Immunity is the ability to resist a specific infectious disease, meaning you can be exposed to the pathogen that causes it without becoming infected or falling seriously ill. It develops when the cells of your immune system encounter a harmful pathogen - such as a virus or bacterium - mount an immune response, and successfully fight it off. This can happen through infection with the actual disease (natural immunity), or through the introduction of a killed or weakened form of the disease-causing pathogen, or fragment of it, in the case of immunisation (vaccine-induced immunity). This immunity persists because even after the pathogen is eliminated from your body, specialised ‘memory cells’ linger, ready to spring into action and launch an enhanced response against that pathogen if you encounter it again.
There are two broad types of immune response:
(i) Innate responses kick in from the moment of infection and are the same for all potential invaders. They include physical barriers, such as the skin, as well as the activities of immune cells, such as macrophages and natural killer cells, which work to contain invaders while a more targeted ‘adaptive’ immune response develops, and alert other immune cells to their presence. In some cases, a strong innate response is enough to contain and eliminate an invading pathogen, such as a virus, before these adaptive responses kick in.
(ii)Adaptive responses target specific pathogens or foreign substances and can take several days to develop. They involve two types of cells:
- Immune B cells:, which help to hunt down invaders circulating in the bloodstream by producing antibodies - proteins which can bind to e.g. viral particles and either neutralise or mark them for destruction by other immune cells.
- T cells, which seek out and destroy cells that have been infected by the invading pathogen by recognising tell-tale proteins on their surface. T cells also support B cells, helping to control the antibody response.
Who is at risk for immunodeficiency disorders?
People who have a family history of primary immunodeficiency disorders have a higher-than-normal risk for developing primary disorders.
Anything that weakens your immune system can lead to a secondary immunodeficiency disorder. For example, exposure to bodily fluids infected with HIV, or removing the spleen can be causes.
Spleen removal may be necessary because of conditions like cirrhosis of the liver, sickle cell anemia, or trauma to the spleen.
Aging also weakens your immune system. As you age, some of the organs that produce white blood cells shrink and produce fewer of them.
Proteins are important for your immunity. Not enough protein in your diet can weaken your immune system.
Your body also produces proteins when you sleep that help your body fight infection. For this reason, lack of sleep reduces your immune defenses. Cancers and chemotherapy drugs can also reduce your immunity.
The following diseases and conditions are linked to primary immunodeficiency disorders:
ataxia-telangiectasia
Chediak-Higashi syndrome
combined immunodeficiency disease
complement deficiencies
DiGeorge syndrome
hypogammaglobulinemia
Job syndrome
leukocyte adhesion defects
panhypogammaglobulinemia
Bruton’s disease
congenital agammaglobulinemia
selective deficiency of IgA
Wiskott-Aldrich syndrome
