Characterization of antibody response to human cytomegalovirus in Indian renal transplant patients

Background & objectives Cytomegalovirus (CMV) disease in seroendemic transp lant populations is due to reactivation of the virus, or reinfection. In th is context, the antibody response is likely to influence presentation, clin ical severity and outcome of the disease, and may provide a diagnostic and prognostic marker. This study was carried out in Indian renal transplant pa tients and healthy adults to characterize the antibody response to cytomega lovirus. Methods: Thirty three transplant recipients with CMV illness (symptomatolog y with IgM and/or nPCR positive status), 20 recipients who were asymptomati c in the 6 months of follow up after transplantation and 62 healthy control s were investigated for markers of CMV infection. These individuals were te sted for IgG avidity and neutralizing antibody by ELISA techniques. Results: All 53 transplant recipients were found to have an IgG avidity ind ex of > 50 per cent. Antibody to a CMV envelope glycoprotein gB/AD-1 (putat ive neutralizing antibody) was expressed as S/N ratio and was greater than or equal to5 in asymptomatic (65%) and symptomatic (27%) immunosuppressed r enal transplant recipients. However, none of the 53 CMV IgG positive health y controls were positive for neutralizing antibodies S/N ratio greater than or equal to5 (S/N ratio = sample mean OD/mean OD of 3 negative controls in each run). We observed the simultaneous presence of CMV PCR signal in leuk ocytes and neutralizing antibody (S/N ratio greater than or equal to5) in t he plasma in 22 (41.5%) of the 53 renal transplant recipients. Interpretation & conclusions: In this study among the immunosuppressed tran splant patients we observed an association between symptomatic disease and the relative absence of neutralizing antibodies. The neutralizing antibodie s are less frequently demonstrable among controls; while appearance in a hi gher proportion of asymptomatic recipients especially in association with h igh IgG avidity (> 90%) is suggestive of its role in control of CMV disease despite reactivation as evidenced by DNAemia while on immunosuppressive th erapy.