CD40LG and infection: The percentage of TCD3+ lymphocytes increased depending on the PiCV infection severity (PiCV viral loads) and was the highest in group S. In contrast, the B IgM+ cells subpopulation was almost two times lower in the birds from group S than in these from group H. The ratio of T CD3+ lymphocytes to B IgM+ varied from 1.6:1 in group H to 11:1 in group S. Those differences suggest that PiCV infection could affect the B lymphocytes.