Serological cross-reactivities between antibodies to simian virus 40, BK virus, and JC virus assessed by virus-like-particle-based enzyme immunoassays

Abstract

Enzyme immunoassays (EIAs) for detection of serum antibodies to simian virus 40 (SV40), BK virus (BKV), and JC virus (JCV) were developed by using virus-like-particles (VLPs) produced in insect cells from recombinant baculoviruses expressing the VP1 protein of the respective virus. Rhesus macaque sera with neutralizing antibodies to SV40 showed a high level of reactivity in the SV40 VLP-based EIA, and these sera also showed lower levels of reactivity in the BKV and JCV VLP-based EIAs. Rhesus macaque sera negative for neutralizing antibodies to SV40 were negative in all three EIAs. Competitive binding assays showed that SV40 VLPs inhibited BKV reactivity. In rhesus macaque sera, high optical density (OD) values for antibodies to SV40 VLPs were correlated with high OD values for antibodies to BKV but not with high OD values for antibodies to JCV VLPs. Human sera with neutralizing antibodies to SV40 were more reactive to SV40 VLPs than human sera without neutralizing antibodies to SV40. The greater SV40 reactivities of human sera were correlated with greater reactivities to BKV VLPs but not JCV VLPs. These data suggest that cross-reactivity with BKV antibodies may account for part of the low-level SV40 reactivity seen in human sera. With their greater versatility and their suitability for large-scale testing, the VLP-based EIAs for SV40, BKV, and JCV are likely to contribute to a better understanding of the biology of these viruses.

FIG. 1.

SDS-PAGE of crude and purified SV40, BKV, and JCV VLPs (A) and transmission electron micrographs of SV40, BKV, and JCV VLPs (B). A lysate of insect cells infected with the respective VP1-expressing recombinant baculovirus (lane 2) or 5 μg of purified VLP protein (lane 3) was subjected to SDS-PAGE. Molecular weight markers (10³) are shown in lane 1. Electron micrographs of purified VLPs are shown at ×105,000 magnification. The bars correspond to 100 nm. The open arrow points to an empty particle, and the solid arrow points to a full particle.

FIG. 2.

Reactivities of SV40-neutralizing antibody-positive and -negative rhesus macaque sera in the SV40, BKV, and JCV VLP-based EIAs. Serum samples were tested for neutralizing antibodies in the SV40 plaque inhibition assay. The distributions of the 17 antibody-negative serum samples (A) and 39 antibody-positive serum samples (B) are shown. The length of each box corresponds to the interquartile range, with the upper boundary of the box representing the 75th percentile and lower boundary of the box representing the 25th percentile. The horizontal line in the box indicates the median value. The lines extending upward and downward from the box mark the 10th to 90th percentile range. Outlier values are shown as closed circles.

FIG. 3.

Percent blocking of SV40 VLP reactivities of 14 rhesus macaque serum samples by SV40 and BKV VLPs. Ten serum samples from SV40-seropositive rhesus macaques that were naturally infected (samples 1 to 10) and four serum samples from SV40-seropositive macaques that were infected by experimental inoculation (samples 11 to 14) were preincubated with 3 μg of either SV40 or BKV VLP protein per ml or buffer alone and added to an SV40-coated plate. Percent blocking was calculated as 1 − OD_{buffer alone}/OD_VLP.

FIG. 4.

Percent blocking of BKV VLP reactivities of 14 rhesus macaque serum samples by SV40 and BKV VLPs. Serum samples were tested on BKV-coated plates as described in the legend to Fig. 3.

FIG. 5.

Reactivities of human sera in the SV40, BKV, and JCV VLP-based EIAs. One hundred thirty serum samples were tested in the SV40 and BKV VLP-based EIAs, and 123 serum samples were tested in the JCV VLP-based EIA. See the legend to Fig. 2 for an explanation of the box plot diagrams.

FIG. 6.

Reactivities of human sera in the BKV VLP-based EIA by quartile of SV40 reactivity. The distribution of the BKV reactivities of 130 human serum samples is plotted by quartile of SV40 seroreactivity. See the legend to Fig. 2 for an explanation of the box plot diagrams.

FIG. 7.

Reactivities of 13 SV40-neutralizing antibody-positive and 115 antibody-negative human serum samples in the SV40 VLP-based EIA. Serum samples were tested for neutralizing antibodies in the SV40 plaque inhibition assay. See the legend to Fig. 2 for an explanation of the box plot diagrams.