ARG1 and neoplasm: Furthermore, some parasites, like Leishmania donovani, compete with macrophages and other host cells for metabolic nutrients and energy for survival and replication.[179] Arginase activity in macrophages may be induced by the microbiota in amino acid metabolism, thus increasing Arg‐1 production; excessive Arg‐1 can accelerate the synthesis of ornithine and then prompt collagen synthesis and tumor cell growth.