in different ways.
Read more about types of MPGN and complement
Type 1 and type 3 MPGN
Complement can be activated by antibodies (or immunoglobulins), which the body makes to fight specific germs. The antibodies can direct the complement to work against these germs.
Children with type 1 and type 3 MPGN often have both antibodies and complement deposited in their glomeruli. Doctors think that these antibodies are made to fight an infection and that they activate the complement.
Some of these children may also have low levels of one type of complement called C3.
Type 2 MPGN (dense deposit disease)
Children with type 2 MPGN have complement, but no antibodies, deposited in their glomeruli. Doctors think that the complement is activated by itself, which does not normally happen.
Children with type 2 MPGN often have nephritic factors, which are types of autoantibodies. Instead of working against germs, autoantibodies work against the body’s own proteins. These nephritic factors stop a protein called factor H from working. Because factor H normally controls how complement is activated, these autoantibodies allow the complement to become overactive.
Some of these children have low levels of factor H.
Will it affect other family members?
Doctors do not think that MPGN runs in families. If one of your children has this type of glomerulonephritis, it is unlikely that another of your children or another family member will get it.
Read more about how the kidney works and the immune system
How the kidney works
Inside each kidney, there are about one million nephrons. Each nephron is made up of a glomerulus (when we talk about more than one glomerulus, we say glomeruli), and a renal tubule.
- Each glomerulus acts like a sieve, helping to remove extra water and waste from the body, and holding on to blood cells and protein, which the body needs.
- Blood flows into the kidneys and to each glomerulus.
- Most of the water and some other substances in the blood pass through the glomeruli
- This liquid flows into the renal tubule. Most of this liquid moves back into the bloodstream. The rest of it becomes urine.
- The urine leaves the kidney by the ureters and goes into the bladder, where it is stored until we are ready to go to the toilet.
More about what the kidney does
What happens in MPGN
In MPGN, a protein called complement, which is part of the immune system, gets trapped in the glomeruli. This causes the glomeruli to become inflamed (swollen) or damaged. The damaged glomeruli can let blood cells and protein through, which means they go into the urine.
About the name
Nephritis means inflammation, or swelling, in the kidneys. Glomerulonephritis is specifically about inflammation of the glomeruli.