JOINT INFLUENCE OF NATURAL KILLERS (NK) AND HEMATOPOIETIC STROMA ON REJECTION OF PARENT STEM-CELLS

The growth of hemopoietic stem cells of C57BL/6 mice was explored in s yngeneic and semi-syngeneic foci of heterotopic hemopoiesis, formed un der the kidney capsule of (CBA x C57BL/6)F-1 recipients with and witho ut prior treatment with cyclophosphamide or fractionated irradiation, which is known to abrogate hybrid resistance and NK cell activity. Our results show that the suppression of the growth of parent stem cells in semi-syngeneic F-1-recipients is due to NK cell participation, Howe ver, no inhibition was found in the growth of identical cells in the f oci of syngeneic hemopoietic stroma in the same recipients, despite th e presence of NK cell activity. The experimental model used shows clea rly that hybrid resistance is the result of the joint involvement of N K cells and the semi-syngeneic stroma.