In T2DM patients, the distribution of the percentages of CD8-positive cells, CD3-positive cells, CD56-positive cells, and the CD4/CD8 ratio differed significantly across the various serum 25(OH)D3 concentration ranges (Table 4), with the clear progressive trends in CD8 and CD4/CD8 suggesting the induction of a Th1 immune marker profile in 25(OH)D-deficient patients. Here, CD8A is linked to type 2 diabetes mellitus.