Labeled leukocyte inflammation imaging: Comparison of microfluidic chip isolated leukocytes with conventionally isolated leukocytes

Objectives To compare labeled leukocyte (WBC) inflammation imaging using WBCs isolated by microfluidic chip with WBCs isolated by conventional methodology (hydroxyethyl starch augmented gravity sedimentation/centrifugation).

Methods Inflammation was induced in 23 F-344 rats by injecting 0.1 mL pure turpentine oil in the right thigh. 48 hrs later 60 mL blood was withdrawn from 1 human donor & divided into two 30 mL aliquots (A & B). A WBCs were isolated by conventional method. B WBCs were isolated by microfluidic chip, using size based sorting. After isolation A & B WBCs were labeled with 27.8 MBq ¹¹¹In-oxine (In) using routine methods. A & B InWBC labeling efficiency, viability (trypan blue exclusion) & concentration per mL were determined. Animals were divided in 3 groups & injected via tail vein. Group 1 (n=8) was injected with 3.7 MBq A InWBC; Group 2 (n=8) with 3.7 MBq B InWBC; Group 3 (n=7) with 2.4 MBq B InWBC. 24 hrs. later 5 min images of the animals were obtained with a gamma camera with parallel hole collimator (pixel size = 2.3 mm). Animals then were sacrificed & activity in inflamed & normal tissue determined. Inflamed/normal tissue ratios were generated.

Results A InWBC labeling efficiency was 88%, B was 94%. A & B InWBC viability were 98%. B InWBC concentration was nearly 30% more (27x10⁶/mL) than A (19x10⁶/mL). Visually, InWBC activity was more intense in Groups 2 & 3 than in Group 1. Mean inflamed/normal tissue activity ratio was significantly higher in Groups 2 (9.3±0.7, p=0.02) & 3 (9.2±1.2, p=0.04) than in Group 1 (6.5±2.8).

Conclusions In this investigation, microfluidic chip isolated leukocytes enhanced InWBC accumulation in inflammation. Implications of this observation include potentially improved test sensitivity, reducing amount of radioactivity injected & availability of WBC imaging for patients with reduced levels of circulating leukocytes.

Research Support This work was supported in part by National Institute Of Biomedical Imaging and Bioengineering Award P41EB002503 to BioMeMs Resource Center at Massachusetts General Hospital