In a review article, based mainly on respiratory allergy models, the authors concluded that the PD-1/PD-L1 interaction seems to induce a Th2 response, with an increase in IL-4, whereas the PD-1/PD-L2 interaction induces a Th1 response with upregulated IFN-γ. This evidence concerns the gene PDCD1LG2 and allergic respiratory disease.