Multiple Sclerosis & Molecular Mimicry

Environmental factors in MS – Infection

We know that there is an environmental component to multiple sclerosis.  We know that there is an immune component to multiple sclerosis.  One common way of linking these two factors is by suggesting that an infection (bacterial or viral) may play a role.  Indeed, a lot of research has been done in this area and has suggested potential links with infectious agents such as Epstein-Barr virus (EBV, responsible for glandular fever) and Chlamydophila pneumoniae (bacteria that causes pneumonia).  Whilst no conclusive association has been determined, the question remains that if a link did exist, how would that result in MS?  There are many potential theories about this as well, but today we are just going to explain one of them….molecular mimicry.

What is molecular mimicry?

Imagine for a second that you are detective hunting a dangerous criminal.  All that you have to go on is a photo that was taken at the last crime scene.  Sounds simple enough right?  Walk the streets and check surveillance footage until you see them…you make the arrest and take the suspect in for questioning.

It was all going smoothly until they claim that they aren’t the person that you are looking for, they are in fact, the identical twin of the criminal.  Do you believe them?  Probably not…you lock them away, job done (although poorly)!

Now imagine that same scenario occurring in your body, but instead of a dangerous criminal, let’s imagine a virus or a bacteria (or more accurately, a specific part of that virus or bacteria).  Instead of a detective, you have immune cells that are designed to recognise this foreign organism and destroy it.  Instead of an identical twin, the part of the virus or bacteria looks exactly the same as part of a protein that makes up the myelin sheath.

What happens next?  Well in the same way that the detective apprehended the wrong twin, the immune system recognises ‘self’ instead of ‘foreign’.  This concept of having cells of the immune system that are specific for foreign organisms, but also react against our own tissues is what we know as ‘molecular mimicry’.

What does this mean?

The reality for MS is that the concept isn’t quite as simple as described here.  More likely, the identical twin would need to be observed under very specific conditions to be apprehended (e.g. certain lighting, from a certain angle, wearing certain clothes etc).

In the same way, we know that if infection does play a role in MS, it most likely isn’t a direct cause (as many of the suggested infections don’t lead to MS in 100% of cases).  That tells us that it would be the result of an infection with a combination of other environmental and genetic factors.

If molecular mimicry was found to play a part in MS, it would open the door for a new range of treatments.  Could we try and vaccinate to prevent the infection happening in the first place?  Could we try and stop the immune cells reacting against that specific target to prevent the autoimmune response? There are many possibilities, but we haven’t yet worked out if it is in fact involved.  Until then, hopefully this at least helps explain what is meant when you hear the term ‘molecular mimicry’.