Pivotal Advance: CD45RB glycosylation is specifically regulated during human peripheral B cell differentiation

Abstract

A screen of cell surface markers differentially expressed during peripheral B cell differentiation identified that the CD45RB epitope detected by the mAb MEM-55 was highly expressed on CD27(+) memory B cells and absent on CD27(-) naïve B cells. IgG(+)CD27(-) memory and a previously unacknowledged CD27(-) population in blood also expressed high levels of CD45RB(MEM55). Naïve and memory B cells from tonsils followed the pattern observed in blood, and CD38(high) B cells had a bimodal expression pattern when analyzed using flow cytometry. No CD38(high) GC B cells, however, expressed the CD45RB(MEM55) epitope when assayed using immunohistochemistry. Rather, CD38(high)CD45RB(MEM55high) B cells had a distinct cellular phenotype and were localized outside of GCs. CD45RB epitopes, detected by other antibody clones, were expressed at high levels through B cell differentiation, and no changes in splicing of the CD45RB exon were observed during B cell differentiation. Instead, B cells regulated their expression of the CD45RB(MEM55) epitope through site-specific modifications of an O-linked glycochain. CD4(+) T cells differentially spliced CD45 but did not vary the glycosylation of the CD45RB(MEM55) epitope, and CD8(+) cells modified CD45RB(MEM55) expression in a similar manner as B cells. Monocytes expressed the CD45RB exon but not the CD45RB(MEM55) epitope. As CD45 is a highly expressed tyrosine phosphatase that regulates antigen receptor signaling strength in lymphocytes, we conclude that regulated O-linked glycosylation of CD45RB can be used to follow B cell differentiation and that this regulation may be involved in fine-tuning antigen signaling in the cell.

Translational Mini-Review Series on B cell subsets in disease. Reconstitution after haematopoietic stem cell transplantation – revelation of B cell developmental pathways and lineage phenotypes

“…The splicing pattern of CD45 does not change during peripheral human B cell development, with the longest CD45RABC form being dominant at all stages. However, the expression of the CD45RB MEM55 epitope changes through developmentally regulated glycosylation in human B cells, with high expression on essentially all CD27 + B cells but not on naive or transitional B cells [81]. The CD45RB MEM55 epitope is also present on a minor population of CD27 ‐ B cells that express high levels of IgM (Fig.…”

“…These include CD27 + IgM ‐ IgD + cells and CD27 ‐ class‐switched cells [71,73,80]. Recently, our group found that all memory B cell populations, but not naive cells, express CD45RB MEM55 , possibly making it a better marker for memory B cells than CD27 [81].…”

The Relationship between CD27 Negative and Positive B Cell Populations in Human Peripheral Blood

“…An alternative sorting strategy for separating B cells is to use CD24 and CD38, but the relationship with this strategy and that of using CD27/IgD is not clear cut and multiple subpopulations have differential expression of CD27, IgD, CD24, CD38, and B220 (Sanz et al, 2008). Recently, markers such as CD45RB MEM55 (Koethe et al, 2011) and CD330a (Silva et al, 2011) have been reported as alternative markers to help define human memory B cells. Whether they will prove more useful than current strategies remains to be determined.…”

B-cell subpopulations in humans and their differential susceptibility to depletion with anti-CD20 monoclonal antibodies

“…These memory subpopulations show different frequencies of somatic mutation and different replication histories that are thought to reflect their formation on primary or secondary germinal centres or outside germinal centre reactions [5]. A potential new marker for human memory B-cell subpopulations has been identified recently [6]. A proposal has been made that immunophenotyping of peripheral blood B cells should include the markers CD19, CD20, CD24, CD27, CD38 and IgD to be able to distinguish the major subpopulations [7].…”

“…A proposal has been made that immunophenotyping of peripheral blood B cells should include the markers CD19, CD20, CD24, CD27, CD38 and IgD to be able to distinguish the major subpopulations [7]. More detailed information including separation into further subsets and subtle differences in activation status that may be important when looking at disease states may require use of other markers such as different immunoglobulin isotopes, activation markers or chemokine receptors [6,8-14]. …”