5A and data not shown). However, a decrease in CXCR3 surface expression was observed. NK cells did not proliferate, displayed no change in GrzB levels and were unable to lyse K562 cells in response to LASV- and MOPV-infected MΦs (data not shown). NK-cell activation is triggered by some NK-cell surface molecules and receptors. The blockade of CD40L, NKG2D, NKp30, NKp44, or NKp46 with neutralizing Ab had no effect on the expression of NK-cell surface

molecules (data not shown). We show here that cell contacts between NK cells and infected MΦs are essential for activation of NK cells and increase cytotoxicity while they do not seem to be involved in the modulation of CXCR3 expression. We previously showed that Saracatinib in vivo MΦs secrete type I IFNs in response to MOPV infection, but that only low levels of these compounds

are produced during LASV infection. CXCL9, CXCL10, and CXCL11 are secreted in response to type I and II IFNs and bind CXCR3. The presence of type I IFN and CXC chemokines was analyzed in the supernatants of NK/MΦ cocultures. In cocultures Ibrutinib nmr with NK cells, MOPV-, and to a lesser extent LASV-, infected MΦs secreted significant amounts of type I IFN and CXCL11 (Fig. 5B). Neutralizing mAbs directed against IFN-R and IFNα were used to inhibit type I IFN, and NK-cell stimulation by CXCL9, CXCL10, and CXCL11 was prevented with neutralizing mAbs directed against CXCR3 or CXC chemokines themselves. Our experiments with an irrelevant Ab gave results similar to those reported in Fig. 2. The inhibition of type I IFN reduced the increase in CD69 and NKp30 expression (Fig. 5C). However, neutralizing mAbs against type I IFN induced a decrease

in CXCR3 surface expression, although this decrease was smaller than that obtained with the irrelevant Ab. Moreover, we observed a global increase in CXCR3 expression (Fig. 5C). NK-cell proliferation also and the intracellular GrzB expression induced by LASV- and MOPV-infected MΦs were also abolished by the blockade of type I IFN (data not shown). After CXCR3 neutralization, NK cells remained activated in terms of the upregulation of CD69 and NKp30, proliferation and enhanced GrzB expression (data not shown). Neutralizing mAbs against CXC chemokines gave similar results. In addition, they induced a decrease in CXCR3 surface expression, but smaller than that obtained with the irrelevant Ab. Thus, our findings demonstrate that the type I IFN secreted by MΦs are necessary for NK-cell activation during LASV and MOPV infection but CXC chemokines have minor effects. We developed a model of NK cells cocultured with infected APCs, for studies of the role of NK cells and the importance of interactions during LASV and MOPV infections. We used LPS-activated APCs as a positive control for the APC-mediated activation of NK cells. We confirmed that LPS did not activate NK cells directly (data not shown).