TH17 cells thrive and react to the OVA antigen in mice lacking CD11b.

The immune system takes its cues from antigen-presenting cells (APCs) to either go on the offensive against a foreign enemy or to stand down and tolerate a harmless threat. Ehirchiou et al. (page 1519) now report a new mechanism by which APCs power down the immune system: an APC surface receptor suppresses the development of overzealous T helper (Th)-17 cells.

According to dogma, APCs that have only few costimulatory receptors dampen immunity. These APCs can't give T cells the stimulatory boost they need to become offensive. But some APCs with lots of costimulatory receptors can somehow still keep T cells in low gear.

One APC receptor that might direct this alternative pathway, the authors hypothesized, is CD11b. Mice need this integrin to remove neutrophils and macrophages from infection sites and subdue...

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