Increased β2-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 β2-μ, HLA class I heavy chains are also present in serum as β2-μ-free moieties. The increase in serum levels of β2-μ-associated HLA class I heavy chains in conditions associated with an activation of the immune system have prompted us to measure the serum levels of β2-μ-free HLA class I heavy chains in the course of immune responses to viral antigens and to mismatched histocompatibility antigens. The serum level of β2-μ-free HLA class I heavy chains, like that of β2-μ-associated HLA class I heavy chains was significantly increased in patients affected by advanced HIV-1 infection or by chronic hepatitis C (CHC). In the latter group of patients an association was found between a reduction in the β2-μ-free HLA class I heavy chain serum level and response to therapy with interferon a and ribavirin. Moreover, the β2-μ-free HLA class I heavy chain serum level was increased more than that of β2-μ-associated HLA class I heavy chains during episodes 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 the serum levels of β2-μ-free and β2-μ-associated HLA class I heavy chains are independently regulated. Furthermore, β2-μ-free HLA class I heavy chain serum level may be a useful marker to monitor response to therapy in CHC patients and the clinical course of liver and bone marrow grafts. [ABSTRACT FROM AUTHOR]