BACKGROUND: Urate through Nacht Domain, Leucine-Rich Repeat, and pyrin domain-containing protein 3 (NALP3) dependent caspase-1 activation stimulates macrophages to secrete inteleukin-1β (IL-1β). Purinergic receptor P2X7 plays a role in the urate induced NALP3 activation. Urate also enhances adaptive immunity indirectly through its effect on antigen presenting cells. In this study, the direct effect of urate on primary human lymphocytes was evaluated.METHODS: Lymphocytes were cultured with or without monosodium urate crystals in the presence or not of a P2X7 inhibitor. Caspase-1 activity was assessed colorimetrically in cell lysates and IL-1β was measured in supernatants with ELISA. Whole lymphocyte viability and proliferation, as well as T-cell proliferation were assessed by means of 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay and of flow cytometry respectively.RESULTS: Urate induced caspase-1 activation and IL-1β release by lymphocytes. It also induced proliferation of whole lymphocytes and T-cells as well. P2X7 inhibitor abrogated lymphocyte proliferation.CONCLUSIONS: Urate, a well defined danger signal, stimulates directly human lymphocytes in a P2X7 dependent way. The subsequent IL-1β secretion could enhance inflammation, whereas expansion of lymphocyte clones could facilitate a subsequent adaptive immune response.