CD4 and infection: Peripheral blood samples, collected on the third day post-infection prior to sacrifice, were processed with Gey’s solution to remove red blood cells and resuspended in PBS supplemented with 2% BSA; then, the cells were stained with a combination of B220-APC, Mac-1-PECy7, and Gr-1-PE for B cells and myeloid cells or stained with a combination of CD3-Alexa Fluor 700, CD4-APC, CD8-BUV805, and CD25-FITC for T cells.