Given the task definition and input, reply with output. Given a passage with a context and an answer, construct a question on the basis of the information present in the passage. Construct the question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) it answer uses text phrases from the passage. Avoid creating questions that (i) can't be answered correctly without actually understanding the passage and (ii) uses the same words or phrases given in the passage.

Context: Complement protein C4d has been used as a marker of antibody mediated rejection in kidney allografts. C4d has been shown to be deposited also in chronic kidney allograft rejection, and frequently in acute liver allograft rejection. In chronic liver allograft rejection there is limited data of C4d positivity.', '7 liver allografts explanted at retransplantation due to chronic rejection were examined for expression of C4d. Immunoperoxidase technique on frozen sections was used. The "zero" biopsies of the same livers at the first transplantation served as controls.', 'Expression of C4d was significantly increased in portal and central veins as well as in the portal stroma of the grafts with chronic rejection when compared to the expression at implantation of the graft.
Answer: The complement system and anti-donor antibodies may contribute to the process of chronic allograft rejection in the liver.
Is vascular deposition of complement C4d increased in liver allografts with chronic rejection?