Last revised by Daniel J Bell on 11 Oct 2021

The human body regularly encounters harmful micro-organisms, and because of this it has developed a system of defenses to help identify and eliminate infective pathogens in the body, known as immunity, executed by the immune system. This system also contributes to antioncogenic mechanisms.

Types of immunity

Humans have two types of immunity: innate immunity and acquired immunity.

  1. innate immune system (also known as the non-specific immune system) is the frontline of defense against potentially harmful pathogens. Mediators of the innate immune system include phagocytes such as dendritic cells and macrophages.
  2. acquired immune system (also known as the specific immune system) deals mainly with infections in the later stages, as well as forming what is known as “immunological memory”, which helps the body to remember certain pathogens and how to combat them. Acquired immunity is unique due to its specificity. It develops from lymphocytes that have receptors which are antigen-specific.
Pattern recognition receptors

Innate immunity is not altogether non-specific, as it has the ability to discriminate between normal cells and a wide range of pathogens. The innate immune system has the ability to recognize these pathogens through pattern recognition receptors (PRRs). These PRRs are small in number, when compared to the many receptors used by the acquired immune system.

All pattern recognition receptors share the same characteristics:

  • a major characteristic of pattern recognition receptors is the ability to pick up components of microbes knows as pathogen-associated molecular patterns (PAMPs). PAMPs are vital for the survival of these microorganisms. Because of this, they are difficult for the micro-organism to change.
  • these pattern recognition receptors can detect pathogens, regardless of which stage of the life cycle they are in
  • pattern recognition receptors are "germline-encoded, non-clonal, expressed on all cells of a given type, and independent of immunologic memory” 1. Each PRR will react with its specific PAMP, will have its own expression pattern, and activate their specific signaling pathway and antipathogen response. 

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