Utilisation of whole slide image analysis to quantify lesion formation, collagen content and cell density within histologically stained fibrotic lung tissue

Detailed assessment of therapeutic response in the bleomycin (Bleo)-induced rat model is challenging due to the inability to accurately quantify specific morphological and cellular components within the tissue. This study aimed to utilise histology plus whole slide image analysis to quantify lesion formation and content within lung tissue from Bleo treated rats. Male SD rats, n=5 per group (Gr), were treated with either saline (Gr1) or 1.0mg/Kg Bleo (Gr2) each day for 7 days. On day 22, lungs were fixed, paraffin embedded, sectioned and histologically stained with Picrosirius Red. Whole slide images of lung tissue were captured and analysis algorithms developed by OracleBio (using Indica Labs HALO® software) to define specific regions of interest (ROI) per section including Parenchyma and Lesion, excluding basal collagen. Collagen content and cell density was then quantified within the Lesion and Parenchyma ROI. Mean % Lesion area in Gr2 was 13.4% (95% CI: 8.2 to 18.5). Mean % collagen in Gr2 Parenchyma ROI (6.3%; 5.3 to 7.3) was significantly lower compared to Gr2 Lesion ROI (24.6%; 22.4 to 26.7), but significantly higher compared to Gr1 Parenchyma ROI (3.6%; 2.9 to 4.4). Mean cell density per mm2 in Gr2 Parenchyma ROI (3,254; 3,083 to 3,426) was significantly lower compared to Gr2 Lesion ROI (9,330; 8,633 to 10,027) but not significantly different to G1 Parenchyma ROI (2,899; 2,291 to 3,506). Whole slide image analysis can be used to accurately assess and better interpret therapeutic effects on morphological and cellular tissue parameters within histologically stained lung tissue sections from pre-clinical fibrosis models.