CCL4 and viral infectious disease: NK cells can be rapidly activated to attack certain abnormal cells spontaneously through producing large inflammatory cytokines (eg: TNF-α, IFN-γ etc.)and chemotactic factors (eg: CCL3, CCL4, CXCL10 etc.)in vivo24, especially tumor or virus infected cells, so lack of NK cells increased susceptibility to viral infections and possibility to tumorigenesis35.