Immune system acts as the body’s defence system against foreign particles and pathogens. It recognizes and attacks pathogens so that we do not get ill, and stay healthy. There are two main types of immune systems: innate and adaptive immune systems.
The innate immune system acts as the first line of defence against such pathogens that are foreign and non-specific. This innate immunity provides a quick response against the foreign pathogens, and restricts the entry and spread into the body. In the innate immune system, the skin, mucus membrane and innate immune cells play an important role. The immune cells like phagocytes, dendritic cells and natural killer cells mount an immune response against non-self pathogens. Also, complement proteins found in the blood can attack bacteria so that they do not cause disease.
On the other hand, the adaptive immune system acts as the second line of defence against the foreign pathogens but is very much specific. Also, adaptive immunity has memory which means exposure to repeated pathogens can cause vigorous immune responses. The main cells involved are called B-lymphocytes and T-lymphocytes. The B cells once recognize a pathogen; will form mature B cells that will release specific antibodies to kill that one type of pathogen. T-cells can also mount an immune attack; resulting the pathogens to get killed.