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

Objective The purpose of this study was to determine the M1/M2 macrophage ratio in concentrated bone marrow aspirate (cBMA) in patients undergoing surgical intervention augmented with cBMA for osteochondral lesions of the talus (OLTs).Design Samples of peripheral blood (PB), bone marrow aspirate (BMA), and cBMA were collected during the procedure. The samples were analyzed by automated cell counting and multicolor fluorescence-activated cell sorting with specific antibodies recognizing monocytes (CD14+ CD16+) and the M1 (CD86+) and M2 (CD163+CD206+) populations within that monocyte population. Cytokine concentrations within the samples were evaluated with enzyme-linked immunosorbent assay (ELISA). The composition of cBMA was compared between 2 commercially available BMA concentration systems.Results Thirty-eight patients with a mean age of 43.2 +/- 10.1 years old undergoing a surgical procedure for the treatment of OLTs involving the use of cBMA were included. cBMA had a mean fold increase of 4.7 for all white blood cells, 6.1 for monocytes, 7.9 for lymphocytes, 2.4 for neutrophils, and 9.6 for platelets when compared to BMA. The mean M1/M2 ratio for PB, BMA, and cBMA was 15.2 +/- 12.0, 20.8 +/- 13.3, and 22.1 +/- 16.0, respectively. There was a statistically significant higher concentration of interleukin-1 receptor antagonist (IL-1Ra) in the cBMA sample (8243.3 +/- 14,837.4 pg/mL) compared to both BMA (3143.0 +/- 2218.5 pg/mL) and PB (1847.5 +/- 1520.4 pg/mL) samples. The IL-1Ra/IL-1 beta ratio for PB, BMA, and cBMA was 790.6 +/- 581.9, 764.7 +/- 675.2, and 235.7 +/- 192.1, respectively. There was no difference in the cBMA M1/M2 ratio (19.0 +/- 11.1 vs 24.0 +/- 18.3) between the Magellan (Isto Biologics, Hopkinton, Massachusetts) and Angel systems (Arthrex Inc, Naples, Florida).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.