Quantification of Islet Cell Cluster Size Heterogeneity in Early Postnatal Porcine Pancreas

Donor scarcity limits islet transplantation for type 1 diabetes. Early postnatal piglets are a potential xenogeneic source of endocrine tissue, yet their immature islet cell clusters (ICCs) remain insufficiently characterised with respect to size and maturation. Here, we quantified ICC size heterogeneity in pancreata from six 14-day-old piglets using insulin and glucagon immunofluorescence staining and large-area immunofluorescence imaging with automated whole-section analysis. ICCs were classified as small (1-2 endocrine cells), intermediate (3-5 endocrine cells), or large (≥6 endocrine cells). Well-developed ICCs reaching ∼100 µm in diameter were consistently identified in all animals and exhibited an intermingled β- and α-cell cytoarchitecture similar to that of adult pig and human islets. The densities of small, intermediate, and large clusters were largely comparable among littermates and across piglets, suggesting a consistent distribution of ICC size classes at this postnatal age. Quantitative composition analysis revealed a strong predominance of insulin-positive area. In small and intermediate ICCs, we observed mean β/α cell ratios of 3.7 ± 0.4 and 3.8 ± 0.4, respectively. In large ICCs, the proportion of glucagon staining was significantly higher, decreasing the β/α cell ratio to 2.2 ± 0.3. Together, these data point to a reproducible distribution of ICC sizes in 14-day-old piglet pancreata, including a population of morphologically well-developed, ∼100 µm-sized clusters. These findings from native pancreatic tissue provide a morphological basis for further evaluating 14-day-old piglets as a potential donor source for xenogeneic islet transplantation.