Neutrophils Fail Quietly in Multiple Myeloma Even When Counts Look Normal

Neutrophils are the immune system’s first responders, flooding sites of infection within minutes and destroying bacteria with a combination of engulfment and chemical warfare. In patients with multiple myeloma, an incurable cancer of antibody-producing plasma cells, these frontline defenders have long been suspected of underperforming, but the evidence has been fragmentary and often limited to counting how many neutrophils circulate in the blood. A new study from Zambia now provides some of the most direct functional evidence yet that the problem is not how many neutrophils patients have, but how poorly the ones they have actually work.

The research, conducted at the University Teaching Hospital and the Cancer Diseases Hospital in Lusaka, recruited 30 patients with multiple myeloma and 42 age- and sex-matched healthy controls. The investigators, led by Kapina Mwampembwa and colleagues, designed the study as a cross-sectional analytical comparison, meaning they measured neutrophil function at a single point in time across both groups and then examined how strongly the measurements discriminated between patients and controls. Crucially, the cohort included both newly diagnosed and relapsed patients, allowing the team to capture immune dysfunction across the disease course rather than in a single, potentially unrepresentative stage.

Multiple myeloma arises when plasma cells, the antibody factories of the bone marrow, proliferate uncontrollably and crowd out healthy blood-forming tissue. The disease is already known to suppress immunity in several ways: malignant plasma cells displace normal immune precursors, produce abnormal antibodies that fail to neutralize pathogens, and alter the bone marrow microenvironment in ways that impair immune cell development. Infections remain one of the leading causes of illness and death in myeloma patients, particularly during early treatment when disease-related immune suppression overlaps with the effects of chemotherapy. Whether neutrophils themselves contribute meaningfully to this infection risk has been difficult to establish, because standard blood counts often appear reassuringly normal.

To test neutrophil function directly, the researchers drew four milliliters of venous blood from each participant into tubes containing EDTA, an anticoagulant that preserves cells for laboratory analysis. Neutrophils were then isolated from the whole blood using a density-gradient medium called Polymorphprep, which separates blood cells into distinct layers based on their density, allowing a purified neutrophil fraction to be collected. This step is critical because functional assays are only interpretable if the cells being tested are a well-defined population rather than a mixture of different white blood cells.

The team then ran two complementary assays, both read by flow cytometry, a technique that passes individual cells through a laser and measures fluorescent signals emitted by each one. The first test measured phagocytosis, the process by which neutrophils engulf bacteria. Researchers incubated the isolated neutrophils with fluorescently labeled bacterial particles and used the flow cytometer to determine what proportion of neutrophils had successfully swallowed the particles, indicated by fluorescence inside the cells. The second test measured the oxidative burst, the explosive production of reactive oxygen species that neutrophils deploy to kill the microbes they have engulfed. For this, the cells were loaded with a fluorescent probe, 2′,7′-dichlorodihydrofluorescein diacetate, which becomes fluorescent when oxidized by the reactive chemicals generated during the respiratory burst. A brighter signal means more active bacterial killing machinery.

The results were striking. Neutrophils from myeloma patients engulfed bacterial particles at a rate of 45.0 percent on average, compared with 75.9 percent in healthy controls, a difference that was highly statistically significant with a P value below 0.001. Oxidative burst showed a nearly identical pattern: only 44.7 percent of patient neutrophils produced reactive oxygen species at detectable levels, versus 74.9 percent of control neutrophils, again with P below 0.001. In practical terms, roughly half of the functional capacity of these innate immune cells was missing in the patient group, even though many of these patients had absolute neutrophil counts within the range that clinicians would normally consider adequate.

To quantify how strongly these functional defects were tied to myeloma itself, the researchers turned to logistic regression, a statistical method that estimates the odds of an outcome, in this case being a myeloma patient, as a function of one or more predictor variables. The associations were extraordinary in magnitude. Patients with impaired oxidative burst had odds of being in the myeloma group more than five thousand times higher than those with normal burst activity, with an odds ratio of 5097.6 and P below 0.001. Phagocytic dysfunction produced an even larger odds ratio of 7272.7, also highly significant. These figures should be interpreted with caution, because odds ratios of this size in a modestly sized cross-sectional study reflect near-perfect separation between groups rather than a literal risk multiplier, but they underscore just how consistently the functional defects tracked with the disease.

Equally informative was what did not predict dysfunction. Age, sex, total white blood cell count, and absolute neutrophil count all failed to show significant associations with either phagocytic capacity or oxidative burst in the regression models. This finding cuts against the conventional reliance on the absolute neutrophil count as the primary marker of innate immune competence in cancer patients. A patient whose blood report shows a normal neutrophil number may nonetheless harbor neutrophils that are functionally crippled, unable to engulf bacteria or generate the reactive chemicals needed to kill them. The study’s authors argue that this qualitative impairment, invisible on routine full blood counts, may help explain why myeloma patients suffer serious infections even when they are not classically neutropenic.

The mechanisms behind the dysfunction remain to be fully worked out, but several plausible candidates follow from myeloma biology. Malignant plasma cells secrete cytokines and other signaling molecules that can suppress myeloid cell development in the bone marrow, potentially releasing neutrophils that are immature or intrinsically defective. The abnormal antibodies produced by the tumor can form immune complexes that pre-activate or exhaust neutrophils in the circulation. In addition, the chronic inflammatory state that accompanies advanced cancer is known to generate a population of suppressive, functionally impaired granulocytes in both human cancers and animal models. The current study did not dissect these pathways, but by demonstrating that the defect is real, reproducible, and measurable with standard flow cytometry tools, it establishes the foundation for such mechanistic work.

The clinical implications are potentially significant. If neutrophil dysfunction can be monitored over time, clinicians might identify patients at heightened infection risk before an infection occurs, guiding decisions about prophylactic antibiotics, immunoglobulin replacement, or the intensity of chemotherapy regimens. Functional assays of the kind used here require only a small blood sample, a density gradient, and a flow cytometer, making them feasible in regional hospitals in high-burden settings, although they are more technically demanding than a routine blood count. The study also carries broader relevance beyond myeloma, since qualitative neutrophil defects are increasingly recognized in other hematologic malignancies and in critically ill patients. For now, the message from Lusaka is clear: in multiple myeloma, the immune system’s most abundant soldiers may be present in full number yet fighting at half strength, and only by testing what they can do, rather than how many there are, can that hidden vulnerability be seen.

Subject of Research: Neutrophil functional impairment in patients with multiple myeloma

Article Title: Functional characterization of neutrophils in patients with multiple myeloma

Article References: Mwampembwa, K., Mweni, E., Mwape, H., Daka, R., Nzobokela, J., Chisanga, C., & Munsaka, S. (2026). Functional characterization of neutrophils in patients with multiple myeloma. PLOS One, 21(10), e0360063. https://doi.org/10.1371/journal.pone.0360063

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0360063

Keywords: multiple myeloma, neutrophils, phagocytosis, reactive oxygen species, flow cytometry, innate immunity, immune dysfunction, infection risk, logistic regression, Zambia, hematologic cancer, plasma cells