Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease where the immune system mistakenly attacks its own healthy tissues and organs. This systemic inflammation can affect nearly any part of the body, including joints, skin, kidneys, and blood cells. White Blood Cells (WBCs), also known as leukocytes, are a major component of the immune system, defending the body against foreign invaders like bacteria and viruses. Because SLE directly targets immune components, the disease frequently causes significant changes in the total number and composition of these circulating white blood cells.
Lupus’s Typical Impact on White Blood Cells (Leukopenia)
Despite the question focusing on a high count, the most common finding in individuals with active SLE is actually a low total WBC count, a condition medically termed leukopenia. This reduction in circulating cells is a reflection of the systemic autoimmune attack characteristic of the disease. The primary mechanism involves the production of autoantibodies, which are misguided proteins that target and destroy white blood cells.
Autoantibodies bind to the surface of circulating leukocytes, marking them for destruction by scavenger cells in the spleen and liver. This leads to the premature removal and breakdown of white blood cells from the bloodstream. Furthermore, chronic inflammation and SLE activity can suppress the bone marrow, which produces new blood cells. This suppression reduces the output of leukocytes, compounding the problem of peripheral cell destruction.
Leukopenia is observed in almost half of SLE patients and is recognized as one of the classification criteria for the disease. This low count is often an indicator of active disease, meaning the lupus is currently flaring or causing systemic damage. The decrease in total WBCs is not always even across all cell types, but the most frequently affected cell line is the lymphocytes.
The Importance of the Differential White Blood Cell Count
The total white blood cell count provides only a single number, which is insufficient for understanding the immune status of an individual with lupus. A more informative measure is the differential count, which breaks down the total count into the five major subtypes of leukocytes: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Each of these subtypes plays a distinct role in immunity, and their individual counts can signal different processes at work.
For instance, a low count of lymphocytes, or lymphopenia, is one of the most frequent abnormalities observed in active SLE. This occurs because the lupus autoantibodies are particularly aggressive toward these cells, which are central to the autoimmune response. Because of this specificity, lymphopenia is often a strong indicator of active disease, even if the total WBC count remains in the low-normal range.
Neutrophils, the most abundant type of white blood cell, may also be low (neutropenia) due to autoantibody destruction or bone marrow suppression. However, in some cases of active SLE, the neutrophil count may be high, a condition known as neutrophilia. This rise can be due to systemic inflammation preventing the body from properly clearing the neutrophils, leading to their accumulation. Analyzing these individual counts is essential, as the pattern of cell changes helps distinguish between disease activity, medication effects, or secondary infections.
Explaining High White Blood Cell Counts in Lupus Patients
While leukopenia is the typical presentation of active SLE, a high total white blood cell count (leukocytosis) can occur in lupus patients, signaling an important change in their condition. The most significant cause for a sudden rise in the WBC count is the presence of an infection, particularly bacterial infections. Since the patient’s immune system is often compromised by autoimmune activity and immunosuppressive treatment, a high WBC count must be treated as a serious red flag for potential infection.
The second major cause of leukocytosis is the use of glucocorticoids (steroids), a routine treatment for managing lupus flares. Steroids cause a non-infectious rise in the total WBC count, primarily by increasing the number of circulating neutrophils. The drug achieves this effect through a process called demargination, where neutrophils temporarily stuck to blood vessel walls are released back into circulation.
Steroids also delay the normal process of programmed cell death (apoptosis) for neutrophils and slow their migration out of the bloodstream into tissues. These combined effects result in more neutrophils remaining in the circulation, often increasing the count by around 4,000 cells/mm³. This pharmaceutical effect must be carefully differentiated from an infection. Steroid-induced leukocytosis typically lacks the specific signs of a bacterial infection, such as a high number of immature neutrophils or a corresponding fever.