Multiple Sclerosis (MS) is a chronic inflammatory condition targeting the central nervous system (CNS), specifically the brain and spinal cord. It is characterized by the immune system mistakenly attacking the myelin sheath, the protective layer around nerve fibers. White blood cells (WBCs), also known as leukocytes, are the body’s immune defenders. Their total count is routinely measured in a Complete Blood Count (CBC) to assess systemic health and inflammation. The relationship between MS and WBC count is complex, involving both localized CNS inflammation and the systemic circulation.
Total White Blood Cell Count and MS
Multiple Sclerosis is an autoimmune disease where inflammation is largely confined to the CNS, which is shielded by the blood-brain barrier. In a stable disease course, the total peripheral WBC count measured in a standard blood test often falls within the normal reference range. However, studies comparing MS patients to healthy individuals show that the total WBC count can be statistically higher, particularly at the time of diagnosis or during an acute relapse.
This elevation is generally not a massive increase but is driven by specific components of the innate immune system. Neutrophils, monocytes, and basophils, which are involved in the initial inflammatory response, have been observed in higher numbers in MS patients compared to controls. This subtle shift suggests a background of systemic immune activation, even if the total count remains within the normal spectrum. Conversely, the WBC count in the cerebrospinal fluid (CSF) of MS patients is usually low, which helps physicians rule out active infection or other conditions causing a high CSF leukocyte count.
The Role of Specific Immune Cells in MS Pathology
While the total WBC count in the peripheral blood may be close to normal, the types of white blood cells and their behavior are central to MS pathology. Lymphocytes, including T-cells and B-cells, are the primary drivers of the autoimmune attack on the CNS. These cells are activated in the peripheral lymphoid organs before migrating into the brain and spinal cord.
Pathogenic T-cells, such as T helper 1 (Th1) and T helper 17 (Th17) cells, recognize and attack myelin components. They cross the blood-brain barrier (BBB) by binding to adhesion molecules on the vessel walls to gain entry into the CNS. Once inside, these T-cells release pro-inflammatory signaling molecules that promote local inflammation and recruit other immune cells.
B-cells also play a significant role, extending beyond antibody production. They act as antigen-presenting cells, activating T-cells and sustaining the autoimmune response within the CNS. The presence of B-cells and their plasma cell derivatives in the meninges leads to the production of abnormal antibodies, known as oligoclonal bands, found in the CSF. The combined action of these T-cell and B-cell subsets drives the demyelination and subsequent nerve damage characteristic of MS.
Factors That Can Elevate WBC in MS Patients
An elevated total WBC count in an MS patient is usually a sign of a co-occurring issue rather than the disease itself. Infections are the most common cause, particularly urinary tract or respiratory infections, which can be more prevalent in people with mobility issues. The standard response to an infection is to significantly increase the production and circulation of neutrophils, leading to a transient rise in the total WBC count.
The use of high-dose corticosteroids, such as methylprednisolone, to treat an acute relapse is another common cause of temporary WBC elevation, known as leukocytosis. This is a physiological effect of the medication, not a sign of infection. Corticosteroids cause neutrophils to “demarginate,” meaning they detach from blood vessel walls and enter the circulation, which artificially inflates the count.
This steroid-induced leukocytosis is compounded by the drug’s ability to inhibit the migration of neutrophils into tissues and delay their natural cell death, prolonging their presence in the bloodstream. This effect is predictable, peaking hours after administration and resolving days to weeks after the treatment is stopped. Some Disease Modifying Therapies (DMTs) can also affect WBC counts, though many are designed to lower specific lymphocyte counts to reduce inflammation.