CD40LG and infection: Although just a small population of IgM+ B-cells in PBLs were infected by LCDV (from 4% at 1 h to 7% at 6 h), the amount of IgM+ B-cells clearly declined at 1 h (12.1%) as compared to pre-infection (19.9%), reduced to the lowest value at 3 h (10.4%), and then increased but was still lower than pre-infection at 12 h and 36 h (~15%), revealing that LCDV infection facilitated damage to B-cells during the early stage, as proved by TEM results that showed karyopyknosis of the PBLs, cell disruption and apoptosis.