Innate immunity is the first line of defense against any invading pathogen. Innate immune system is remarkably conserved among animals, plants and insects, suggesting common source of origin and their diversion during the course of evolution. Families of receptors called Toll like receptors are found in every form of life from insects up to mammals. Major signal transduction pathway that activates the Toll-like receptors in mammals are called NF-κβ pathway.

 

3.1 Important functions of innate immunity

Controls and eliminates the infection at the entry point itself.

Eliminate the infected cells and correct the damage by tissue repair.

Stimulates adaptive immune response

 

3.2 Immune response to microbes

The early innate immune response is the first check point for any microbe that enters the body through different portals (skin, blood, aerosol and mucous membrane). If pathogen enters successfully inside the body the innate immune response counter attacks the pathogens. The major way of innate immunity interventions are inflammation and antiviral defense.

3.2.1 Inflammation

Inflammation is the migration of leukocytes , plasma proteins, and blood to the area of breach. They are recruited to the site of injury and destroy the evading pathogens by the help of cytokines and phagocytic cells (neutrophils, macrophages, monocytes). The mechanism of killing may involve formation of free oxygen and nitrogen radical by the phagocytes. The effect of inflammation in the body has some cardinal features which are described as rubor, calor, dolor, tumor, and functio laesa.

Rubor- Redness (because of increased blood supply).

Calor-Heat ((because of increased blood supply).

Dolor- Pain (because of the P substance produced following the secretion of cytokines).

Tumor- swelling (due to accumulation of fluid).

Functio laesa - Loss of function.