Memory B cells protect from MCMV dissemination in the absence of a functional NK-cell response. (A) MCMV titers and (B) viral DNA copies in lung, spleen, and salivary gland 21 days after infection with 10⁵ pfu MCMV157luc. Results from RAG^−/− mice adoptively transferred with 5 × 10⁶ B cells from MCMV-infected mice (•) or with 5 × 10⁶ naive B cells (○) are shown (median values of 5 mice/group are indicated as lines). In all recipient animals, CD4⁺ and CD8⁺ T cells were depleted 2 days after transfer by application of the appropriate monoclonal antibodies to exclude contribution of T cells to reduction in viral load. There were significantly reduced virus titers in lung and salivary gland in the memory B-cell group (P < .01) and significantly reduced viral DNA copies in all organs (P < .01 for lung and salivary gland, P < .05 for spleen).