Subclass-specific antibody responses to human cytomegalovirus in lung transplant recipients and their association with constant heavy immunoglobulin G chain polymorphism and virus replication

Human cytomegalovirus (HCMV) causes severe infections in transplant recipients. The significance of the HCMV-specific antibody (Ab) response in limiting HCMV replication is not clear. Therefore, we analyzed the HCMV-specific subclass Ab profile in lung transplant recipients (LTRs) and its association with the genomic immunoglobulin G (IgG) heavy-chain variants GM3/17 and HCMV DNAemia.We determined HCMV-specific total IgG, IgG1 and IgG3 Ab levels by enzyme-linked immunoassay and HCMV-DNAemia by quantitative polymerase chain reaction during post-transplant follow-up in 57 LTRs and, in 44 of these recipients, the genetic allotype marker 359a/g variants (reflecting GM3/17 allotypes) by genotyping.In seropositive LTRs there was a significant Ab response to HCMV viremia (p = 0.0005), especially when low HCMV DNA levels were detected (<1,000 copies/ml: p = 0.0012; DNAemia >1,000 copies/ml: p = 0.0516). In particular, IgG3 but not IgG1, increased with viremia (IgG3: p = 0.0004). IgG1 levels were significantly lower in patients with 359 g/g (GM3/3) than in those with 359 a/g (GM3/17) variant (p < 0.0001). Of note, the IgG3 increase with viremia occurred particularly in patients carrying the IgG1 low-level 359 g/g variant (p < 0.0002).These data suggest that the HCMV-specific Ab response, and especially the IgG3 subclass response, correlate significantly with HCMV replication after transplantation. The patients' GM 3/17 variant is significantly associated with their HCMV IgG subclass profile.