Thymocyte rosettes: multicellular complexes of lymphocytes and bone marrow-derived stromal cells in the mouse thymus.

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Abstract
The isolation and purification of multicellular complexes composed of lymphocytes and bone marrow-derived stromal cells (thymocyte rosettes) from the mouse thymus is described. These rosettes are the structural in vitro correlate of in vivo associations between lymphoblasts and I-A/E negative macrophages or medullary I-A/E positive dendritic-like cells. Both types of rosettes are preformed in vivo. The rosette-associated thymocytes display a surface antigen phenotype typical of immature thymocytes. In radiation chimeras, replacement of host thymocytes by injected bone marrow cells follows a regular pattern: donor type T cells appear first at day 11 as clusters around I-A negative macrophages and .apprx. 2 days later as similar clusters associated with either I-A positive cortical epithelial cells or I-A positive medullary dendritic cells. These data suggest a defined sequence of lymphostromal interactions during intrathymic maturation and a rapid proliferation of thymocytes after interaction with stromal cells.