CD11b expression divides human B1 cells into two transcriptionally distinct subsets. Gene expression microarray analysis was performed on RNA that was isolated from sort-purified naive (CD20⁺CD27⁻CD43⁻) and memory (CD20⁺CD27⁺CD43⁻) B cells, and from CD11b⁻ and CD11b⁺ B1 cells (CD20⁺CD27⁺CD43⁺), obtained from three normal adult individuals for each B cell population. (A) The expression of coding transcripts with well established annotation (28,688) by CD11b⁺ and CD11b⁻ B1 cells is shown in the form of a Venn diagram. Transcripts differentially expressed twofold or greater by CD11b⁺ B1 cells are shown in light orange, transcripts differentially expressed twofold or greater by CD11b⁻ B1 cells are shown in pink, and transcripts expressed similarly by CD11b⁻ and CD11b⁺ B1 cells are represented by the dark orange overlap. (B) A representative set of genes demonstrating significant expression differences among B cell populations for each individual tested is displayed as a heat map along with gene designations.