The expression of human insulin protein was analysed using western blotting and immunocytochemistry assays. (A) The result of western blotting shows that mature human insulin was secreted by engineered L-cells. Total protein was extracted from L-1 and L-2. (B) Immunocytochemistry assay confirmed insulin expression in the L-cells. The green sections show that the cytoplasm of the cells expresses human insulin, and the blue sections are nuclei stained by DAPI.