Complement in graft versus host disease: IL Depletion of complement components during a systemic graft versus host...

Serum complement (C) and C components were examined during a systemic graft versus host (GVH) reaction in the rat. In our series of experiments (Lewis times Brown Norway) F-1 hybrid rats (60-80g) were given 200 times 10-6 or 400 times 10-6 Lewis spleen cells intravenously. Clinical GVH disease appeared 5-7 days after cell injection. Five of six rats in the experimental groups had a fall in levels of serum C2 (20-76%) and C4 (75-98%). Only one of six rats in the control group had a significant fall in C components. In a subsequent experiment (Fisher 344 times Brown Norway) F-1hybrid rats (60g) were given 400 times 10-6 Fischer 344 spleen cells or 200 times 10-6 Fischer 344 Ficoll-Hypaque separated spleen lymphocytes. Clincal GVH disease in this instance appeared on day 10. As in the previous experiments C2 and C4 fell markedly, 20-60% and 60-8-%, respectively, from baseline titers. The control groups did not have a significant fall in C2 or C4. Further examination showed reduction in C3, C5, C6,AND C8 suggesting a sequential activation of the C system via the classical pathway. We have postulated that the cells undergoing blast transformation may be activating the C system through membrane changes during the GVH reaction. Furthermore, the deficiency of C AND C components during GVH disease may contribute to the increased susceptibility of the host to infection and sepsis.