Difference between revisions of "Category:Innate Immune System"

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==Cellular responses==
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==[[Innate Immunity Cellular Responses]]==
[[Image:LH Macrophage Histology.jpg|thumb|right|125px|<p>'''Macrophage'''</p><sup>© Nottingham Uni</sup>]]
 
* If pathogens breach the barriers formed by the skin and mucus membranes, they must be detected and destroyed by cellular and humoral means
 
* The cells involved with innate protection are:
 
** Blood granulocytes, or Polymorphonuclear Cells
 
*** Notable for their multi-lobed nuclei
 
*** '''Neutrophils''': phagocytose bacteria
 
*** '''Eosinophils''': kill parasites by the release of granules
 
*** '''Basophils/ mast cells''': kill parasites by the release of granules
 
** Blood '''[[[[Monocytes|monocytes]]]]''': phagocytose bacteria
 
** Tissue mast cells and '''macrophages''': phagocytose bacteria
 
*Effectively, innate cellular response seeks to hold off the infection until the [[Adaptive Immune System - WikiBlood|adaptive]] response can back it up with a more specific attack
 
 
 
 
 
===[[Macrophages|Macrophages]]===
 
[[Image:Monocytes.jpg|thumb|right|150px|Monocytes - J. Bredl, RVC 2008]]
 
*The role of macrophages in Innate Immunity is to act as primary '''phagocytes'''
 
* Macrophages are present within tissues and take the form of distinct, tissue-specific populations:
 
** Alveolar macrophages
 
** Tissue histiocytes
 
** Glomerular macrophages
 
** Hepatic Küpffer cells
 
** CNS microglia
 
** Sinus-lining macrophages of the lymph nodes and spleen
 
* [[Monocytes|'''Monocytes''']] (immature macrophages) are circulating phagocytes
 
** Circulate for 6-8 hours
 
** Can function as phagocytes within the blood and as newly migrated cells in tissues
 
** Chiefly function to replace the various tissue macrophage populations
 
 
 
===[[Neutrophils|Neutrophils]]===
 
[[Image:Neutrophil 2.jpg|thumb|right|150px|Neutrophils - J. Bredl, RVC 2008]]
 
* Neutrophils are the principal, highly active '''phagocytes''' in the blood
 
** Comprise 30-70% of white blood cells depending on species
 
** Kill and digest microbes in a similar way as macrophages
 
* Neutrophils can also cause extracellular bacterial killing by disrupting bacterial membranes
 
** Secrete small antibacterial peptides
 
*** E.g. defensins and bactenecins
 
* Neutrophils produce vasoactive peptides
 
** E.g. histamine and bradykinin
 
** Cause a great increase in extravasation of blood granulocytes and [[Monocytes|monocytes]] and plasma proteins at the site of infection
 
* Neutrophils are the archetypal cell associated with [[Inflammation - WikiBlood|acute inflammation]]
 
** Are attracted to sites of inflammation by:
 
*** Complement activation
 
*** Cytokine production
 
*** Changes to vascular endothelium
 
** Neutrophil activation in an inflammatory lesion results in the release of '''prostaglandins'''
 
*** Responsible for vasoactive changes and for pain
 
* The accumulation of dead and dying [[Neutrophils|neutrophils]] at the site of infection is called '''pus'''
 
** Their removal from the site after the removal of infection is an important step in the resolution of the lesion
 
 
 
===[[Eosinophils|Eosinophils]]===
 
[[Image:Eosinophil.jpg|thumb|right|150px|Eosinophil - J. Bredl, RVC 2008]]
 
* Eosinophils are less common than [[Neutrophils|neutrophils]], and they are not phagocytic
 
** Make up <5% of the leukocytes in normal blood
 
* Eosinophil numbers are increased:
 
** Slightly during the resolution phase of inflammation
 
** Many-fold in parasite-infected animals
 
*** The presence of a large proportion of eosinophils in a blood smear is highly indicative of parasitaemia
 
* Mainly function by targeting the surface of parasites by means of specific antibody or complement
 
** Release a large range of toxic molecules that break down the parasite integument
 
* Prominent in [[:Category:Allergic Diseases|allergic]] (anaphylactic) reactions
 
 
 
===[[Basophils|Basophils]] / [[Mast Cells|Mast Cells]]===
 
[[Image:Basophil and Lymphocyte.jpg|thumb|right|150px|Basophil - J. Bredl, RVC 2008]]
 
* Basophils/mast cells are principally localised at epithelial surfaces
 
** Very small numbers are present in blood
 
*** Less than 0.5% circulating leukocytes
 
* They have two principal functions:
 
*# Induction of [[Inflammation - WikiBlood|acute inflammation]]
 
*#* Trauma and/ or bacterial infection causes the production of '''cytokines''' by the mast cells that induce a classical acute inflammatory response
 
*# Response to parasite infection
 
*#* Specific [[Immunoglobulins|IgE]] binds cells
 
*#* Subsequent contact with antigen causes the mast cells to degranulate
 
*#* Release enzymes and vasoactive substances that can result in a high level of mucus secretion and smooth muscle contraction
 
* Also produce factors that influence local host cell physiology
 
** Various mediators increase the ratio of phagocyte to microbe
 
  
 
=Innate Immunity to Viruses=
 
=Innate Immunity to Viruses=

Revision as of 15:56, 13 August 2010

Introduction

The Innate immune system is the body's first barrier of defence to infection. It relies on an older, more generic, and faster acting set of tools than the adaptive system. While the adaptive system is essential for a specific response to infection, it is ultimately the innate system that conquers foreign attackers through means of phagocytosis.

  • Non-specific protective mechanisms include such innate factors as:
    • Physical barriers
      • Skin
      • Ciliated mucous membranes
      • Commensal organisms
    • Humoral factors
    • Cellular mechanisms
      • Phagocytosis
    • Factors which regulate species specificity
      • Membrane receptors for pathogens
      • Nutritional requirements
      • Temperature
      • pH
  • Mechanisms of innate immunity are always present and generally unchanging
  • Adaptive immunity is acquired only on contact with the infectious agent (antigen) and therefore does not function before first contact with the antigen

Actions of the Innate Immune System

Recognition of Microorganisms

Phagocytosis

Tools of Innate Immunity

Innate Immunity Barriers

Humoral Factors of Innate Immune System

Innate Immunity Cellular Responses

Innate Immunity to Viruses

Innate response to dsRNA - B. Catchpole, RVC 2008

Because viruses invade host cells to take over a host's cellular machinery, the innate system has a more difficult time detecting viruses as foreign agents. However, there is a give-away element of the viral attack that the innate system can recognize: the double-stranded RNA (dsRNA) produced by a virus in its replication phase. Because mammalian cells only ever produce single-stranded RNA, the presence of dsRNA signals a foreign intruder. dsRNA can be detected by TLR-3R on the cell surface or intracellularly by the presence of dsRNA-dependent protein kinase.


The innate response to viral attack also depends on the presence of Type-1 Interferons, which are produced by all cells on recognition of a viral attack. Interferons serve to increase degradation of mRNA, inhibit protein synthesis, and increase the effectiveness of the adaptive response by increasing antigen presentation to antibody.


Lastly, the final line of defense for the innate response to viruses lies in the actions of Natural Killer (NK) cells. These warriors monitor the production of MHC (Major Histocompatibility Complex) on the surface of cells, which is produced as part of the adaptive response. A cell whose cellular machinery is compromised by viral infection will experience a drop in the amount of MHC it produces. When a cell's MHC production drops, NK cells are triggered to phagocytose these cells. As such, this is a non-specific targeting based simply on the ability of a cell to function normally, which also lends them to playing a role in targeting malignant cells. NK cells are incapable of directly targeting viral infection.

Innate Immunity to Bacteria

Bacterial responses - B. Catchpole, RVC 2008

The innate response to bacterial infection lies in its first-response role of detection of a foreign organism. By using the above described tools of Pattern-Recognition Receptors (PRRs), the innate response flags up problems while the adaptive response gets itself organized. Once a foreign organism is detected, the innate system responds by engaging in cell warfare via phagocytosis and triggering the inflammatory response. The release of inflammatory cytokines will cause an increase in vasodilation, vascular permeability and an influx of white blood cells. Neutrophils take on their primary role as phagocytes in this phase. In addition, systemic effects of inflammatory cytokines will sustain a rise in core temperature (fever), the release of acute phase proteins from the liver, and bone marrow mobilization as the need for white blood cells production is increased. Acute phase proteins will bind to bacterial cell walls, enhancing neutrophil, macrophage, and complement-initiated phagocytosis.

Interplay of Innate and Adaptive Immunity

Innate Immunity Flashcards

Links

Websites

References