A complement deficiency is a shortage of key proteins that play a role in the complement system, which is a part of the innate immune system that forms the body's defense against pathogenic organisms. In a person who has this condition, the immune system is less able to mount an effective attack against infection or might be overactive. This can result in increased risk of serious illness and might be fatal if the patient does not receive adequate monitoring and treatment. Tests are available to check for complement deficiencies if a doctor suspects that they might be an issue.
This component of the innate immune system assists in immune responses. When it does not function properly, it can turn a simple infection into a very serious one. It also can trigger widespread inflammation in response to a relatively minor issue. In some cases, this results in the development of a chronic autoimmune disease.
Some patients who have a complement deficiency experience problems with the activator proteins in the complement system. When the body is exposed to a potential source of illness, the immune system normally begins a cascading series of reactions. In a patient who doesn't have the right proteins, the complement system does not activate, and the patient is less able to fight the infection.
On the other end, some patients don't have functioning inhibitor proteins. These proteins normally keep the complement system in check and prevent overreactions. When they are not present or do not work properly, the immune system can go into overdrive in response to potential threats. This can trigger a systemic inflammatory reaction. Conditions such as systemic lupus erythematosus are the result of a complement deficiency.
Inherited complement deficiencies can be seen in some populations. These genes typically are recessive, and a patient needs two copies for the condition to express. Some are X-linked and are more common in men, because they lack the corresponding healthy genes on the Y chromosome to make up for defective genes inherited from their mothers. It also is possible to acquire a complement deficiency. Researchers who have an interest in immune disorders study patients with conditions such as lupus to learn more about their causes and develop effective treatments.
Treatment options in the short term for a patient who has a complement deficiency can include fresh frozen plasma (FFP) to provide the patient with the necessary proteins. Patients might also need to take prophylactic medications for life to address the issue. Some patients also benefit from vaccination to reduce the risk of becoming seriously ill as a result of a routine infection.
