2. Specific Immunity to infection – the attacking arm
If the initial innate response to a foreign invader (such as a disease causing pathogen) fails, the acquired immune system takes over. This complex system consists of many interrelated components. Two key elements are:
- B-cells which produce specific proteins called antibodies that neutralise the invader
- T-cells that attack the invader or regulate responses of other immune cells
There are many different T-cells, but important groups are:
- Killer cells destroy pathogen-infected cells and other ‘foreign’ cells
- Helper T-cells (Th) are regulators of cellular immunity.
The attacking arm of the immune system develops in response to exposure to harmful microbes that cause it to react in several ways, most particularly by generating specific antibodies which recognize and neutralise the pathogen. After recovery, the immune system retains memory cells that persist in the body. If re-exposed to the same pathogen, the system mounts the same response to fight off infection. This is the basis of vaccination where the vaccine stimulates antibody production without causing disease symptoms.
Developing specific immunity to a particular diseases (e.g. chicken pox, measles, flu) results from catching that disease or being vaccinated against it. We are also probably exposed to small doses of various pathogens in our daily lives – large enough to develop immunity but too small to overwhelm the immune system and make us ill.
Vaccination
After recovery from an infection, the body retains some of the B and T lymphocytes (known as memory cells) which persist in the blood and lymph systems. If re-exposed to the same antigen threat, the memory cells mount a strong rapid immune response.
This is the basis of vaccination e.g. flu virus, treated to destroy their disease causing properties but not their antigenic properties, are injected to induce permanent resistance to the strain of flu.
