Neuroimmune semaphorin 4D is necessary for optimal lung allergic inflammation.

•We examined the changes in lung responses to allergen in Sema4D−/− and WT mice.•Allergic lung response was downregulated in Sema4D−/− mice as compared to WT mice.•Sema4D deficiency did not affect lung physiology measured by Buxco machine.•We found a critical costimulatory role for Sema4D in T cell activation.•Sema4D deficiency affects spleen Treg cells but not lung dendritic cells.