What is an Autoimmune Disease?
White blood cells, with the fancy medical/science term for them being leukocytes, help fight infections, which the science world calls pathogens. However, sometimes some of these cells get a bit mixed up, and can end up actually hurting some of the body’s own cells, aka autoreactive, resulting in autoimmune disease. Some of these white blood cells, called lymphocytes because they can travel around the body’s lymphatic system (think of your lymph nodes!), are able to recognize specific bits/parts of pathogens. This specific portion of what the immune system recognizes is called an antigen. This is really great when we need to fight off a particular infection!
Lymphocytes specific for one antigen are made, but since nothing is perfect, sometimes these lymphocytes can become autoreactive. This actually happens in healthy individuals without autoimmune disease, but in those cases the body is able to delete or control those autoreactive cells, a term called ‘self-tolerance.’
Breakdown of Checkpoints
The immune system has layers of checkpoints that provide a balance between healthy immune function and prevent autoimmunity.
Again,it’s a common occurrence for isolated breakdowns of these checkpoints, even in healthy individuals. Autoimmune disease results only when there are multiple, severe break down of these immune checkpoints, meaning the the resultant amount or function of autoreactive cells has overpowered the self-tolerance mechanisms.
Immune checkpoints that help regulate the body from auto reactivity are described below:
Central tolerance occurs when autoreactive lymphocytes (mainly T cells and B cells) are deleted (aka deletion editing). This deletion process occurs where the cells are matured: T cells in the thymus, and B cells in the bone marrow.
Antigen segregation is a fancy term for physical separation of some component of something that the immune system wants to react to.
Anergy is a fancy science word for exhaustion or inactivity. Basically, a cell is anergic if it’s functionless. So even if a cell is autoreactive, for example trying to react to the body’s own cells, it won’t matter because it can’t do anything!
Regulatory cells are able keep in check the autoreactive cells. They can spit out powerful proteins called cytokines (cell communication molecules) that quiet the autoreactive cells.
Cytokine deviation means switching those cell communication molecules from an inflammatory type that’s driving the inflammation seen in autoimmune disease to a more anti-inflammatory type.
When lymphocytes (remember, T and B cells) see a specific antigen (or something they think they have to react against), they become activated and start spawning LIKE CRAZY. They clone themselves- and like a lot! This process is called clonal expansion. This is great in response to an infection, like the flu, when we want to the immune system to go to war against the virus. And it’s even better, because some of these cells will stick around and REMEMBER those bad flu guys (or whatever the infection is), we call those cells memory cells (crazy, right?). But in autoimmune disease, this is obviously bad to have a whole patroon of immune soldiers against some aspect of the body. So enter clonal exhaustion. This can occur by killing all those clones to that particular antigen once they’ve been activated. Boom, gone.
So you see, the immune system has a lot of checks and balances to make sure that things don’t get too crazy on its everyday mission to defend the body. But, unfortunately, in some people this system of checkpoints can be severely broken down, resulting in autoimmunity.
Of course, it’s not entirely known why autoimmune disease occurs, otherwise there would be a cure or preventative treatment. However, the scientific community has learned a lot, and a basic tenet of autoimmunity comes down to genetics, the environment, and resultant breakdown in immune checkpoints.