L-asparaginase II produced by Salmonella typhimurium inhibits T cell responses and mediates virulence.
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Salmonella enterica serovar Typhimurium avoids clearance by the host immune system by suppressing Tcell responses; however, the mechanisms that mediate this immunosuppression remain unknown. We show that S. Typhimurium inhibit Tcell responses by producing L-Asparaginase II, which catalyzes the hydrolysis of L-asparagine to aspartic acid and ammonia. L-Asparaginase II is necessary and sufficient to suppress Tcell blastogenesis, cytokine production, and proliferation and to downmodulate expression of the Tcell receptor. Furthermore, S.Typhimurium-induced inhibition ofTcells invitro is prevented upon addition of L-asparagine. S.Typhimurium lacking the L-Asparaginase II gene (STM3106) are unable to inhibit Tcell responses and exhibit attenuated virulence invivo. L-Asparaginases are used to treat acute lymphoblastic leukemia through mechanisms that likely involve amino acid starvation of leukemic cells, andthese findings indicate that pathogens similarlyuse L-asparagine deprivation to limit Tcell responses.