Increased beta 2-microglobulin-free HLA class I heavy chain serum levels in the course of immune responses to viral antigens and to mismatched HLA antigens

Besides being present in serum in association with beta 2-mu, HLA class I h eavy chains are also present in serum as beta 2-mu-free moieties. The incre ase in serum levels of beta 2-mu-associated HLA class I heavy chains in con ditions associated with an activation of the immune system have prompted us to measure the serum levels of beta 2-mu free HLA class I heavy chains in the course of immune responses to viral antigens and to mismatched histocom patibility antigens. The serum level of beta 2-mu-free HLA class I heavy ch ains, like that of beta 2-mu-associated HLA class I heavy chains was signif icantly increased in patients affected by advanced HIV-1 infection or by ch ronic hepatitis C (CHC). In the latter group of patients an association was found between a reduction in the beta 2-mu free HLA class I heavy chain se rum level and response to therapy with interferon alpha and ribavirin. More over, the beta 2-mu-free HLA class I heavy chain serum level was increased more than that of beta 2-mu-associated HLA class I heavy chains during epis odes of liver ischemia following liver transplantation and in the course of acute graft rejection and of acute graft-versus-host-disease (GVHD) after allogeneic bone marrow transplantation (BMT). These results suggest that th e serum levels of beta 2-mu-free and beta 2-mu-associated HLA class I heavy chains are independently regulated. Furthermore, beta 2-mu-free HLA class I heavy chain serum level may be a useful marker to monitor response to the rapy in CHC patients and the clinical course of liver and bone marrow graft s.