The Link Between Upper Respiratory Infections and Multiple Sclerosis Relapse
The flu is one of the great fears of winter. Many people worry about how many days of work they’ll miss if they get it, and who will still home with the kids if they get sick. While the flu can be uncomfortable and annoying for most healthy individuals, it can be much scarier for others. Most of us know that the flu can be dangerous for the elderly and people with weak immune systems who may not be able the get the vaccine. This is why getting vaccinated and participating in community immunity is important.
What may not be as well-known is how patients with multiple sclerosis (MS) and other neurological diseases can also have much higher risks associated with getting the flu.
People with MS who get the flu are at risk of having a cascade of immune responses triggered that can cause them to fully relapse also known as an acute attack. These relapses are defined as episodes that encompass a focal neurologic disturbance that is preceded by a period of overall instability that has lasted 30 days or more. New research shows how MS patients can go into relapse due to acquiring an upper respiratory infection.
The research
A recent study from the University of Illinois looks at what happens in the brain when MS patients have an upper respiratory infection. Andrew Steelman, an assistant professor appointed in the Department of Animal Sciences, the Neuroscience Program, and the Division of Nutritional Sciences at the University of Illinois, says that while “We know that when MS patients get upper respiratory infections, they're at risk for relapse, but how that happens is not completely understood. A huge question is what causes relapse, and why immune cells all of a sudden want to go to the brain. Why don't they go to the toe?" This question prompted the team to do some research that might shed some light on the pathophysiology that causes the relapse.
They looked at mice that were exposed to and contracted the flu and then they thoroughly examined their bodies, including the brain. These mice were already genetically prone to having an autoimmune attack on their brain and spinal cord. This means that the immune system of the mice attacked their own body. This is very similar to how the immune system of patients with MS attacks and damages the nerve cells and their connections with the brain and spinal cord.
The researchers found that mice infected with the flu did exhibit MS-like symptoms even though they did not find the flu virus in the brain. Steelman also explained that if you look at MS patients who are infected with the flu, you will see that about 27 to 42 percent will relapse within the first few weeks. This is the same incidence and time frame that was found in the University of Illinois mice study. Researchers actually expected the incidence in the mice to be higher since their immune cells are able to attack the brain.
Looking at the brains of the infected mice showed an increase in glial activation. Glia cells are a type of supportive cell in the central nervous system (CNS). They do not conduct electrical impulses like nerve cells, but instead they offer support and insulation between the nerve cells. These supportive functions help nerve cells maintain their ability to conduct electrical impulse between one another. Glia cells are much more abundant than nerve cells in the brain and there are a few different types. They are also responsible for modulating the rate of nerve signals. Additionally, some types of glia recruit immune cells to the brain. Researchers think that this may be one way in which the glial activation from the flu infection can increase relapse potential. In MS patients, the recruited immune cells attack the myelin sheath of the nerve cells when they get to the brain. The destruction of the myelin sheath results in neurologic dysfunction. But how do the glia cells recruit the immune cells in the first place?
The cells and parts of the body have many methods for communicating with one another. There are various signaling molecules that can send messages from one cell type to another. Researchers at the University of Illinois believe that glia cells may signal the immune cells using molecules called chemokines. During their research they found that the level of one particular chemokine (CXCL5) was elevated in the brains of the mice that had been infected with the flu virus. This same chemokine was also elevated and found in the spinal fluid of MS patients that had relapsed. In addition, another research group has suggested that this chemokine can be used to predict relapse in MS patients.
Now what?
There is still a lot that needs to be researched regarding why the immune system attacks the brain. This is still poorly understood, and having more knowledge about this phenomenon will enhance researcher’s ability to identify effective treatments and potential cures. Knowing more about how immune cells are recruited to the brain during an upper respiratory infection can be helpful in preventing relapses, and identifying potential drugs in the future. MS relapses are thought to contribute to overall progression of the disease. If these relapses can be prevented and managed better when they do occur, the overall life expectancy of MS patients could increase. Early intervention with appropriate medications to manage upper respiratory infections could slow or limit relapses. Steelman from the University of Illinois says that “If we could inhibit relapse by 50 percent, we could theoretically prolong the time it takes for the patient to experience continual loss of function and dramatic disability.”
This study has provided valuable information. It would be great to see them move forward with more animal studies that perhaps aim to halt the signaling of the immune cells. Ideally this would prevent the immune cells from coming to the brain of individuals with upper respiratory infections, and thus help prevent relapses. Additionally, patients with MS should strongly consider getting the flu vaccine. Despite numerous rumors floating around on the internet, the flu vaccine does not give you the flu. People who report getting sick after vaccination, were likely already infected a couple days before receiving the vaccine. The Academy of Neurology, in collaboration with the Immunization Panel of the Multiple Sclerosis Council for Clinical Practice Guidelines, has provided evidence that is designed to help MS patients and providers decide which vaccines to receive in order to best prevent illness related relapses. While this includes some guidance on deferring vaccinations if the patient is currently experiencing a relapse, the overall concensus is that MS patients should receive the seasonal inactivated flu shot, and that this is safe for this population. MS patients should avoid the nasal spray vaccination since this is a live virus and could pose some risks to the patient. Though the effectiveness of the flu vaccine varies a bit every year, it is one of the best ways for MS patients to prevent themselves from getting infected with the flu, and the subsequent relapses that can occur.
