In vitro generation of soluble suppressor factor in murine chronic graft versus host (GVH) disease.

Veto cells are cells which suppress self directed cytotoxicity (CTX) regardless of the strain of origin of the cytotoxic effector cell. The mechanism by which veto cells inhibit self directed CTX is largely unknown. We have previously described the emergence of a veto cell in murine chronic graft versus host (CGVH) disease both in vivo and in vitro. Using an in vitro system in which veto cells are induced, we now report that a soluble factor is also induced which is capable of suppressing CTX. This cytotoxicity suppressing factor (CsF) is heat labile and has a molecular weight above 50 kD. The factor prevents the emergence of a cytotoxic effector cell. but is largely ineffective once the effector cell has functionally emerged. CsF is irreversible and is not restricted in its ability to inhibit anti-self CTX.