BACKGROUND: Treatment with the TRPV1 agonist, capsaicin, was previously shown to protect against experimental colitis in the severe combined immunodeficiency (SCID) T-cell transfer model. Here, we investigate trpv1 gene expression in lymphoid organs and cells from SCID and BALB/c mice to identify a potential target for the anti-inflammatory effect of capsaicin.

METHODS: The trpv1 expression was studied by real-time PCR in lymphoid tissues and gut of untreated and capsaicin-treated colitic SCID mice. Effects of capsaicin and a TRPV1 antagonist on T cells were studied in vitro.

RESULTS: In contrast to BALB/c mice, spleen, lymph nodes, and rectum of colitic and noncolitic SCID mice express trpv1 mRNA. Capsaicin treatment in vivo attenuated T-cell transfer colitis and capsaicin in vitro also attenuated T-cell proliferation induced by enteroantigen, mitogen, and anti-CD3/CD28 beads in BALB/c, C57BL/6 mice, and B6.129X1-trpv1tm1Jul/J trpv1 knockout mice. Proliferation and cytokine secretion were fully comparable in mice with and without trpv1 expression. Likewise, enteroantigen- and mitogen-stimulated T cells from wild-type and trpv1 knockout mice were equally inhibited by capsaicin. Surprisingly, the TRPV1 antagonist BCTC also inhibited enteroantigen- and mitogen-induced T-cell proliferation.

CONCLUSIONS: The trpv1 mRNA expression in lymphoid organs and the rectum of SCID mice suggests that the TRPV1 signaling in these organs could play a role in capsaicin-mediated attenuation of colitis. In addition, capsaicin-induced inhibition of T-cell proliferation of wild-type T cells lacking trpv1 expression suggests that capsaicin inhibits colitogenic T cells in a TRPV1 receptor-independent way, which might be linked to its anti-inflammatory effect.