Sarcoidosis

With sarcoidosis, sarcoid refers to the flesh and osis means disorder - and the reason that it’s called that, is that sarcoidosis is an immunologic disorder that results in lots of small nodules forming throughout the body.

The disease is poorly understood and is most common among African American females.

Normally, the cells of the immune system are ready to spot and destroy anything foreign pathogens that could cause the body harm.

To help with this, there’s a category of cells in the body called antigen-presenting cells, which include macrophages, B-cells, and dendritic cells.

The most common antigen presenting cells are the dendritic cells which are named after their branch like arms called dendrites.

When an dendritic cell comes in contact with a pathogen, it latches onto it with its dendrites and then engulfs or swallows it.

The pathogen is broken down and the cell presents a piece of it, called an antigen, on a major histocompatibility complex class II molecule, or MHC-class II for short.

Then the dendritic cell 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.

Cytokines are then released by dendritic cell to help activate the helper T-cell and it begins to divide or proliferate.

The new T-cells leave the lymph node and start secreting proinflammatory cytokines, or signaling molecules, that recruit more immune cells like additional T-cells and macrophages.

In sarcoidosis, 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.

The precise trigger isn’t 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.

Sarcoidosis can involve nearly every organ, but they most often involves hilar lymph nodes which are 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 with T cells on the periphery and macrophages in 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.

Oftentimes, macrophages fuse together to form a single large multinucleated cell called a Langhans giant cells.