BK virus antibody titers and intensity of infections after renal transplantation

Background: The mean urine BK viral load in kidney transplant recipients increases with the intensity of infection as the infection progresses from transient viruria to sustained viremia. Objectives: This study investigated whether the intensity of infection is associated with the humoral immune response. Study design: We measured BKV-specific IgG antibody titers in stored samples obtained serially over a 1-year period from 70 kidney transplant recipients with BKV infection and 17 control recipients without active BKV infection. Results: The mean pre-transplant BKV antibody level was lower in recipients who developed viremia than the mean level in those who never developed viremia (p = 0.004). Mean antibody titers in recipients who never showed evidence of active BKV infection rose slightly after transplant despite immunosuppression. The magnitude of the rise in the mean antibody titers in recipients who developed active BKV infection correlated with the intensity of infection (p < 0.001). Conclusions: The mean antibody level increased in accordance with the intensity of the infection post-transplant. Pre-transplant seropositivity did not protect against sustained viremia and the antibody response was not associated with clearance of the virus.