Differentiation-associated cellular complex formation of murine thymocytes with thymic stromal cells

Properties of normal murine thymocytes forming in vitro cellular complexes with thymic epithelial-like stromal cells in the form of pseudoemperipolesis were studied. The complex-forming cells were low-buoyant-density blasts primarily localized to the subcapsular zone. After transition into small cortical lymphocytes, their capacity for complex formation was lost. The complex-forming cells were relatively resistant to cortisone acetate and low-dose (170 rads) whole-body X-irradiation. Their number increased sharply in the early stage of thymic regeneration, corresponding to an increase in the percentage of large thymic lymphocytes 4 to 5 days after cortisone treatment or X-irradiation. However, after the thymus was repopulated with small lymphocytes, the percentage of complex-forming lymphocytes decreased rapidly to the normal level. A possible relationship between a step in thymic leukemogenesis and intrathymic T-cell differentiation is discussed.