Monocytes and Macrophages

 

Macrophages are important mediators of the innate immune system and are a key component of acute inflammatory responses to bacteria and other threats.

 

Macrophage Function

Macrophages, along with neutrophils, are phagocytic cells.

Stimulation of macrophages by interferon-gamma, produced by activated T lymphocytes, causes a transformation into angry macrophages, which are more phagocytic and capable of killing intracellular pathogens.

Monocytes develop in the bone marrow and invade tissues as macrophages. Some organs have specialized types of macrohpage, such as the liver's Kupffer cells, the sinus histiocytes in the spleen and lymph nodes, alveolar macrophages, and osteoclasts of the bone.

Tissue macrophage populations can expand by:

• additional recruitment of blood monocytes
• proliferation
• immobilization

 

Angry macrophages are a serious threat to anything that gets in their way.

 

Activation

• Angry macs are stimulated by interferon-gamma, produced by activated CD4+ cells (Th1 subtype), CTLs, or NK cells.

Function

Angry macs are:

• more phagocytic
• more capable of killing intracellular pathogens (such as M. tuberculosis or Legionella) due to increased production of hydrogen peroxide, NO, and lysozymes
• better at presenting antigen due to upregulation of MHC II
• produce more IL-1 and TNF, recruiting more angry macs