Persistence of Human Bocavirus 1 in Tonsillar Germinal Centers and Antibody-Dependent Enhancement of Infection

Abstract

Human bocavirus 1 (HBoV1), a nonenveloped single-stranded DNA parvovirus, causes mild to life-threatening respiratory tract infections, acute otitis media, and encephalitis in young children. HBoV1 often persists in nasopharyngeal secretions for months, hampering diagnosis. It has also been shown to persist in pediatric palatine and adenoid tonsils, which suggests that lymphoid organs are reservoirs for virus spread; however, the tissue site and host cells remain unknown. Our aim was to determine, in healthy nonviremic children with preexisting HBoV1 immunity, the adenotonsillar persistence site(s), host cell types, and virus activity. We discovered that HBoV1 DNA persists in lymphoid germinal centers (GCs), but not in the corresponding tonsillar epithelium, and that the cell types harboring the virus are mainly naive, activated, and memory B cells and monocytes. Both viral DNA strands and both sides of the genome were detected, as well as infrequent mRNA. Moreover, we showed, in B-cell and monocyte cultures and ex vivo tonsillar B cells, that the cellular uptake of HBoV1 occurs via the Fc receptor (FcγRII) through antibody-dependent enhancement (ADE). This resulted in viral mRNA transcription, known to occur exclusively from double-stranded DNA in the nucleus, however, with no detectable productive replication. Confocal imaging with fluorescent virus-like particles moreover disclosed endocytosis. To which extent the active HBoV1 GC persistence has a role in chronic inflammation or B-cell maturation disturbances, and whether the virus can be reactivated, will be interesting topics for forthcoming studies. IMPORTANCE Human bocavirus 1 (HBoV1), a common pediatric respiratory pathogen, can persist in airway secretions for months hampering diagnosis. It also persists in tonsils, providing potential reservoirs for airway shedding, with the exact location, host cell types, and virus activity unknown. Our study provides new insights into tonsillar HBoV1 persistence. We observed HBoV1 persistence exclusively in germinal centers where immune maturation occurs, and the main host cells were B cells and monocytes. In cultured cell lines and primary tonsillar B cells, we showed the virus uptake to be significantly enhanced by HBoV1-specific antibodies, mediated by the cellular IgG receptor, leading to viral mRNA synthesis, but without detectable productive replication. Possible implications of such active viral persistence could be tonsillar inflammation, disturbances in immune maturation, reactivation, or cell death with release of virus DNA, explaining the long-lasting HBoV1 airway shedding.

Human bocavirus-1 screening in infants with acute lower respiratory tract infection

“… 27 A study in Finland showed that HBoV persisted in the respiratory tract for long periods, increasing the chance of co-detection with other viruses. 28 Emanuels et al. also found a high prevalence of HBoV and other pathogens in Nepal.…”

Human bocavirus 1 respiratory tract reactivations or reinfections in two adults, contributing to neurological deficits and death

“…Mostly in children, but infrequently also in adults, HBoV1 DNA is able to persist in tonsils, which have been suggested to be reservoirs for virus spread. HBoV1 has been shown to localize in tonsillar germinal centres (GCs) and to invade GC B cells and monocytes through antibody-dependent enhancement (ADE) of infection via the Fc receptor [ 30 ]. More studies of the clinical significance of latency, OAS and ADE are much needed to clarify these interesting phenomena.…”

Prevalence, Cell Tropism, and Clinical Impact of Human Parvovirus Persistence in Adenomatous, Cancerous, Inflamed, and Healthy Intestinal Mucosa

“…The PCR products of target amplicons, spliced VP and non-spliced NS1, were cloned into pSTBlue vector and served as assay controls. RNA polymerase II (RPII), human housekeeping mRNA, was quantified for each RNA prep as internal control, as described ( Xu et al, 2021 ).…”

“…B19V DNA has been detected in various tissue types including synovium, skin, heart, liver, muscle, tonsil, testis, brain, salivary glands, bone, and bone marrow ( Cassinotti et al, 1997 ; Söderlund et al, 1997 ; Eis-Hübinger et al, 2001 ; Söderlund-Venermo et al, 2002 ; Vuorinen et al, 2002 ; Lotze et al, 2004 ; Hobbs, 2006 ; Norja et al, 2006 ; Manning et al, 2007 ; Adamson-Small et al, 2014 ; Toppinen et al, 2015a ; Pyöriä et al, 2017 ; Santonja et al, 2017 ), of both symptomatic and healthy individuals. HBoV DNAs have been detected in tonsils, intestine, and heart ( Kuethe et al, 2009 ; Kapoor et al, 2011 ; Proenca-Modena et al, 2012 ; Schildgen et al, 2013 ; Abdel-Moneim et al, 2016 ; Qiu et al, 2017 ; Ivaska et al, 2019 ; Xu et al, 2021 ). Associations of B19V or HBoV infection with inflammatory bowel diseases, such as ulcerative colitis (UC), or gastrointestinal tumors have been suggested, but the causative role has not been verified ( Li et al, 2007 ; Pironi et al, 2009 ; Schildgen et al, 2013 ; Abdel-Moneim et al, 2016 ).…”

“…In B19V-infected non-permissive cell cultures, VP and NS1 mRNAs may be expressed ( Zakrzewska et al, 2005 ; Ganaie and Qiu, 2018 ). In monocytes, endothelial cells, and both primary and immortalized B cells, the uptake of B19V has been shown to occur through antibody-dependent enhancement (ADE) via the Fc receptor or complement factor C1q ( Munakata et al, 2006 ; von Kietzell et al, 2014 ; Pyöriä et al, 2017 ), a mechanism initially shown for Aleutian mink disease virus and recently also for HBoV1 ( Kanno et al, 1993 ; Xu et al, 2021 ). The natural host cells for HBoVs are unknown, but HBoV1 is able to replicate and cause pathological changes in non-dividing polarized air-liquid cell cultures of human airway epithelia ( Huang et al, 2012 ).…”