T-bet-positive and IRTA1-positive monocytoid B cells differ from marginal zone B cells and epithelial-associated B cells in their antigen profile and topographical distribution.

BACKGROUND AND OBJECTIVES: It remains controversial whether splenic and nodal marginal zone B cells, monocytoid -, and epithelial-associated B cells represent separate B-cell subsets or just variants of the same population. To clarify this issue we studied the antigen profile and topographical distribution of these cell types. DESIGN AND METHODS: We studied samples of toxoplasmic lymphadenopathy, lymph nodes with a developed marginal zone, and hyperplastic palatine tonsils. Deparaffinized sections were subjected to antigen-retrieval pre-treatment then incubated with appropriate antibodies. The bound antibodies were made visible using the alkaline phosphatase anti-alkaline phosphatase method with FastRed as the chromogen.
RESULTS: We found that i) nodal marginal zone B cells have a similar immunophenotype and topographical distribution to their splenic counterparts, ii) monocytoid B cells differ in their antigen profile (presence of T-bet, IRTA1, CD75, CD45RA, absence of BCL-2 , CD21, CD27) from splenic and nodal marginal zone B cells and more closely resemble epithelial-associated B cells (presence of IRTA-1, CD45RA, partial expression of T-bet, CD75, absence of CD21, CD27). Monocytoid B cells were mostly not found in nodal marginal zones when a marginal zone was developed, but were seen in areas adjacent to marginal zones and occasionally in germinal centers. INTERPRETATION AND
CONCLUSIONS: Collectively, our results indicate that monocytoid B cells represent a distinct differentiated B-cell subset, and provide a solid basis for isolation and functional investigations of the cell types studied, and for revising the hitherto inadequate classification of nodal marginal zone lymphomas.