The innate immune system is a ” hard-wired” defense that has evolved over millions of years to recognize pathogens that commonly infect humans. The innate system team includes the complement system of proteins, the professional phagocytes and natural killer cells. These warriors must be activated before they can fight.
The complement system must be activated before it can function, and there are three ways this can happen: the classical pathway that depends on antibodies for activation, activating the alternative pathway that simply require that a complement protein fragment C3b binds to an amino or hydroxyl group on an invader, and the lectin activation pathway which uses a protein called mannose-binding lectin that attach to mannose, a carbohydrate molecule found on the surface of common pathogens. The professional phagocytes comprise the second arm of the innate system and include manly macrophages and neutrophils. These professional phagocytes can exist in different states such as resting or active states.
Macrophages in resting state just eat dead cells and debris but become activated when they find an invader and can present antigens to T cells, send signals that recruit other immune system cells and can even become vicious killers. Neutrophils are found in blood and they use adhesion molecules to exit blood vessels at sites of inflammation where the kill invaders. Natural killer cells ( NK cells) secrete cytokines which affect the function of both the innate and adaptive immune system. They can also destroy infected cells. The immune system is programmed to react to danger signals that are characteristic of commonly encountered pathogens. In order to do so, the immune system cells are equipped with pattern recognition receptors that detect common signatures of whole classes of bacteria and viruses. When these danger signals are detected , macrophages respond by producing battle cytokines that alert other cells and prepare them to repulse the attack.
For instance, in response to a viral infection the pattern recognition receptor cells in the body can trigger the production of interferon alpha and interferon beta. In conclusion, the members of the innate system team must work together in order to provide a fast and effective response to common invaders.