IMMUNOLOGY SERIES- PART 3- MECHANISMS OF INNATE IMMUNITY

A detailed description of innate immunity has been provided in the previous article. This article explains in detail the action of innate immunity. As mentioned earlier, innate immunity is a non-specific immunity that acts as the first line of defence. There are six mechanisms backing innate immunity. They are:-

  1. Epithelial surfaces
  2. Antimicrobial products
  3. Microbial antagonism
  4. Cellular factors
  5. Inflammation
  6. Acute phase proteins

These are the six different mechanisms of innate immunity.

Epithelial surfaces

The epithelial surfaces are those which form the outermost layer of the body. It is pretty obvious that the pathogens gain access into the body through the body openings. Hence it is trivial that the immunity is strong at these places. The following are the body openings where the immunity is present:-

  • Eyes
  • Ears
  • Nose
  • Mouth
  • Skin
  • Genital tracts

Eyes– there is a special fluid called the ‘tear’ generated by the lacrimal apparatus. This tear can flush out the microbes by its mechanical action. Also, the enzyme called lysozyme is present in it which is antibacterial in nature. This particular enzyme splits certain polysaccharide molecules from the cell wall of the bacteria without which it cannot sustain. Hence these are processes that confer immunity to the eyes.

Ears– there is a constant production of wax that entraps the foreign microbes. The cells lining the outer surface of the ear membranes secrete the wax for cleaning and protective purposes. The inner ear is filled with phagocytic cells.

Nose– the nose and the respiratory pathway are very important to be protected since they involve the exchange of air and microbes can easily enter. So there is tightened defence provided by several mechanisms:-

  • The anatomy of the nose itself prevents the entry of some microorganisms
  • There is mucus lining the entire respiratory pathway which have hairs that can sweep the microbes back to the air
  • There are mucopolysaccharides which are sticky in nature and hence the microbes get stuck to them
  • The alveoli of the lungs are filled with phagocytic cells

Mouth– the mouth and the digestive system are also as important as the nose. The following defence mechanisms can be seen

  • Saliva which is basic in nature kills some of the pathogens
  • The peristalsis movement can kick away some of the microbes
  • The stomach acid which is low in Ph can destroy most of the microbes
  • The digestive juices and secretions like the bile also provide immunity

Skin- the skin is present all over the body and there are 4 mechanisms

  • Long chain fatty acid
  • Salty nature of the sweat
  • Soaps contribution
  • Oils and sebaceous glands

Genital tract- this is also an important opening to be concerned about as there is a large concentration of microbes found here. The urine itself flushes out any incoming pathogens. In males, the sperm protein spermine and zinc are antibacterial. In females, high acidity can kill the microbes.

Antimicrobial products

There are some anti-microbial products present naturally in the bloodstream and other body fluids.

  • Beta lysine- effective against thermostable bacteris
  • Polypeptides- leukin and plakin
  • Lactic acid- muscles
  • Lactoperoxidase- present in breast milk
  • Interferons- effective against virus

Microbial antagonism

Remember the fact in the first article that the foreign microbe has to find a suitable ‘target site’. The reason is that there are already some microbes present inside us. Don’t worry they won’t hurt us. These microbes constitute the normal flora and are resident. They follow symbiotic relationships with us. A suitable example is an e.coli present in the intestine helping indigestion for food.

So the presence of one species of organisms do not allow the presence of similar or different species. So these microbes indirectly furnish immunity to the body. So nice of them!

Cellular factors

These are some cells that are specialised in the function of protecting the body by destroying pathogens. It is done by the process of phagocytosis which is the engulfing of substances. The phagocytising cells engulf the foreign particles in response to the chemical mediators (mediators are certain chemicals released by a special type of immune cell known as mast cell).

There is a special defence for viral infections. In this case, the interferons activate the NK cells (Natural Killer) to undergo phagocytosis. This cell can be called the assassin of the immune system.

Inflammation

Inflammation is one of the body’s responses to the invasion of foreign particles. This is an important process in the human body that occurs to drive away from the pathogen. Inflammation is one of the stages seen in healing. This inflammation can be either acute or chronic. Acute stay for a shorter time but produces more vigorous pain whereas chronic stays for a longer time with less vigorous pain. If the causative agent has been driven away then healing occurs either by complete restoration or scar formation. There are chances that the acute inflammation can become chronic which can be worse. It can lead to several diseases and complications.

Acute-phase proteins

These are certain indicator proteins present in the blood whose increase in the level indicates infections. A group of these proteins constitute the acute phase proteins. They are:-

  • C-reactive protein
  • Mannose binding factor
  • Serum P amyloid component
  • Alpha -1-acid antitrypsin

These proteins enhance the defence and host resistance, prevent tissue injury and aid in damage repairs.

The next article deals in detail with another type of immunity, the acquired immunity.

HAPPY READING!!!