CD4 and Zika virus infectious disease: In this study, we investigated the role of CD4+ T cells in the response to primary ZIKV infection via systemic (intravenous) and sexually transmitted (intravaginal) routes using LysMCre+Ifnar1fl/fl and Ifnar1-/- C57BL/6 mice, as we described previously for investigation of the CD8+ T cell response to ZIKV [22].