Innate immunity: An overview

Innate immunity can be defined as the non-specific immune defences that come in play in case of body invasion by an infectious agent. In the arena of body defence, just like the military organization, there is the first line to be deployed against and infectious agent, in a specific order until the defence of last resort is sought.

The core function of the immune system is to counter the infectious agents that we are exposed to in our daily lives. The exposure could be through what we eat, the air we breathe or even the things we get in contact with such as contaminated open surfaces.

There are two forms of defence in this case; that is innate immunity and adaptive immunity. When it comes to defending the body, innate immunity is considered the first line of defence while the adaptive immunity is the second in line is that it has memory, it tends to be very rigorous in protecting the body in the second invasion by the same pathogen. Even though they are two branches of immunity that look distinct, there is an interplay between them.

The major components of innate immunity include:

  1. Anatomical barriers
  2. Humoral barriers
  3. Cellular barriers

Anatomical Barriers

Anatomical barriers or physiological barriers are those protective layers that depend on body functionality. They include mechanical barriers, chemical factors, and biological factors.

The mechanical factors include the epithelial surface which is very impermeable to many pathogens, for example, the skin. in addition to the epithelia, the movement of cilia prevent the holding of substances along the gastrointestinal tract, of which otherwise could lead to flourishing of microbial colonies; tears and saliva also flash microorganisms off the body surfaces, this together with the mucus that lines the respiratory surfaces and the gastrointestinal tract, help prevent infection on the organs ie the gut and respiratory system.

The chemical factors involved in innate immunity include fatty acids in sweat that inhibit bacterial growth; the lysozymes and phospholipase found in tears and saliva are responsible for breaking down of bacteria cell walls and destabilizing their membranes; the low pH in gastric secretion inhibits growth and colonization by many bacteria types; the lungs have defensins which are low molecular weight proteins that have antimicrobial activity; the surfactants found in the lungs also have opsonizing activity against foreign substances.

The biological factors in innate immunity include the normal flora of the skin and the gastrointestinal tract which prevent colonization by pathogenic bacteria by mounting competition for resources such as food and space through excretion of toxic substances against the pathogenic organisms or phagocytosis.

Humoral Barriers

When the anatomical barriers are breached, what is normally witnessed is acute inflammation. this is also called the humoral reactions. these reactions involve a complex series of enzyme actions and immune reaction systems. therefore, the components of humoral barriers include:

  • The complement system,
  • The coagulation system,
  • Lysozymes,
  • Cytokines,
  • Lactoferrins and transferrins.

Cellular Barriers

When the two aforementioned mechanisms of innate immunity are bypassed by the invading pathogenic organism, the cellular barries is deployed. This form of barrier includes cells that are dedicated to eliminating foreign organisms from the body using different mechanisms nonspecifically. For instance, the invading organism could be eaten by the immune cell, digested and disposed of by the various body mechanisms.

The cells that compose the cellular barriers include:

  • Neutrophils
  • Monocytes
  • Natural killer cells
  • Eosinophils