Properties of human thymic B cells.
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.
Spencer
J
J
Dept. of Histopathology, UCMSM, University St, London, U.K.
Choy
M
M
Hussell
T
T
Papadaki
L
L
Kington
J P
JP
Isaacson
P G
PG
D001402:B-Lymphocytes / Q000276:immunology* / Q000648:ultrastructure; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007124:Immunoenzyme Techniques; D007072:Immunoglobulin D / Q000032:analysis; D007074:Immunoglobulin G / Q000032:analysis; D007075:Immunoglobulin M / Q000032:analysis; D007223:Infant; D008213:Lymphocyte Activation / Q000276:immunology; D008934:Mitogens / Q000276:immunology; D013601:T-Lymphocytes / Q000648:ultrastructure; D013950:Thymus Gland / Q000276:immunology* / Q000648:ultrastructure
D007072:Immunoglobulin D; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D008934:Mitogens