Innate Immunity

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innate immunity, natural, non-specific

Innate Immunity since Born
Image credit: Microsoft

Innate immunity is also called as non-specific immune system or natural immunity. It is innate where every individual is born with it. Innate immunity consists of four types of defensive barrier such as:

  1. Anatomic
  2. Physiologic
  3. Phagocytic
  4. Inflammatory


Anatomic barrier

Anatomic and physical barrier act as the first line defense system to prevent the entry of pathogen into human body. Two types of barrier are skin and mucosa membrane.

Skin has two layers: epidermis and dermis. Epidermis contains several layers of epithelial cells and outer layer is covered by keratin. Dermis has connective tissues which composes of blood vessels, hair follicles, sebaceous glands and sweat glands. Sebum is secreted by sebaceous glands to maintain the skin pH between 3 and 5. It inhibits the growth of some microorganisms. Acne is formed when the sebum is metabolized by few types of bacteria.

Skin injury

Image credit: Microsoft

The microorganisms able to penetrate the skin layer when there is scratches, wound, abrasion

or bitten by insects such as mites, mosquitoes, sand flies etc. For example, protozoan malaria  is deposited into human body when the mosquito bite the human body to get the blood meal.

Mucous membrane is the membrane covers basically respiratory tract, digestive system and urogenital system. Mucus is secreted to trap the microorganisms. It is helped by the beating cilia. Saliva and tears help to flush away the microorganisms to adhere to the mucous membrane.

Normal flora protect the host by competing with pathogenic bacteria. They also produce antibacterial substances.

Physiologic Barrier

Physiologic barrier includes temperature, pH and chemical mediators.  Some microorganisms are not able to survive in certain range of temperature. Stomach has acidic environment which kill certain microorganisms. Chemical mediator, for example lysozyme has hydrolytic enzyme able to digest or lysis the cell wall of bacteria.

Phagocytic barrier

Phagocytosis is an endocytosis process where the phagocyte cells ingest the extracellular particles and digest it. Phagocyte cells are neutrophil, macrophage and dendritic cells.

Inflammatory Response

Inflammatory response is triggered when pathogenic microorganisms invade the skin damage wound. It causes the complex event. The end functions of inflammation is to clear the invading microorganisms.

The major events of inflammation are as below:

  1. Vasodilation – Increase the diameter of capillaries. It causes tissue redness and increase temperature.
  2. Increase capillaries permeability –  It helps the influx of fluid and white blood cells into damage tissue. The influx of fluid into tissue causes edema.
  3. Influx of phagocytes followed by increase capillaries permeability.