Age‐Matched Reference Values for Circulating Natural Killer T ( <scp>NKT</scp> )‐Like Cells

Natural Killer T-like cells are T lymphocytes characterised by the expression of CD56 accompanied by perforin and granzyme B production, typical of cytotoxic cells and the innate immunity compartment. Imbalance in their distribution could occur in pathological conditions, including solid or haematological cancers, autoimmune disorders and metabolic diseases; therefore we aimed to define age-matched reference values of the NKT-like population. NKT-like cell count and their expression of CD4 and CD8 surface antigens were evaluated in 2208 subjects by flow cytometry, with a lyse-no-wash protocol in a CE-IVD workup. Outpatients without alteration of any laboratory test and adult healthy volunteers were used to determine NKT-like age-matched reference values; a total of 490 subjects divided into six age ranges were finally enrolled. We defined reference values for NKT-like cells in adult and in 5 age-matched paediatric control groups. NKT-like cell number increases with age both in percentage and absolute count. While NKT-like/CD8+ cells increased with age, NKT-like/CD4+ cells showed an opposite trend. Similarly, double-positive cells (NKT-like/CD4+ CD8+) gradually decreased with age, while double-negative cells (NKT-like/CD4-CD8-) increased up to 16 years and then decreased in adults. Ultimately, we evaluate adult and paediatric patients with NKT-like cell count outside normal ranges derived here to highlight the principal associated conditions that may be involved. Our paper is a first step toward the definition of robust reference values for NKT-like cell subpopulations under the CE-IVD conditions. Providing NKT-like cell number and frequency in the diagnostic report appears helpful to better delineate the immune profile of patients.