With sarcoidosis, sarcoid refers to the flesh and osis means disorder - and the reason we called it that, is that sarcoidosis is an immunologic disorder that results in lots of small nodules forming throughout the body. The disease is actually poorly understood though we know it’s most common among African American females.
Normally, the trusty cells of the immune system are ready to spot and destroy any foreign pathogens that could cause the body harm. To help with this mission, there’s a category of cells in the body called antigen-presenting cells, and these include macrophages, B-cells, and dendritic cells.
The most common member of the antigen presenting cell club is the dendritic cell which is named after its long beautiful branch-like arms called dendrites. When a dendritic cell comes into contact with a pathogen, it latches onto it and with its dendrites pulls and engulfs it. The pathogen is then broken down and the dendritic cell presents a piece of it, called an antigen, on something called a major histocompatibility complex class II molecule, or MHC-class II for short.
The dendritic cell then carries the antigen to the lymph node to find some naive helper T-cells which are T-cells that have never seen an antigen before. Eventually, it runs into a naive helper T-cell with a T-cell receptor that recognizes and binds to the antigen. Then, Cytokines get released by the dendritic cell and this helps to activate the helper T-cell which then begins to divide or proliferate.
The new T-cells then leave the comfort of their lymph node to fulfill their destiny in the great fight against infection. These brave T-cells start secreting proinflammatory cytokines, or signaling molecules, and they then recruit more immune cells like additional T-cells and macrophages.
In sarcoidosis though, this process unfolds over and over throughout the body without the presence of a specific pathogen that the body is trying to destroy. In other words, the immune system seems to be going a bit haywire in the absence of a pathogen. Now, the precise trigger isn’t actually known, but there are some known genetic and environmental risk factors.
Genetic risk factors include being African American and having a family member with sarcoidosis. Environmental risk factors include a prior infection with Mycobacterium tuberculosis and Borrelia burgdorferi, but to be specific, these pathogens are long gone when the autoimmune problem sets in.
So when sarcoidosis is triggered, T cells and macrophages get attracted to a particular spot of healthy tissue. Now, Sarcoidosis can involve nearly every organ, but they most often involve hilar lymph nodes which are the lymph nodes that are near the point where the bronchi meets the lung.
As more and more immune cells gather at a particular spot, they form small nodules called granulomas. These granulomas have T cells on the periphery and macrophages at the center. The granulomas in sarcoidosis are noncaseating which means that there is no tissue necrosis at the center of the granuloma, unlike some other granulomatous diseases like tuberculosis.