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[[Image:LH Macrophage Histology.jpg|thumb|right|125px|<p>'''Macrophage'''</p>^{© Nottingham Uni}]]Macrophages are large, round cells that contain a central round nucleus and have abundant clear, often vacuolated, cytoplasm. Macrophages acts as sentinel cells, have a role in destroying bacteria, protozoa and tumour cells, and release substances that act upon other immune cells. Macrophages are phagocytic, long lived and are found throughout the body.  

[[Image:LH Macrophage Histology.jpg|thumb|right|200px|<p>'''Macrophage'''</p>^{© Nottingham Uni}]]

Macrophages are large, round cells that contain a central round nucleus and have abundant clear, often vacuolated, cytoplasm. Macrophages acts as sentinel cells; they have a role in destroying [[bacteria]], [[protozoa]] and tumour cells, and release substances that act upon other immune cells. They are also responsible for clearing dead and damaged cells and tissue through the process known as efferocytosis. Macrophages are [[Phagocytosis|phagocytic]], long lived and are found throughout the body.

 

==Development==

==Development==

Macrophages are either derived from blood borne [[Monocytes|monocytes]] which have migrated into tissue and differentiated, or from dividing macrophages within the tissue.  

Macrophages are either derived from blood borne [[Monocytes|monocytes]] which have migrated into tissue and differentiated, or from dividing macrophages within the tissue.  

===Locations===

 

==Locations==

<p>Macrophages are present throughout the body with large numbers in the [[Lymph Nodes - Anatomy & Physiology|lymph nodes]], [[Bone Marrow - Anatomy & Physiology|bone marrow]] and [[Spleen - Anatomy & Physiology|spleen]]. In connective tissue macrophages are fixed and referred to as tissue histocytes. Sentinel macrophages in the lung are called alveolar macrophages, while in the [[Liver - Anatomy & Physiology|liver]] they are called Kupffer cells. In the brain they are microglia with long cytoplasmic processes.</p>

<p>Macrophages are present throughout the body with large numbers in the [[Lymph Nodes - Anatomy & Physiology|lymph nodes]], [[Bone Marrow - Anatomy & Physiology|bone marrow]] and [[Spleen - Anatomy & Physiology|spleen]]. In connective tissue macrophages are fixed and referred to as tissue histocytes. Sentinel macrophages in the lung are called alveolar macrophages, while in the [[Liver - Anatomy & Physiology|liver]] they are called Kupffer cells. In the brain they are microglia with long cytoplasmic processes.</p>

===Variations===

==Variations==

====Epithelioid cells====

===Epithelioid cells===

* Look like squamous epithelial cells with a pink (eosinophilic) cytoplasm and indistinct borders.

Epithelioid cells look like squamous epithelial cells with a pink (eosinophilic) cytoplasm and indistinct borders. They may be binucleate and tend to remain in the lesion. It is thought by some people that they may not phagocytose, but instead secrete substances directed against the foreign agent.

* May be binucleate.

 

* Tend to remain in the lesion.

===Giant cells===

* It is thought by some people that they may not phagocytose, but secrete substances directed against the agent.

<p>Macrophages can fuse together to form giant cells (Langhan’s cells), which with their greater cytoplasmic volume and number of lysosomes are able to engulf and deal with large foreign particles/bodies. They are thought to form when two or more macrophages attempt to engulf the same organism; the resulting cell can contain between two to several hundred nuclei per cell).</p><p>The nuclei can be scattered throughout the cytoplasm, clumped in the centre in foreign body granulomas or appear in a horseshoe shape at the periphery of the cytoplasm at one end in [[tuberculosis]] and some other granulomas. In the past, the morphology of these giant cells was correlated with the agent responsible for [[inflammation]], although the distinction is not absolute.</p>

====Giant cells====

<p>Many macrophages may fuse together to form giant cells (Langhan’s cells), which with their greater cytoplasmic volume and number of lysosomes are able to engulf and deal with large foreign particles/bodies. They are thought to form when two or more macrophages attempt to engulf the same organism and are multinucleated (with two to several hundred per cell).</p><p>The nuclei can be scattered throughout the cytoplasm, clumped in the centre in foreign body granulomas or appear in a horseshoe shape at the periphery of the cytoplasm at one end in tuberculosis and some other granulomas. In the past, the morphology of these giant cells was correlated with the agent responsible for inflammation, although the distinction is not absolute.</p>

==Actions==

==Actions==

<p>Macrophages are phagocytic and take up particles and cell debris by endocytosis, as well has engulfing pathogens like bacteria. These are then present in the macrophage inside phagosomes. Lysosomes present in the cytoplasm then bind with the phagosome and release their contents which degrade/digest its contents.</p>

 

<p>Macrophages also act as '''antigen presenting cells''' taking antigens to lymph nodes to present to T cells. MHC II (major histocompatibility complex II) proteins on their surface allow them to interact with helper T cells (CD4). Short peptide segments from foreign cells are presented with MHC II which activates the T cell.</p>

<p>To migrate through connective tissue they release proteases and glycoaminoglycanases.</p>

<p>Macrophages are [[Phagocytosis|phagocytic]] and take up particles and cell debris by endocytosis, as well as engulfing pathogens like bacteria through the specialist function of [[Phagocytosis|phagocytosis]]. These are then present in the macrophage inside phagosomes. Lysosomes present in the cytoplasm then bind with the phagosome and release their contents which degrade/digest its contents. The degradation of the lysosomal contents occurs in much the same way as [[Neutrophils#Actions|neutrophils]] with both oxygen-dependent and oxygen-independent mechanisms.</p>

 

<p>To function correctly macrophages need to correctly identify material that is either foreign (non-self) or which requires removal, such as damaged cells. They are able to recognise some foreign material directly (for example Lipopolysaccharide (LPS)) but in other circumstances proteins (opsonins) that bind to bacteria are required to increase the chances of successfully binding the foreign material to the macrophage. Some examples of opsonins include [[Complement|complement]] component C3bi and bound [[Immunoglobulins|antibody]].  </p>

 

 

<p>Macrophages also act as '''antigen presenting cells''' taking antigens to lymph nodes to present to T cells. MHC II ([[Major Histocompatability Complexes|major histocompatibility complex]] II) proteins on their surface allow them to interact with helper T cells (CD4). Short peptide segments from foreign cells are presented with MHC II which activates the [[T cells|T cell]] as part of the [[Adaptive Immune System|adaptive immune]] response.</p>

 

 

<p>In the latter course of inflammation, it is the blood monocytes, along with [[Dendritic Cells|dendritic cells]] that switch the immune system from innate to adaptive (see above) by interacting with CD4⁺ T helper cells. </p>

 

<p>To migrate through connective tissue they release proteases and glycoaminoglycanases through a process called exocytosis (granule fusion with the plasma membrane).</p>

 

 

===Role in pathology===

===Role in pathology===

<p>Macrophages are seen in both [[Acute Inflammation - Pathology|acute]] and [[Chronic Inflammation - Pathology| chronic inflammation]].</p>  If large numbers of macrophages are found in chronic inflammatory processes, it implies the inability to eliminate the causal organism  e.g. [[Respiratory Bacterial Infections - Pathology#Tuberculosis|Tuberculosis]], [[:Category:Actinobacillus species|''Actinobacilllus'']], fungi, parasites and foreign bodies.

<p>Macrophages are seen in both [[Acute Inflammation|acute]] and [[Chronic Inflammation| chronic inflammation]].</p>  If large numbers of macrophages are found in chronic inflammatory processes, it implies the inability to eliminate the causal organism  e.g. [[:Category:Mycobacterium species|''Mycobacterium'' (TB)]], [[:Category:Actinobacillus species|''Actinobacillus'']], [[fungi]], [[parasites]] and foreign bodies.

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{{Template:Learning

<center><b><sup>Blood cells: [[Erythrocytes|Erythrocytes]] |

|powerpoints = [[Connective Tissue Histology resource|Tutorial about connective tissues, with slides on Macrophages]]

[[Basophils|Basophils]], [[Eosinophils|Eosinophils]], [[Lymphocytes|Lymphocytes]], [[Macrophages|Macrophages]], [[Mast Cells|Mast cells]], [[Monocytes|Monocytes]] & [[Neutrophils|Neutrophils]] |  [[Thrombocytes|Thrombocytes]] & [[Thrombopoiesis - WikiBlood#Megakaryocyte|Megakaryocytes]]</sup></b></center>

 

|date = May 17, 2012}}

 

 

[[Category:Blood_Cells]] [[Category:Robert J Francis reviewed]]