The role of humoral factors in the mechanisms of graft-versus-host induced host cell proliferation and lymph node hyperplasia in the rat.

The effect of humoral factors released during systemic graft-versus-host (GVH) reactions on cell proliferation and lymph node enlargement was investigated as follows: 1) Thoracic duct lymphocytes of host origin were cultured in diffusion chambers in the peritoneal cavity of rats undergoing a systemic GVH reaction. On day 7 of the response chamber cell proliferation (as judged by 3H thymidine incorporation) was increased two to four fold over that seen in normal hosts. 2) Serum from (H0 x DA) F1 hybrid rats being repeatedly injected with parental (HO) cells contained a factor that, when preincubated with such parental cells in vitro, was able to augment their ability to produce lymph node enlargement in a local GVH reaction. These results suggest that the host cell proliferation and lymphoid hyperplasia observed during GVH reactions might be the results of long range humoral mechanisms acting alone or in addition to the direct interaction between donor and host cells.