BK antibody and virus-specific IgM responses in renal transplant recipients, patients with malignant disease, and healthy people.

Haemagglutination-inhibition (HAI) antibodies to BK virus, including BK-virus-specific IgM, were determined before and after renal transplantation in 20 patients, in 57 patients with malignant disease, and in 66 healthy controls, Before transplantation 11 of the renal transplant recipients were seronegative, but eight later serocconverted, two before and six after transplantation. Twenty of the patients with malignant disease and 22 controls were also seronegative. The geometric mean titre of BK HAI antibodies was significantly higher among transplanted patients (1/180) than among controls (1/90). BK-virus-specific IgM antibody was detected in seven renal transplant recipients, six patients with malignant disease, and 13 healthy controls. In transplant recipients BK-virus-specific IgM antibody usually persisted throughout the duration of the study, and studies on controls from whom second serum samples were available suggested that they too had persistent BK-virus-specific IgM responses. The geometric mean titre of BK-virus-specific IgM HAI antibody was significantly greater in post-transplantation sera (1/223) than in control sera (1/28). The specificity of the detection of BK-virus-specific IgM HAI antibody was confirmed by direct visualisation of antibody by immune electron microscopy. The persistence of BK-virus-specific IgM suggested that BK virus continued to provide an antigenic stimulus. Nevertheless, there was no obvious association between the serological findings and any clinical features, and prospective studies will be needed to elucidate any such association.