Soluble HLA antigens, anti-HLA antibodies, and antiidiotypic antibodies in the circulation of renal transplant recipients.

Chronic rejection represents the major threat to long-term survival of organ allografts. It is presumed that this form of rejection is mediated by antibodies against mismatched HLA antigens of the graft. The presence and specificity of anti-HLA-antibodies in posttransplantation sera are, however, difficult to document. We have explored the possibility that anti-HLA antibodies form immune complexes with soluble HLA antigens released from the injured graft and/or that they are blocked by antiidiotypic, anti-anti-HLA-antibodies. Our data demonstrate that the long-term survival of renal allografts is significantly lower in patients who develop anti-HLA-antibodies following transplantation than in patients who do not form antibodies. Following depletion of soluble HLA antigens by magnetic immunoaffinity, we could identify anti-HLA-antibodies in 57% of the sera obtained from patients undergoing chronic rejection of kidney allografts, compared with 41% prior to antigen depletion. In patients tolerating the graft for 4 years or more, the corresponding frequencies of antibody-positive sera was 2% and 5% prior and following depletion of HLA antigens. The presence of HLA antigen/anti-HLA-antibody immune complexes in patients' sera was positively associated with chronic humoral rejection (P less than 0.0001). Patients who tolerated the graft in spite of having developed antibodies against one of its mismatched HLA antigens show specific antiidiotypic (anti-anti-HLA-antibodies). Such antiidiotypic antibodies were not found in sera from patients with chronic rejection (P = 0.005). This indicates that antiidiotypic antibodies may delay the progression of chronic humoral rejection.