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  • Title: Properties of human thymic B cells.
    Author: Spencer J, Choy M, Hussell T, Papadaki L, Kington JP, Isaacson PG.
    Journal: Immunology; 1992 Apr; 75(4):596-600. PubMed ID: 1592434.
    Abstract:
    B cells, distinct from those seen in myasthenia gravis, are present in normal human thymic medulla, concentrated around the Hassall's corpuscles. We have shown that they constitute 33 +/- 4.8% of the total cells in the thymic medulla. In tissue sections they were often seen to have rosettes of thymocytes around them, a relationship which was maintained when the cells were isolated from the thymus. Thymic B cells expressed cytoplasmic immunoglobulins IgD, IgM and IgG but only rarely IgA. Unlike murine thymic B cells, human thymic B cells were CD5-. Freshly isolated thymic B cells were activated cells, but they rapidly became quiescent and died in culture over a 10-day period unless stimulated with mitogens. Thymic B cells responded to polyclonal B-cell activators SAC and TPA and when stimulated, maintained their relationship with thymocytes. Electron microscopic studies showed that two morphologically different thymocyte populations associated with the B cells. The plasma membranes of larger thymocytes were juxtaposed to the B-cell membrane, but smaller thymocytes with darker cytoplasm were associated with the B cells via cytoplasmic strands. Studies in mice have suggested that B cells are involved in thymic negative selection. The close association between activated B cells and thymocytes observed in this study supports this hypothesis.
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