Memory B cells protect from systemic dissemination of MCMV without contribution of NK or T lymphocytes. RAG−/− mice were adoptively transferred with 5 × 106 naive B cells or 5 × 106 B cells from MCMV-infected CD8α−/− mice, treated with depleting anti-CD4 antibodies and infected 5 days after cell transfer with 105 pfu MCMV157luc. (A) Bioluminescence imaging of 5 mice/group at 3, 7, and 10 days after infection. Images were obtained from a 5-minute acquisition, and a pseudocolor scale shows relative photon flux for each image. For comparison, a representative B6 mouse and a B6-RAG−/− mouse infected and imaged in parallel are displayed. (B) Relative organ viral load in 5 to 6 RAG−/− mice transferred with memory B cells (•) or naive B cells (○) 18 days after infection. Luciferase activity was measured in organ homogenates and luciferase relative light units (RLU)/15 μg protein are shown. The relative viral load was lower in the memory B-cell group for all organs (P < .005). (C) Survival curve of 6 RAG−/− mice/group adoptively transferred with B cells from MCMV-infected mice (- - -) or with naive B cells (—). Mice that received memory B cells showed a significantly prolonged survival (P < .001). One animal died of a MCMV-unrelated cause. (D) Neutralizing antibody activity in sera of RAG−/− mice transferred with memory B cells (•) or naive B cells (○). The neutralizing antibody activity was measured in vitro on ST-2 cells using MCMV157luc. The luciferase RLU values after infection with 1.2 × 103 pfu MCMV157luc preincubated with sera are shown. Median values are connected as solid (memory B cells) or dashed (naive B cells) lines.
