TOX, HOPX, COCH, and SOX7 display a markedly different expression between MZB and switched B cells. (A) Splenic IgG⁺CD27⁺ and IgD⁺CD27⁺ (MZB) cells were sorted from either 10 or 11 spleen samples from donors of different ages (see Materials and methods) and their gene expression profiles were determined. The 50 genes that achieve the highest difference in expression (P < 0.05) between those two subsets in spleen are shown (left, up-regulated genes in IgG⁺CD27⁺; right, up-regulated in MZB cell; the log₂ scale bar is indicated), with spleen samples arrayed by increasing age. The same comparison was made for blood IgG⁺CD27⁺ and MZB IgD⁺CD27⁺ (not depicted) to establish a list of the 50 most discriminating genes. The discriminating genes that are shared between the blood and spleen comparisons are identified by asterisks, and the four genes studied by qPCR are boxed. (B) MZB, naive, and switched IgG⁺CD27⁺ cells from splenic samples of four different children were obtained by two consecutive sorts (see Materials and methods). Relative expression levels of SOX7, TOX, COCH, and HOPX in each subset were determined by qPCR. Expression values normalized by B2M expression were calculated by the comparative method, normalizing to 1 the expression of the different genes in the MZB fraction. Mean values ± SEM of three independent experiments done in triplicates are shown. **, P < 0.01; paired, two-tailed Student’s t test.