Antibody Responses to Recombinant Polyomavirus BK Large T and VP1 Proteins in Young Kidney Transplant Patients

Abstract

BK virus (BKV)-specific immunity is critical for polyomavirus-associated nephropathy, but antibody responses are incompletely defined. We compared the hemagglutination inhibition assay (HIA) with immunoglobulin G enzyme immunoassays (EIA) to BKV proteins expressed in baculovirus-infected insect cells. N-terminal, internal, and C-terminal domains of the BKV large T antigen (BKLT) were fused to glutathione S-transferase (GST), yielding GST-BKLTD1, GST-BKLTD2, and GST-BKLTD3, respectively. The BKV capsid VP1 was expressed as a GST fusion (BKVP1) or as a native VP1 assembled into viruslike particles (BKVLP). We tested 422 sera from 28 healthy donors (HD), 99 dialysis patients (DP; median age, 15 years; range, 3 to 32 years), and 46 age-matched kidney transplant patients (KTP; median age, 15 years; range, 2 to 33 years). In HD, HIA and BKVLP EIA both yielded a 91.7% seroreactivity, whereas all other EIA responses were lower (BKVP1, 83.3%; BKLTD1, 25%; BKLTD2, 29%; BKLTD3, 40%). HIA titers significantly correlated with EIA levels for BKVLP, BKVP1, and BKLTD1 but not for BKLTD2 or BKLTD3, which were barely above the cutoff. In DP, the seroreactivities of HIA, BKVLP, and BKLTD1 were lower than that in HD (63.6%, 86.9%, and 10.1%, respectively) and they had lower titers (P < 0.001). In KTP, seropositivities for BKVLP, BKVP1, and BKLTD1 were 78%, 50%, and 17%, respectively, but anti-BKVLP levels increased significantly in KTP with viruria and viremia, whereas anti-BKLTD1 levels increased after clearing sustained BKV viremia. In conclusion, anti-BKVLP is equivalent to HIA in HD but is more sensitive to determine the BKV serostatus in DP and KTP. In KTP, anti-BKVLP responds to recent BKV viruria and viremia, whereas anti-BKLTD1 may indicate emerging BKV-specific immune control.Polyomaviruses (PyV) have been identified in many vertebrates; the main species found in humans are BK virus (BKV) and JC virus (C. Büchen-Osmond, Polyomaviridae, International Committee on Taxonomy of Viruses Database [www .ncbi.nlm.nih.gov/ICTVdb/]). PyV are small nonenveloped double-stranded DNA viruses with icosahedral particles of ϳ42 nm in diameter and are resistant to environmental inactivation (8, 31, 32; www.ncbi.nlm.nih.gov/ICTVdb/). The genome organization of the 5.1-kb circular genome is largely conserved and encodes six major proteins (20, 31, 32). The nuclear large tumor (LT) antigen and cytoplasmic small T antigen are expressed early in the viral life cycle, followed by the late cytoplasmic agnoprotein and the capsid proteins VP1, VP2, and VP3, which are transported into the nucleus for virion assembly (31,32,44). LT is a multifunctional regulatory protein with distinct domains (45,49). PyV capsids are formed by the assembly of 72 VP1 pentamers into a Tϭ7d icosahedral lattice associating with VP2 and VP3 and the circular viral genome (11,35,39).Seroprevalence data indicate that 50 to 90% of the general population has been exposed to BKV and JC virus (25,33,47).Both viruses persist in the renourinary tract as the principal site of latenc...

Human Merkel cell polyomavirus: virological background and clinical implications

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Phenotypic and Functional Characterization of Circulating Polyomavirus BK VP1-Specific CD8 + T Cells in Healthy Adults

“…LTAg is a nonstructural protein that is expressed only during the early phase of viral replication and during nonpermissive infection (1). The dominance of VP1-specific T cells over LTAg-specific T cells is in line with LTAg-specific antibody serum titers being lower than VP1-specific antibody titers (34,35). The discrepancy between VP1 and LTAg expression during the viral replication cycle and, as such, the variations in antigen exposure could explain the differences in population size of VP1-specific and LTAg-specific T cells.…”

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