Our previous data revealed that proinflammatory IL‐17A‐producing Th cells were enriched predominantly in the blood of GC patients,15 here, our present study have further demonstrated that, in GC tumor tissues, activated neutrophils induce IL‐17A‐producing Th subset polarization through TNF‐α‐B7‐H2‐dependent pathway, and that subsequently IL‐17A‐producing Th subsets exert protumorigenic effects through inflammatory molecule IL‐17A. Here, ICOSLG is linked to gastric cancer.