ERRATUM
Volume 88, no. 4, p. 2312–2318, 2014. Page 2317, Acknowledgments: Paragraph 2 should be replaced with the following.
This work was supported by Fondo de Investigación Sanitaria (FIS) grant PI11/00127 (funded by the Fondo de Investigación Sanitaria del Instituto de Salud Carlos III, the Ministry of Health of Spain, the State Secretary of R&D, and FEDER/FSE) and Comunidad de Madrid grants UAM-CM-CCG10-4911 and UAM-Banco de Santander to S.G. This work was also partly supported by NIAID grant U19AI083025 to A.G.-S.