Marginal Zone (MZ) B cells play an important role in the clearance of blood borne bacterial infections via rapid T‐independent IgM responses. We have previously demonstrated that MZ B cells respond rapidly and robustly to bacterial particulates. To determine the MZ‐specific genes that are regulated to allow for this rapid response, resting MZ and Follicular (FO) B cells were sort‐purified and analyzed via DNA microarray. We identified 181 genes that were significantly different between the two cell populations. 92 genes were more highly expressed in MZ B cells while 81 genes were more highly expressed in FO B cells. To further understand the molecular mechanisms by which MZ B cells respond so rapidly to bacterial challenge, idiotype positive and negative MZ B cells were sort‐purified before (0 hour) or after (1 hour) i.v. immunization with R36A, heat killed Streptococcus pneumoniae, and analyzed via DNA microarray. We identified 189 genes specifically up‐regulated (> 5‐fold) and 192 genes specifically down‐regulated (> 10‐fold) by 1 hour after immunization in the idiotype positive MZ B cells. These data provide unique insight into the gene expression pattern in resting MZ vs. FO B cells and idiotype positive MZ B cells following activation, providing new candidate genes and pathways to explore.

Marginal Zone (MZ) B cells play an important role in the clearance of blood borne bacterial infections via rapid T‐independent IgM responses. We have previously demonstrated that MZ B cells respond rapidly and robustly to bacterial particulates. To determine the MZ‐specific genes that are regulated to allow for this rapid response, resting MZ and Follicular (FO) B cells were sort‐purified and analyzed via DNA microarray. We identified 181 genes that were significantly different between the two cell populations. 92 genes were more highly expressed in MZ B cells while 81 genes were more highly expressed in FO B cells. To further understand the molecular mechanisms by which MZ B cells respond so rapidly to bacterial challenge, idiotype positive and negative MZ B cells were sort‐purified before (0 hour) or after (1 hour) i.v. immunization with R36A, heat killed Streptococcus pneumoniae, and analyzed via DNA microarray. We identified 189 genes specifically up‐regulated (> 5‐fold) and 192 genes specifically down‐regulated (> 10‐fold) by 1 hour after immunization in the idiotype positive MZ B cells. These data provide unique insight into the gene expression pattern in resting MZ vs. FO B cells and idiotype positive MZ B cells following activation, providing new candidate genes and pathways to explore.