Interleukin 33: a switch-hitting cytokine

For many years IL-33 has been widely studied in the context of T helper type 2 (T(H)2)-driven inflammatory disorders. Interestingly, IL-33 has now emerged as a cytokine with a plethora of pleiotropic properties. Depending on the immune cells targeted by IL-33, it is reported to not only promote T(H)2 immunity, but also to induce T helper type 1 (T(H)1) immunity. Furthermore, recent studies have revealed that IL-33 can activate CD8(+) T cells. These new studies provide evidence for its beneficial role in antiviral and antitumor immunity. Here we review the evidence of IL-33 to drive protective T cell immunity plus its potential use as an adjuvant in vaccination and tumor therapy.