Enhanced IFN-gamma secretion by human NK cells upon simultaneous engagement of NKG2D and direct stimulation with agonists of TLR3 or TLR7 and IL-12.

MARÍA VICTORIA GIRART; MERCEDES BEATRIZ FUERTES; CAROLINA INES DOMAICA; LUCAS EZEQUIEL ROSSI; NORBERTO WALTER ZWIRNER

Rio de Janeiro, Brasil

Congreso; 13º Congreso Internacional de Inmunología; 2007

Sociedad Brasilera de Inmunología

NK cells express different TLRs such as TLR3, TLR7 and TLR9, but little is known about their role in NK cell stimulation. In this work, we used specific agonists (polyI:C, loxoribine and ODNs) to stimulate human NK cells without or with suboptimal doses of IL-12, IL-15 or IFN-a, and investigated the secretion of IFN-g, cytotoxicity and expression of the activating receptor NKG2D. PolyI:C and loxoribine, in conjunction with IL-12 but not IL-15, promoted a robust secretion of IFN-g, which required internalization of the TLR agonists and was dependent on MEK1/ERK, p38 MAPK, p70S6 kinase and NF-kB but not on calcineurin. IFN-a induced a similar effect but promoted lesser IFN-g secretion. However, cytotoxicity (51Cr release assays) against MICA- and MICA+ tumor targets remained unchanged as well as the expression of the NKG2D receptor. Excitingly, IFN-g secretion was significantly increased when NK cells were stimulated with polyI:C or loxoribine and IL-12, and NKG2D engagement was induced by coculture with MICA+ tumor cells but not with MICA- tumor cells, an effect that was dependent on PI3K. We conclude that resting NK cells secrete high levels of IFN-g in response to agonists of TLR3 or TLR7 and IL-12, and this effect can be further enhanced by co-stimulation through NKG2D. Therefore, an integration of the signaling cascades that involve TLR3, TLR7, IL-12 and NKG2D is critical to promote robust IFN-g-dependent NK cell-mediated effector functions which could be a strategy to promote Th1-biased immune responses in pathological situations such as cancer.