Bidirectional Effects of Interaction between Parental Thymocytes and F1 Spleen Cells in the Production of Graft vs Host Splenomegaly

Abstract

The addition of 1.5 × 10⁷ F₁ spleen cells to inocula of parental thymocytes in sublethally irradiated F₁ hosts influenced the resultant splenomegaly. The influence of the F₁ cells was bidirectional; under certain conditions they increased the splenomegaly while under others they decreased it. Analysis of these conditions revealed that the effect the F₁ cells had depended on the activity of the parental thymocytes. Active thymocytes produced small spleens when inoculated alone; the smaller the spleen the greater the synergy with F₁ cells. On the other hand less active thymocytes occasionally produced some splenomegaly on their own. When they did, added F₁ cells reduced the spleen size (acted “antergistically”). The mechanism(s) by which these bidirectional effects of F₁ cells may be expressed are discussed.