The Identification of an Ia⁺ Ig^- Thy-1^- Cell in Bone Marrow

Mouse bone marrow contains 10–20% of cells which type as being Ia⁺. A proportion of these are Ia⁺ Ig⁺ B cells and a very small number are IJ⁺ Thy⁺ T cells. When both T and B cells are removed, by separation on isopaque ficoll, a constant 5–10% of cells remain which are Ia⁺ Ig^- Thy-1^-. These cells do not adhere to carbonyl iron, but show some affinity for nylon wool. Using a variety of strains and antisera, it is clear that this cell does not carry determinants of the IJ, IE or IC subregions but can be readily detected with antisera to the IA subregion. The cells are present in mice lacking T cells: nude, ATXBM, ALS-treated and are therefore, presumably, not related to the later stage of T cell differentiation.