The body’s highly complex system (made up of cells, tissues and organs) that defends the body against infection, disease, and other foreign substances.
White blood cells (leukocytes), antibodies, the thymus, spleen, tonsils, lymph nodes, lymph vessels, and bone marrow are part of the immune system.
There are two ways in which the body protects us from harmful organisms:
- Innate immunity, the body’s first line of defence, responds generally and immediately when a pathogen or foreign substance enters the body. It includes the skin (a barrier that keeps out pathogens) and the mucous membranes of the digestive, reproductive and respiratory tracts.
- Adaptive immunity, the body’s second line of defence, is activated over time when innate defences fail. Adaptive immunity is able to keep a record or memory of every pathogen it has defeated so that it can recognise and destroy those specific pathogens quickly if they enter the body in the future (reinfection). This means the body becomes immune to those pathogens. Vaccines use adaptive immunity and memory to expose the body to an antigen without causing disease. See B-cells and T-cells.
Immune System Infectious Disease Vaccines