Abstract: The expression of surface IgD on murine splenic B cells and the regulation of sIgD expression by different stimuli were studied in this paper.The results demonstrated that splenic B cells form two major populations.The high-density small splenic B cells have the phenotype of sIgDhigh and sIgDlow B cells fall into low-density large population.Activation of resting B cells with LPS and anti-IgM induces differences in the level of IgD.Stimulation of resting B cells with LPS decreases the level of sIgD,but sIgD remains high after anti-IgM stimulation.Additional stimulation of Ril-6 following anti-IgM stimulation can lead to decrease the level of sIgD.Taking those together,we conclude that the expression of sIgD goes down following B cell activation.