Age- and Sex-Matched Normal Leukocyte Subset Ranges in the General Population Defined with the EuroFlow Lymphocyte Screening Tube (LST) for Monoclonal B-Cell Lymphocytosis (MBL) vs. Non-MBL Subjects

Simple Summary Assessment of the status of the immune system in both health and disease requires robust and reliable reference ranges for the different blood leukocyte (sub)populations that take into consideration factors that might influence their distribution, such as age, sex, ethnicity and the presence vs. absence of low-count monoclonal B-cell lymphocytosis with a chronic-lymphocytic-leukemia-like phenotype (MBLlo). It should be noted that despite MBLlo being highly prevalent in the general population and being associated with immune impairment, MBLlo individuals have not been previously excluded in the definition of normal leukocyte ranges. Here, we provide reference cell-count ranges for the major leukocyte populations identified in blood using an optimized and fully validated 8-color flow-cytometry antibody combination based on the largest (n = 706) cohort reported to date of Caucasian adult donors from the general population, grouped by age and sex, and highlight the altered immune profiles associated with MBLlo (622 non-MBL and 84 MBLlo subjects). Reference ranges of blood-circulating leukocyte populations by, e.g., age and sex, are required for monitoring immune-cell kinetics. Most previous reports in which flow cytometry has been used to define the reference ranges for leukocyte counts included a limited number of donors and/or cell populations and/or did not consider age and sex simultaneously. Moreover, other factors not previously considered in the definition of normal ranges, such as the presence of chronic-lymphocytic-leukemia (CLL)-like low-count monoclonal B-cell lymphocytosis (MBLlo), might also be associated with an altered distribution of leukocytes in blood in association with an immunodeficiency and increased risk of infection and cancer. Here, we established reference cell-count ranges for the major populations of leukocytes in blood of non-MBL and MBLlo adult Caucasians matched by age and sex using the EuroFlow Lymphocyte Screening Tube (LST). A total of 706 Caucasian adult donors-622 non-MBL and 84 MBLlo-were recruited from the general population. Among non-MBL donors, the total leukocyte, neutrophil, basophil dendritic cell and monocyte counts remained stable through adulthood, while the absolute numbers of T- and B-cell populations and plasma cells decreased with age. The number of eosinophils and NK-cell increased over time, with clear differences according to sex for certain age ranges. In MBLlo subjects, few differences in the absolute cell counts by age (vs. non-MBL) were observed, and MBLlo men and women showed similar trends to non-MBL subjects except for the B-cell count drop observed in >70 y-men, which was more pronounced in MBLlo vs. non-MBL controls. Building robust age- and sex-matched reference ranges for the most relevant immune-cell populations in the blood of non-MBL donors is essential to appropriately identify an altered immune status in different clinical settings and highlight the altered immune-cell profiles of MBLlo subjects.