High prevalence of antibodies against polyomavirus WU, polyomavirus KI, and human bocavirus in German blood donors

Abstract

Background: DNA of the polyomaviruses WU (WUPyV) and KI (KIPyV) and of human bocavirus (HBoV) has been detected with varying frequency in respiratory tract samples of children. However, only little is known about the humoral immune response against these viruses. Our aim was to establish virus-specific serological assays and to determine the prevalence of immunoglobulin G (IgG) against these three viruses in the general population.

Methods: The capsid proteins VP1 of WUPyV and KIPyV and VP2 of HBoV were cloned into baculovirus vectors and expressed in Sf9 insect cells. IgG antibodies against WUPyV VP1, KIPyV VP1, and HBoV VP2 were determined by immunofluorescence assays in 100 plasma samples of blood donors.

Results: The median age of the blood donors was 31 years (range 20 - 66 yrs), 52% were male. 89% of the samples were positive for WUPyV IgG (median age 31 yrs, 49.4% male), 67% were positive for KIPyV IgG (median age 32 yrs, 46.3% male), and 76% were positive for HBoV IgG (median age 32 yrs, 51.3% male). For WUPyV and HBoV, there were no significant differences of the seropositivity rates with respect to age groups or gender. For KIPyV, the seropositivity rate increased significantly from 59% in the age group 20 - 29 years to 100% in the age group > 50 years.

Conclusions: High prevalences of antibodies against WUPyV, KIPyV, and HBoV were found in plasma samples of healthy adults. The results indicate that primary infection with these viruses occurs during childhood or youth. For KIPyV, the seropositivity appears to increase further during adulthood.

Figure 1

Confirmation of expression of recombinant proteins. Sf9 cells were infected with recombinant baculoviruses BacWUVP1, BacKIVP1, and BacBoVP2. Uninfected Sf9 cells served as negative control. After SDS-PAGE and immunoblot, proteins were visualised by staining with anti-V5 antibody. The expected protein sizes are ~46 kDa (WUPyV and KIPyV VP1) and ~66 kDa (HBoV VP2).

Figure 2

IFA for the detection of IgG antibodies against WUPyV VP1, KIPyV VP1, and HBoV VP2. Sf9 cells infected with recombinant baculoviruses were incubated with plasma samples of healthy blood donors. Bound antibodies were visualised with FITC-labelled anti-human IgG. Representative examples of positive and negative plasma samples are shown for each of the three antigens.

Figure 3

Age distribution of virus-specific IgG antibodies. The seroprevalence for WUPyV and HBoV did not differ significantly between age groups (p = 0.855 and p = 0.175, respectively). For KIPyV, a significant rise of seroprevalence rates was observed with increasing age (p = 0.026).