• Clinical science

Innate immune system

Abstract

The innate immune system provides a non-specific first line of defense against pathogens. It comprises physical barriers (e.g. the skin) and both cellular (granulocytes, natural killer cells) and humoral (complement system) defense mechanisms. The reaction of the innate immune system is immediate, but unlike the adaptive immune system, it does not provide permanent immunity against pathogens.

Overview

Definition

The innate immune response is composed of physical, chemical, cellular, and humoral defense mechanisms against pathogens. It is present at birth and does not require imprinting or adaptation to specific antigens. For this reason, it is also referred to as nonspecific immunity. Response to pathogens is rapid, occurring within minutes to hours of exposure. The components of the innate immune system include neutrophils, macrophages, monocytes, dendritic cells, natural killer cells, and the complement system.

Physical, chemical, and biological mechanisms

Cells

The cells involved in innate immunity are listed below. For the specific function of the individual populations see basics of hematology.

Cellular mechanisms

HLA system and pattern recognition receptors

Humoral mechanisms

Humoral mechanisms

The humoral mechanisms of innate immunity is mediated by proteins that are secreted into bodily fluids or the blood stream. These proteins often initiate additional immune responses via:

  • Vasodilation and increasing vascular permeability → increased blood flow
  • Activation, proliferation, and attraction (chemotaxis) of immune cells
  • Killing the pathogen

Acute phase proteins

Complement system

Defects of innate immunity

Immune deficiency Examples of causes

Increased susceptibility to infection for

Granulocyte defect

  • As above
  • Increased numbers of neutrophils in the blood
  • Pus absent
Phagosome defect
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last updated 11/18/2018
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