Another very useful diagnostic tool is the detection of interleukin-10 (IL-10) in the serum and aqueous humor produced by malignant B-cells98; IL-10 belongs to the Th2 cytokine group and acts as a “growth factor” for B-cells and therefore contributes to the development and proliferation of PCNSL by inhibiting Th1 cytokines and consequently, T cell cytotoxic effects against malignant B-cells. This evidence concerns the gene IL10 and primary central nervous system lymphoma.