1. Hypersensitivity
This occurs when the immune system over-reacts to things! Allergies, such as asthma and hay fever, are examples of hypersensitivity.
Who's responsible for this??...
Here's what happens....
Autoimmune diseases are also caused by hypersensitivity. The immune system no longer recognises 'self' antigens, and attacks the body.
The antigens involved in two autoimmune diseases are:
(Don't worry, I'd never heard of "Systemic lupus erythematosus" either! It's actually an inflammatory disease of the connective tissue.)
Rheumatoid arthritis causes swollen joints. Now, another group of diseases caused by an over-active immune system are caused by "Delayed Hypersensitivity". Hmm. What does it all mean? Have I ever told you about Mycobacteria?
These bacteria are really cunning, they've got escape mechanisms to avoid being killed! You can imagine how frustrating that must be for our phagocytes, who cannot digest them. Our bodies therefore produce "granulomas" to isolate the infected phagocytes from the rest of the body! This is a cause of leprosy.
We're all familiar with rhesus disease, aren't we? This is the Haemolytic Disease of the Newborn. (HDN) It occurs when the mother of a newborn child mounts an immunogical attack against her child because the paternal rhesus blood group is different from her own. Maternal antibodies cause lysis of the child's red blood cells. Poor lamb.
2. Immunodeficiency Diseases
These are caused by immune failure. Our immune systems no longer protect us against microorganisms, leaving us immunocompromised and prone to life-threatening infections.
They fall into two categories:
1. Primary
These occur when the cells of the immune system simply don't develop. Some are also due to defects in the production of molecules
2. Secondary, or "Acquired"
These are due to supression of the immune system. This is caused either by infectious agents such as HIV, or by drug treatments for cancer or for the prevention of graft rejection.
