Types of Immunity - Innate Immunity

Innate immunity:

• Innate immunity is the natural phenomenon of resistance to infection which an individual possesses right from birth.
• The innate defense mechanisms are non-specific in the sense that they are effective against a wide range of potentially infectious agents.
• It is otherwise known as non-specific immunity or natural immunity.
• A number of innate defense mechanisms are operative non-specifically against a large number of microorganisms.
  

  Various anatomical and physiological barriers to microbial attack

Type of innate immunity:

Innate immunity consists of four types of barriers. These are -

1. Anatomical barriers (Physical barriers):

• Skin: The skin on our body is the main barrier which prevents entry of the microorganisms. Its acidic environment (pH 3-5) retards the growth of microbes.
• Mucus membrane: Mucus coating of the epithelium lining the respiratory, gastrointestinal, and urogenital tracts also helps in trapping microbes entering our body.

2. Physiological barriers:

• Temperature: Normal body temperature inhibits the growth of pathogens. Fever also inhibits the growth of pathogens.
• Low pH: Acidity of gastric secretions (HCl) kills most ingested microbes.
• Chemical mediators: Lysozyme acts as an antibacterial agent and cleaves the bacterial cell wall. Interferons induce an antiviral state in the uninfected cells. Complementary substances produced from leucocytes lyse the pathogenic microbes or facilitate phagocytosis.

3. Phagocytic barriers (Cellular barriers): Certain types of leukocytes (WBC) of our body like polymorpho-nuclear leukocytes (PMNL - neutrophils) and monocytes and natural killer (type of lymphocytes) in the blood, as well as macrophages in tissues, can phagocytose and destroy microbes.

4. Inflammatory barriers: Tissue damage and infection induce leakage of vascular fluid, containing chemotactic signals like serotonin, histamine, and prostaglandins. They influx the phagocytic cells into the affected area. This phenomenon is called diapedesis.

5. Cytokine barriers: Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.