More information about Immunity and Infection

There are other cells besides the neutrophils and the lymphocytes which are also involved in fighting infection, such as macrophages (which devour bacteria and dead cells) and mast cells that contain, among other things, histamine, which is released under the influence of antibodies and which invokes part of the inflammatory response necessary to overcome the invading pathogen.

While the newborn baby has all the components of the immune system in place, they are immature, and for the first six weeks of life the baby is dependent upon antibodies which have been passed from the mother across the placenta before birth, and secreted in her colostrum - the antibody rich milk which the mother produces in the first few days of lactation. Because the immune system is relatively immature, and because infants and young people have not been exposed to many infections and therefore have no immune memory, once the mother's antibodies have run out - at about 6 weeks - they are at risk of infectious disease. This is the most common disease process of childhood, and worldwide claims the lives of many young people through illnesses such as gastroenteritis and malaria.

There are a number of ways in which children can become infected: they can contract disease before birth if, for example, the mother is suffering from infections such as HIV or hepatitis B; they can inhale infectious agents coughed or sneezed by someone who has them, they can be given it as a present by someone who kisses them, they can ingest them in infected food or they can contract them from the family pet.

Infection causes fever: our body temperature is controlled by a part of the brain called the hypothalamus, and is set at 37 degrees Celsius. Infection by a bacterium or virus causes this thermostat to be reset at a higher level, and our temperature rises, producing fever. This is accompanied by shivering (the repeated muscle contractions contribute to the rise in temperature) headache (because the blood vessels are dilated) and sweating as the body tries to lose heat. A temperature above 40 degrees can produce delirium in the young child, and febrile convulsions in babies, so it is important to reduce the temperature using paracetamol or ibuprofen - which work to re-set the thermostat - and tepid sponging.

Immunity can be boosted by the process of vaccination, in which the body is exposed to a harmless variant of the infectious agent so that the immune system learns to recognise it - and is therefore ready and waiting when the real agent arrives. Vaccination has reduced the incidence of many diseases worldwide, and has resulted in the elimination of smallpox. There are, however, many diseases for which vaccines are not yet available. Vaccination produces active immunity - our immune system is activated. For some diseases immunity can be improved by the use of injections of gammaglobulin extracted from the blood of people with the disease. This is passive immunity, because the gammaglobulin gets degraded over a period of time, and the immune system is not activated