Characterization of Late Transitional B Cell Subsets in the Murine Spleen

My research is focused on the characterization of B cell subsets present in the murine spleen and their place in the B cell maturation scheme. I am particularly interested in the transitional B cell populations and also a pre-MZ population that was initially considered to be one of the transitional subset.

In the bone marrow of adult mice, B cell development leads to the production of IgMhi immature B cells. Upon reaching the immature stage, B cells home to the spleen where final maturation takes place. In the spleen, immature B cells are termed transitional and two stages have been identified. T1 cells are recent IgMhi bone marrow émigrés, and T2 cells represent more mature cells attempting incorporation into the long-lived peripheral pool. Of interest, two phenotypically different T2 populations have been described in the literature. One T2 population is contained within the IgMhi, CD21hi, CD23hi subset (CD21hi T2) while other T2 cells are found within the IgMhi, CD21lo, CD23hi population (CD21lo T2).

My research project is to characterize the different transitional populations that have been defined and determine which of these populations is the actual late transitional population. My research also focuses on determining the developmental stage of various splenic B cell populations. We utilized multi-parameter flow cytometric analysis to detail the phenotype of T1 cells and both T2 populations, and compared them with mature B cell subsets: marginal zone (MZ) and follicular B cells. Our results demonstrate the CD21lo T2 cells to exhibit an immature phenotype and CD21hi T2 B cells to resemble the more mature MZ B cells. The numbers of CD21hi T2 cells also correlated with MZ size. These results suggest CD21lo T2 cells to be direct progeny of T1 cells, whereas CD21hi T2 cells are likely to be more mature and potentially share a lineage relationship with MZ B cells.

Verma S, Alexander CM, Carlson MJ, Tygrett LT, Waldschmidt TJ. B-cell studies in chronic ethanol mice. Methods Mol Biol. 2008;447:295-323. PubMed PMID:18369926.

Verma S, Waldschmidt TJ. Characterization of splenic CD21hi T2 B cells.Immunol Res. 2007;39(1-3):240-8. Review. PubMed PMID: 17917068.