Marginal zone B cells in human gut-associated lymphoid tissue

Marginal zone B cells in gut-associated lymphoid tissue (GALT) in humans are those that surround the mantle zone of naïve B cells and that infiltrate into the follicle associated epithelium.  As such they are the B cells located on the boundary between the host and the micobiota and other constituents of the intestinal lumen.  They are considered to be the benign analogues of marginal zone B cell lymphomas of mucosal-associated lymphoid tissue (MALT lymphomas).   The only other lymphoid tissue in the body with a marginal zone, in health, is the spleen.  The splenic marginal zone contains some memory B cells and also B cells responsible for immune responses to TI-2 antigens.  Circulating analogues of marginal zone B cells express CD27 and IgM, and includes subsets that are IgD+ and IgD-.

We have compared marginal zone B cells in human Peyer’s patches to those in spleen and to putative circulating analogues in blood, by immunohistochemistry, flow cytometry and by next generation sequencing of immunoglobulin heavy chain variable region genes. 

We have observed that GALT and splenic marginal zone B cell populations differ markedly in the proportion of B cells that express IgD.  GALT marginal zone B cells are mostly IgD- whilst splenic marginal zone B cells are IgD+.  The alignment of each of these subsets to blood circulating analogues identified by next generation sequencing and to class switch variants with memory B cell phenotypes will be discussed.