Characterization of the Stability of Human and Murine Thymic B Cell/Thymocyte Rosettes and Investigation of Unusual Immunophenotypic Findings

In this study we have used immunohistochemistry to study the controversial expression of CD2 and cytokeratin by thymic B cells and also the expression of the adhesion molecules CD40 and CD80. The B cells were clearly CD2 and cytokeratin negative, however the majority expressed CD40 and some coexpression of CD80 was observed. We have previously observed that human thymic B cells are surrounded by rosetting thymocytes; a relationship which is maintained when cells are cultured. Here we show that the rosettes are remarkably stable in both man and mouse. They are dependent on intact surface protein but not on divalent cations, active metabolism, or components of the cytoskeleton. The rosettes could not be dissociated with antibodies to CD40 or CD80. Failure to consider such a stable rosette structure would result in sampling biases when purifying thymic B cell populations and could also contribute to some of the more unusual phenotypic findings such as the expression of CD2.