Analysis of synthetic sites of fourth and fifth components of serum complement system in allogeneic bone marrow chimaeras.

Synthetic tissue sites for the fourth and fifth components of complement (C4 and C5) have been investigated using allogeneic bone marrow chimaeras in mice. One group of chimaeric mice was prepared by transplanting bone marrow cells from C5-sufficient donor mice into irradiated C5-deficient recipients or vice versa, and another group was prepared by transplanting marrow cells from mice that produce high levels of C4 into irradiated recipients that are characterized by having low levels of C4 or vice versa. In such chimaeras, lymphoid cells and serum immunoglobulin allotypes were shown to be exclusively of donor origin. However, haemolytic activities of sera from the chimaeras were consistently identical with those of normal mice of the recipient strain. Similar results were obtained when the complement component levels of the sera were evaluated by double diffusion assays. C4 or C5 antigens were detected in sera of the chimaeras only when recipients were strains that are characterized by having high C4 level or were C5-sufficient mice, respectively. These findings indicate that circulating C4 or C5 complement components present in the blood are not synthesized primarily by cells that are descendants of bone marrow cells in these chimaeric mice.