Clinical immunology involves the investigation, diagnosis and management of diseases associated with abnormalities in the immune system. The most common problems are overactivity of the immune response leading to allergic and autoimmune disease, or underactivity resulting in immunodeficiency.
Host defence mechanisms
The immune system is made up of a complex network of cells, humoral factors and soluble messengers or cytokines, which confer protection against disease. However, other mechanisms are also important in defence. Several factors can reduce the effectiveness of this ‘first line’ of defence:
1 Breach of skin/mucous membrane integrity due to trauma, burns, eczema
2 Suppression of cough reflex due to opiates, neurological disease
3 Failure of respiratory mucus clearance
(a) Smoking (ciliary paralysis)
(b) Primary ciliary dyskinesis syndromes
(c) Increased mucus production (asthma)
(d) Abnormally viscid secretions (cystic fibrosis)
4 Loss of colonization resistance-use of broad-spectrum antibiotics.
In these situations pathogenic organisms may gain access and cause disease, despite a normal immune system.