The requirement of viable thymocytes for species-specific attachment to and release from macrophages.

The role of the thymocyte in its species-specific binding to macrophages has been explored. Although formalin treatment of macrophages resulted in loss of binding to thymocytes, formalin treatment of thymocytes did not have this effect. However, two differences between living and formalin-treated thymocytes were noted. Formalin-treated thymocytes bound to macrophages of any species whereas the binding of living thymocytes was species specific. Living thymocytes attained maximum binding in approximately 1 hr and then the fraction bound gradually diminished. Formalin-treated thymocytes remained bound to the macrophage and appeared to be phagocytized. Released thymocytes did not bind to fresh macrophages, but released macrophages bound to fresh thymocytes. The results suggest that the binding of thymocytes to macrophages results in maturation of thymocytes.