Assessment of the Monocyte Subpopulations and M1/M2 Macrophage Ratio in Concentrated Bone Marrow Aspirate

Research Type: Level 2 - Prospective comparative study, Meta-analysis of Level 2 studies or Level 1 studies with inconsistent results Introduction/Purpose: This study aimed to determine the M1/M2 macrophage ratio in concentrated bone marrow aspirate (cBMA) used for osteochondral lesions of the talus (OLTs). Methods: Peripheral blood (PB), bone marrow aspirate (BMA), and cBMA were collected intraoperatively and analyzed using automated cell counting, fluorescence-activated cell sorting, and ELISA for cytokine concentrations. The composition of cBMA was compared between two commercial BMA concentration systems. Results: Thirty-eight patients (mean age 43.2 ± 10.1 years) undergoing surgery for OLTs with cBMA were included. cBMA showed a fold increase of 4.7 for white blood cells, 6.1 for monocytes, 7.9 for lymphocytes, 2.4 for neutrophils, and 9.6 for platelets compared to BMA. The mean M1/M2 ratio was 15.2 ± 12.0 (PB), 20.8 ± 13.3 (BMA), and 22.1 ±16.0 (cBMA). IL-1Ra concentration was highest in cBMA (8243.3 ± 14,837.4 pg/mL) compared to BMA (3143.0 ± 2218.5 pg/mL) and PB (1847.5 ± 1520.4 pg/mL). The IL-1Ra/IL-1β ratio was 790.6 ± 581.9 (PB), 764.7 ± 675.2 (BMA),and 235.7 ± 192.1 (cBMA). No significant difference in the cBMA M1/M2 ratio was found between the Magellan (19.0 ± 11.1) and Angel (24.0 ± 18.3) systems. Conclusion: This prospective study found that the M1/M2 ratio in cBMA was 22.1 ± 16.0, with significant patient to patient variation observed. Overall, there was no statistically significant difference in the M1/M2 ratio across PB, BMA, and cBMA samples. This is the first study to characterize the macrophage subpopulation within cBMA, which may have significant clinical implications in future studies.