RTECs make arginase 1, thereby lowering the amount of arginine in the environment and limiting the use of this nutrient by infiltrating T cells.117 In the lupus kidney environment, high IL-23 levels suppress arginase 1 production by RTECs, resulting in more arginine availability and increased local T-cell proliferation and activation.117 In sum, however, caution is warranted as many of the described pathways have not been investigated in a lupus model, and thus the balance of pro- and anti-inflammatory functions of RTECs in lupus remains unknown. The gene discussed is ARG1; the disease is systemic lupus erythematosus.