Thus, endogenous histamine in H4R- deficient mice produced a reduction of the tumour size and decreased percentages of CD4+ T cells and Tregs (CD4+CD25+FoxP3+) in TDLN compared with wild-type mice.23 To further reinforce the important role of H4R in immunosurveillance, the present findings show negative correlations between the tumour-infiltrating cytotoxic subsets, CD8+ T lymphocytes and NK cells, and the tumour weight, which were only observed in histamine-treated H4R-KO mice. Here, HRH4 is linked to neoplasm.