Decreasing lymphocyte proliferation is a crucial effect of MMF administration and is concentration‐dependent.5, 28 Regulating an inappropriate immune response by inhibition of T cells is important because T cells contribute to autoimmune diseases by multiple stimulatory, activation, and cytotoxic mechanisms.29, 30 In our study, total PBMC numbers of the cats remained largely unaffected by the PO MMF, as did CD4+/CD8+ T‐cell ratios. Here, CD8A is linked to autoimmune disease.