Macrophages

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Immunology

Summary

There are two types of macrophages: monocyte-derived and non-monocyte-derived. Monocyte-derived macrophages can be distinguished by their CD14 cell surface marker, while non-monocyte-derived macrophages are derived from embryological structures. Monocyte-derived macrophages circulate as monocytes in the blood and transform into macrophages once they've arrived in the tissue. This is in contrast to non-monocyte-derived macrophages, which arise and remain in tissues. Regardless of their origin, in tissue, macrophages phagocytose cells targeted for destruction and clean up cellular debris. When activated by interferon gamma, secreted by helper T-cells and natural killer cells, macrophages express more MHC class two molecules and increase their antigen presenting capabilities. By secreting TNF alpha, macrophages may recruit other immune cells to the site of an infection. Activated macrophages can also increase production of reactive oxygen species, like hydrogen peroxide and nitric oxide. Finally, macrophages promote healing of damaged tissues by aiding in new blood vessel growth and laying down a collagen-rich extracellular matrix causing fibrosis.

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FAQs

What are the different classes of antibodies and their respective functions?

There are five classes of antibodies; IgM, IgG, IgA, IgE, and IgD. IgM is the first antibody produced in response to an infection. IgG is involved in long-term immunity, crossing the placenta to provide immunity to the fetus. IgA protects mucosal surfaces like the nose, breathing passages, digestive tract, and ears. IgE is involved in allergy and responses to parasites. IgD role is still not completely known but it is mainly found on the surface of B cells as a receptor.

What role do Activated Naive B Cells play in the formation of antibodies?

Activated naive B cells play a central role in the production of antibodies. Upon encountering an antigen, naive B cells are activated and differentiate into plasma cells, which produce antibodies specific to that antigen. Besides, some of the activated naive B cells develop into memory B cells that can quickly respond to future exposure to the same antigen.

What is the function of the IgM antibody in the immune system?

IgM is the first antibody to be produced during a primary immune response to an antigen. It has a pentameric structure that allows it to effectively bind and agglutinate pathogens. IgM is very effective at complement activation, helping to lead to the destruction of the pathogens.

How does the IgA antibody contribute to mucosal immunity?

IgA antibodies are chiefly responsible for mucosal immunity. They are produced by plasma cells in the mucosal lining and function to neutralize pathogens in the mucosal surfaces of the body like the respiratory, gastrointestinal, and urogenital tracts, thus preventing their entry into the body.

What is antibody-dependent cellular cytotoxicity and how does it work?

Antibody-dependent cellular cytotoxicity (ADCC) is a mechanism of immune defense whereby an effector cell of the immune system actively lyses a target cell, whose membrane-surface antigens have been bound by specific antibodies. It is one of the mechanisms through which antibodies, as part of the humoral immune response, can limit and contain infection.

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