Introduction: This study investigated the association between natural killer cell activity (NKA) and five complete blood cell count (CBC)-derived inflammatory markers, including neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), systemic immune-inflammation index (SII), and systemic inflammation response index (SIRI). Methods: This cross-sectional study included a total of 10,329 individuals who underwent CBC and NKA tests at Chaum Life Center in Korea between January 2016 and May 2022. NKA was estimated by measuring the amount of interferon-gamma (IFN-γ) released by activated natural killer cells; low NKA was defined as IFN-γ level < 500 pg/mL. Results: The results showed a significant increase in the percentage of subjects with low NKA with increasing CBC-derived inflammatory markers. The odds ratios (ORs) for low NKA were 3.90 (3.45– 4.41), 2.69 (2.38– 3.05), 1.45 (1.29– 1.63), 2.96 (2.62– 3.35), and 4.80 (4.23– 5.45) in the highest quartile of NLR, PLR, MLR, SIRI, and SII, respectively, compared to the lowest quartile. Moreover, NLR, SIRI, and SII showed higher discriminatory performance for low NKA compared with traditional inflammatory markers, such as C-reactive protein (CRP) and white blood cell (WBC) count. Conclusion: These findings indicate that CBC-derived inflammatory markers are associated with low NKA in a large health-screening population, suggesting their potential relevance as indicators of immune–inflammatory status. Keywords: natural killer cell activity, inflammatory marker, complete blood cell count, inflammation, innate immunity
Cho et al. (Sun,) studied this question.