When γδ T cells were silenced via injection of anti-γδTCR mAb 3 days (Supplementary Fig. 7b, c) or thymectomy was performed 24 h, before viral infection, differentiation of B-1a cells was severely impaired in mice as revealed by marked decline in frequencies of CD19+CD43+CD5+IgM+HA+ (Supplementary Fig. 7d) and CD38+CD138+HA+ (Supplementary Fig. 7e) B-1a cell populations in the infected lungs. Here, CD40LG is linked to viral infectious disease.