B cell development and proliferation of mature B cells in human fetal intestine

B cells are present in human fetal intestine from approximately 14 weeks of gestation. Here we show that this population includes mature, dividing B cells. These are large cells with dendritic processes, resembling human thymic B cells. In addition, we observed IgM+, light chain−, and CD20− cells and local expression of V pre‐B, demonstrating that the human fetal intestine is a site of B cell development. Ig V H DJ H gene sequencing can confirm clonal identity of B cells. Identification of the same IgV H 4–34 sequence in serial sections in two fetuses confirmed local accumulation of related cells in each case. IgV H 4–34 was also amplified from an additional two samples, and the D and J repertoire compared with a unique database of unselected V H 4–34 genes from postnatal gut. Distinguishing characteristics of Ig λ genes in postnatal gut were also studied in the fetus. According to these parameters, fetal and postnatal B cells are unrelated.