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Continuous assessment of the impact of SARS-CoV-2 on the host at the cell-type level is crucial for understanding key mechanisms involved in host defense responses to viral infection. We investigated host response to ancestral-strain and Alpha-variant SARS-CoV-2 infections within air-liquid-interface human nasal epithelial cells from younger adults (26-32 Y) and older children (12-14 Y) using single-cell RNA-sequencing. Ciliated and secretory-ciliated cells formed the majority of highly infected cell-types, with the latter derived from ciliated lineages. Strong innate immune responses were observed across lowly infected and uninfected bystander cells and heightened in Alpha-infection. Alpha highly infected cells showed increased expression of protein-refolding genes compared with ancestral-strain-infected cells in children. Furthermore, oxidative phosphorylation-related genes were down-regulated in bystander cells versus infected and mock-control cells, underscoring the importance of these biological functions for viral replication. Overall, this study highlights the complexity of cell-type-, age- and viral strain-dependent host epithelial responses to SARS-CoV-2., Competing Interests: The authors declare no competing interests., (© 2024 The Authors.)

Background: SARS-CoV-2 booster vaccination should ideally enhance protection against variants and minimise immune imprinting. This Phase I trial evaluated two vaccines targeting SARS-CoV-2 beta-variant receptor-binding domain (RBD): a recombinant dimeric RBD-human IgG 1 F c -fusion protein, and an mRNA encoding a membrane-anchored RBD., Methods: 76 healthy adults aged 18-64 y, previously triple vaccinated with licensed SARS-CoV-2 vaccines, were randomised to receive a 4th dose of either an adjuvanted (MF59®, CSL Seqirus) protein vaccine (5, 15 or 45 μg, N = 32), mRNA vaccine (10, 20, or 50 μg, N = 32), or placebo (saline, N = 12) at least 90 days after a 3rd boost vaccination or SARS-CoV-2 infection. Bleeds occurred on days 1 (prior to vaccination), 8, and 29., Clinicaltrials: govNCT05272605., Findings: No vaccine-related serious or medically-attended adverse events occurred. The protein vaccine reactogenicity was mild, whereas the mRNA vaccine was moderately reactogenic at higher dose levels. Best anti-RBD antibody responses resulted from the higher doses of each vaccine. A similar pattern was seen with live virus neutralisation and surrogate, and pseudovirus neutralisation assays. Breadth of immune response was demonstrated against BA.5 and more recent omicron subvariants (XBB, XBB.1.5 and BQ.1.1). Binding antibody titres for both vaccines were comparable to those of a licensed bivalent mRNA vaccine. Both vaccines enhanced CD4 + and CD8 + T cell activation., Interpretation: There were no safety concerns and the reactogenicity profile was mild and similar to licensed SARS-CoV-2 vaccines. Both vaccines showed strong immune boosting against beta, ancestral and omicron strains., Funding: Australian Government Medical Research Future Fund, and philanthropies Jack Ma Foundation and IFM investors., Competing Interests: Declaration of interests The vaccines evaluated in this Phase I study were the result of independent University of Melbourne and Monash University research and development, with funding provided by the Australian Government's Medical Research Future Fund (MRFF), the National Health and Medical Research Council (NHMRC), the Victorian Government (mRNA Victoria) and philanthropic funders. The MF59 for the protein-RBD candidate was donated by CSL Seqirus. One author (S.R.) is an employee of CSL Seqirus and he also has an adjunct (honorary) appointment to the University of Melbourne. G.D., N.G., D.P., D.I.G. are named inventors on 2 provisional patents for the RBD-Fc dimer vaccine in this study. T.M.N. has been a DSMB member for vaccine studies conducted by Moderna, Clover, Novavax, CSL Seqirus, and SK Bioscience Korea, and has received payment for advisory roles on vaccines from AstraZeneca, Moderna, MSD, Sanofi, CSL, and Pfizer. G.D. received salary support from philanthropic funds from IFM Investors Pty Ltd. S.L. received consulting fees from several companies related to HIV research, and honoraria from MSD and Gilead. H.McQ. received consulting fees from Ena Respiratory Pty Ltd. K.S. was a member of a DSMB for a vaccine study in Thailand. H.alW. received consulting and research funding from CSL Seqirus. D.I.G. received research support from CSL., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

The diversity of COVID-19 disease in otherwise healthy people, from seemingly asymptomatic infection to severe life-threatening disease, is not clearly understood. We passaged a naturally occurring near-ancestral SARS-CoV-2 variant, capable of infecting wild-type mice, and identified viral genomic mutations coinciding with the acquisition of severe disease in young adult mice and lethality in aged animals. Transcriptomic analysis of lung tissues from mice with severe disease elucidated a host antiviral response dominated mainly by interferon and IL-6 pathway activation in young mice, while in aged animals, a fatal outcome was dominated by TNF and TGF-β signaling. Congruent with our pathway analysis, we showed that young TNF-deficient mice had mild disease compared to controls and aged TNF-deficient animals were more likely to survive infection. Emerging clinical correlates of disease are consistent with our preclinical studies, and our model may provide value in defining aberrant host responses that are causative of severe COVID-19.

Background: The SARS-CoV-2 global pandemic has fuelled the generation of vaccines at an unprecedented pace and scale. However, many challenges remain, including: the emergence of vaccine-resistant mutant viruses, vaccine stability during storage and transport, waning vaccine-induced immunity, and concerns about infrequent adverse events associated with existing vaccines., Methods: We report on a protein subunit vaccine comprising the receptor-binding domain (RBD) of the ancestral SARS-CoV-2 spike protein, dimerised with an immunoglobulin IgG1 Fc domain. These were tested in conjunction with three different adjuvants: a TLR2 agonist R4-Pam2Cys, an NKT cell agonist glycolipid α-Galactosylceramide, or MF59® squalene oil-in-water adjuvant, using mice, rats and hamsters. We also developed an RBD-human IgG1 Fc vaccine with an RBD sequence of the immuno-evasive beta variant (N501Y, E484K, K417N). These vaccines were also tested as a heterologous third dose booster in mice, following priming with whole spike vaccine., Findings: Each formulation of the RBD-Fc vaccines drove strong neutralising antibody (nAb) responses and provided durable and highly protective immunity against lower and upper airway infection in mouse models of COVID-19. The 'beta variant' RBD vaccine, combined with MF59® adjuvant, induced strong protection in mice against the beta strain as well as the ancestral strain. Furthermore, when used as a heterologous third dose booster, the RBD-Fc vaccines combined with MF59® increased titres of nAb against other variants including alpha, delta, delta+, gamma, lambda, mu, and omicron BA.1, BA.2 and BA.5., Interpretation: These results demonstrated that an RBD-Fc protein subunit/MF59® adjuvanted vaccine can induce high levels of broadly reactive nAbs, including when used as a booster following prior immunisation of mice with whole ancestral-strain spike vaccines. This vaccine platform offers a potential approach to augment some of the currently approved vaccines in the face of emerging variants of concern, and it has now entered a phase I clinical trial., Funding: This work was supported by grants from the Medical Research Future Fund (MRFF) (2005846), The Jack Ma Foundation, National Health and Medical Research Council of Australia (NHMRC; 1113293) and Singapore National Medical Research Council (MOH-COVID19RF-003). Individual researchers were supported by an NHMRC Senior Principal Research Fellowship (1117766), NHMRC Investigator Awards (2008913 and 1173871), Australian Research Council Discovery Early Career Research Award (ARC DECRA; DE210100705) and philanthropic awards from IFM investors and the A2 Milk Company., Competing Interests: Declaration of interests Two provisional patents (PCT/AU2021/051553 and PCT/AU2023/050093) covering the RBD-Fc vaccines described in this study, and underlying technology, have been submitted through The University of Melbourne, with D.I.G., G.D., N.A.G., D.C.J. and D.F.J.P. as co-inventors. C.W.T. and L.-f.W. are co-inventors of a patent on the surrogate virus neutralization test (sVNT) platform. S.R.L. receives consulting fees from ViiV, Vaxxinity, Esfam, Abbvie, and Gilead. S.R.L. has received honoraria from Merck, Sharpe and Dohme, and from Gilead. K.S. is on a DSMB for a vaccine study in Thailand, and is Chair of the WHO Technical Advisory Group on COVID-19 vaccines (TAG-CO-VAC). T.N. receives research contracts to conduct clinical trials, with funding to institution from Moderna, SanofiPasteur, GSK, Iliad Biotechnologies, Dynavax, Seqirus, Janssen, MSD. T.N. receives consulting fees from GSK, Seqirus, MSD, SanofiPasteur, AstraZeneca, Moderna, BioNet, Pfizer. T.N. serves on DSMBs for Seqirus, Clover, Moderna, Emergent, Serum Institute of India, SK Bioscience Korea, Emergent Biosolutions, Novavax. S.R. is an employee of CSL Seqirus that is a maker of influenza vaccines. D.C.J. is a founder and shareholder of Ena Respiratory. C.Y.W. and W.Z. are shareholders of Ena Respiratory. D.I.G. has received research funding from CSL for an unrelated project. All other authors declare no conflict of interests., (Copyright © 2023. Published by Elsevier B.V.)

The development of therapeutics to prevent or treat COVID-19 remains an area of intense focus. Protein biologics, including monoclonal antibodies and nanobodies that neutralize virus, have potential for the treatment of active disease. Here, we have used yeast display of a synthetic nanobody library to isolate nanobodies that bind the receptor-binding domain (RBD) of SARS-CoV-2 and neutralize the virus. We show that combining two clones with distinct binding epitopes within the RBD into a single protein construct to generate biparatopic reagents dramatically enhances their neutralizing capacity. Furthermore, the biparatopic nanobodies exhibit enhanced control over clinically relevant RBD variants that escaped recognition by the individual nanobodies. Structural analysis of biparatopic binding to spike (S) protein revealed a unique binding mode whereby the two nanobody paratopes bridge RBDs encoded by distinct S trimers. Accordingly, biparatopic nanobodies offer a way to rapidly generate powerful viral neutralizers with enhanced ability to control viral escape mutants., Competing Interests: Lin-Fa Wang and Chee Wah Tan are co-inventors of the surrogate virus neutralization test commercialized under the tradename cPass by GenScript Biotech., (© 2022 The Author(s).)

The global urgency to uncover medical countermeasures to combat the COVID-19 pandemic caused by the severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) has revealed an unmet need for robust tissue culture models that faithfully recapitulate key features of human tissues and disease. Infection of the nose is considered the dominant initial site for SARS-CoV-2 infection and models that replicate this entry portal offer the greatest potential for examining and demonstrating the effectiveness of countermeasures designed to prevent or manage this highly communicable disease. Here, we test an air-liquid-interface (ALI) differentiated human nasal epithelium (HNE) culture system as a model of authentic SARS-CoV-2 infection. Progenitor cells (basal cells) were isolated from nasal turbinate brushings, expanded under conditionally reprogrammed cell (CRC) culture conditions and differentiated at ALI. Differentiated cells were inoculated with different SARS-CoV-2 clinical isolates. Infectious virus release into apical washes was determined by TCID 50 , while infected cells were visualized by immunofluorescence and confocal microscopy. We demonstrate robust, reproducible SARS-CoV-2 infection of ALI-HNE established from different donors. Viral entry and release occurred from the apical surface, and infection was primarily observed in ciliated cells. In contrast to the ancestral clinical isolate, the Delta variant caused considerable cell damage. Successful establishment of ALI-HNE is donor dependent. ALI-HNE recapitulate key features of human SARS-CoV-2 infection of the nose and can serve as a pre-clinical model without the need for invasive collection of human respiratory tissue samples.

Background: As vaccines against SARS-CoV-2 are now being rolled out, a better understanding of immunity to the virus, whether from infection, or passive or active immunisation, and the durability of this protection is required. This will benefit from the ability to measure antibody-based protection to SARS-CoV-2, ideally with rapid turnaround and without the need for laboratory-based testing., Methods: We have developed a lateral flow POC test that can measure levels of RBD-ACE2 neutralising antibody (NAb) from whole blood, with a result that can be determined by eye or quantitatively on a small instrument. We compared our lateral flow test with the gold-standard microneutralisation assay, using samples from convalescent and vaccinated donors, as well as immunised macaques., Findings: We show a high correlation between our lateral flow test with conventional neutralisation and that this test is applicable with animal samples. We also show that this assay is readily adaptable to test for protection to newly emerging SARS-CoV-2 variants, including the beta variant which revealed a marked reduction in NAb activity. Lastly, using a cohort of vaccinated humans, we demonstrate that our whole-blood test correlates closely with microneutralisation assay data (specificity 100% and sensitivity 96% at a microneutralisation cutoff of 1:40) and that fingerprick whole blood samples are sufficient for this test., Interpretation: Taken together, the COVID-19 NAb-test TM device described here provides a rapid readout of NAb based protection to SARS-CoV-2 at the point of care., Funding: Support was received from the Victorian Operational Infrastructure Support Program and the Australian Government Department of Health. This work was supported by grants from the Department of Health and Human Services of the Victorian State Government; the ARC (CE140100011, CE140100036), the NHMRC (1113293, 2002317 and 1116530), and Medical Research Future Fund Awards (2005544, 2002073, 2002132). Individual researchers were supported by an NHMRC Emerging Leadership Level 1 Investigator Grants (1194036), NHMRC APPRISE Research Fellowship (1116530), NHMRC Leadership Investigator Grant (1173871), NHMRC Principal Research Fellowship (1137285), NHMRC Investigator Grants (1177174 and 1174555) and NHMRC Senior Principal Research Fellowships (1117766 and 1136322). Grateful support was also received from the A2 Milk Company and the Jack Ma Foundation., Competing Interests: Declaration of Competing Interest A provisional patent covering the COVID-19 NAb-test(TM) test and underlying technology has been submitted through The University of Melbourne. Dr. Fulford reports a patent Australian Provisional Patent Application 2021901011 (filed 7 April 2021) “Point of care lateral flow test for COVID19 detection” pending. Mr. Van reports grants from Government of the State of Victoria, during the conduct of the study; In addition, Mr. Van has a patent Australian Provisional Patent Application 2021901011 (filed 7 April 2021) “Point of care lateral flow test for COVID19 detection” pending. Dr. Gherardin reports a patent Australian Provisional Patent Application 2021901011 (filed 7 April 2021) “Point of care lateral flow test for COVID19 detection” pending. Ms. Zheng reports grants from Government of the State of Victoria, during the conduct of the study; In addition, Ms. Zheng has a patent Australian Provisional Patent Application 2021901011 (filed 7 April 2021) “Point of care lateral flow test for COVID19 detection” pending. Mr. Ciula has nothing to disclose. Prof. Drummer has nothing to disclose. Mr. Redmond has nothing to disclose. Dr. Tan has nothing to disclose. Ms. Boo has nothing to disclose. Dr. Center has nothing to disclose. Dr. Li has nothing to disclose. Dr. Grimley has nothing to disclose. Dr. Wines reports grants from Australian Govt, Medical Research Future Fund, grants from NHMRC, National Health and Medical Research Council GNT1145303, Australia, during the conduct of the study; In addition, Dr. Wines has a patent drafted for use of ACE2-Fc pending. Dr. Nguyen has nothing to disclose. Ms. Mordant has nothing to disclose. Dr. Ellenberg has nothing to disclose. Dr. Rowntree has nothing to disclose. Lukasz Kedzierski has nothing to disclose. Prof. Cheng reports that he is a member of government advisory committees advising on COVID policy. Prof. Doolan has nothing to disclose. Prof. Matthews reports grants from Curran Foundation, during the conduct of the study; grants from Gilead sciences, grants from Abbvie Inc outside the submitted work. Dr. Bond has nothing to disclose. Prof. Hogarth reports grants from NHMRC, grants from MRFF, during the conduct of the study; In addition, Prof. Hogarth has a patent Antiviral pending. A/Prof. McQuilten reports grants from Medical Research Future Fund, during the conduct of the study. Prof. Subbarao has nothing to disclose. Prof. Kedzierska has nothing to disclose. Dr. Juno has nothing to disclose. Dr. Wheatley has nothing to disclose. Prof. Kent has nothing to disclose. Prof. Williamson has nothing to disclose. Prof. Purcell reports grants from Victorian Government DHHS, grants from Medical Research Future Fund, other from Jack Ma Foundation, during the conduct of the study; In addition, Prof. Purcell has a patent PCT/AU2021/050839 pending. Prof. Anderson reports grants from Government of the State of Victoria, during the conduct of the study; other from Nanjing BioPoint Diagnostic Technology, outside the submitted work; In addition, Prof. Anderson has a patent Australian Provisional Patent Application 2021901011 (filed 7 April 2021) “Point of care lateral flow test for COVID19 detection” pending. Prof. Godfrey reports grants from Victorian Government DHHS, and from Australian Research Council, during the conduct of the study; grants from Medical Research Future Fund, other from Jack Ma Foundation, grants from National Health and Medical Research Council, outside the submitted work; In addition, Prof. Godfrey has a patent Australian Provisional Patent Application 2021901011 (filed 7 April 2021) “Point of care lateral flow test for COVID19 detection” pending., (Copyright © 2021. Published by Elsevier B.V.)

The SARS-CoV-2 receptor binding domain (RBD) is both the principal target of neutralizing antibodies and one of the most rapidly evolving domains, which can result in the emergence of immune escape mutations, limiting the effectiveness of vaccines and antibody therapeutics. To facilitate surveillance, we developed a rapid, high-throughput, multiplex assay able to assess the inhibitory response of antibodies to 24 RBD natural variants simultaneously. We demonstrate how this assay can be implemented as a rapid surrogate assay for functional cell-based serological methods to measure the SARS-CoV-2 neutralizing capacity of antibodies at the angiotensin-converting enzyme 2-RBD (ACE2-RBD) interface. We describe the enhanced affinity of RBD variants N439K, S477N, Q493L, S494P, and N501Y to the ACE2 receptor and demonstrate the ability of this assay to bridge a major gap for SARS-CoV-2 research, informing selection of complementary monoclonal antibody candidates and the rapid identification of immune escape to emerging RBD variants following vaccination or natural infection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in an unprecedented need for diagnostic testing that is critical in controlling the spread of COVID-19. We propose a portable infrared spectrometer with purpose-built transflection accessory for rapid point-of-care detection of COVID-19 markers in saliva. Initially, purified virion particles were characterized with Raman spectroscopy, synchrotron infrared (IR) and AFM-IR. A data set comprising 171 transflection infrared spectra from 29 subjects testing positive for SARS-CoV-2 by RT-qPCR and 28 testing negative, was modeled using Monte Carlo Double Cross Validation with 50 randomized test and model sets. The testing sensitivity was 93 % (27/29) with a specificity of 82 % (23/28) that included positive samples on the limit of detection for RT-qPCR. Herein, we demonstrate a proof-of-concept high throughput infrared COVID-19 test that is rapid, inexpensive, portable and utilizes sample self-collection thus minimizing the risk to healthcare workers and ideally suited to mass screening., (© 2021 Wiley-VCH GmbH.)

Inducing humoral, cellular and mucosal immunity is likely to improve the effectiveness of HIV-1 vaccine strategies. Here, we tested a vaccine regimen in pigtail macaques using an intranasal (i.n.) recombinant Fowl Pox Virus (FPV)-gag pol env-IL-4R antagonist prime, intramuscular (i.m.) recombinant Modified Vaccinia Ankara Virus (MVA)-gag pol-IL-4R antagonist boost followed by an i.m SOSIP-gp140 boost. The viral vector-expressed IL-4R antagonist transiently inhibited IL-4/IL-13 signalling at the vaccination site. The SOSIP booster not only induced gp140-specific IgG, ADCC (antibody-dependent cellular cytotoxicity) and some neutralisation activity, but also bolstered the HIV-specific cellular and humoral responses. Specifically, superior sustained systemic and mucosal HIV Gag-specific poly-functional/cytotoxic CD4 + and CD8 + T cells were detected with the IL-4R antagonist adjuvanted strategy compared to the unadjuvanted control. In the systemic compartment elevated Granzyme K expression was linked to CD4 + T cells, whilst Granzyme B/TIA-1 to CD8 + T cells. In contrast, the cytotoxic marker expression by mucosal CD4 + and CD8 + T cells differed according to the mucosal compartment. This vector-based mucosal IL-4R antagonist/SOSIP booster strategy, which promotes cytotoxic mucosal CD4 + T cells at the first line of defence, and cytotoxic CD4 + and CD8 + T cells plus functional antibodies in the blood, may prove valuable in combating mucosal infection with HIV-1 and warrants further investigation.

The extensive glycosylation of HIV-1 envelope (Env) glycoprotein leaves few glycan-free holes large enough to admit broadly neutralizing antibodies (bnAb). Consequently, most bnAbs must inevitably make some glycan contacts and avoid clashes with others. To investigate how Env glycan maturation regulates HIV sensitivity to bnAbs, we modified HIV-1 pseudovirus (PV) using various glycoengineering (GE) tools. Promoting the maturation of α-2,6 sialic acid (SA) glycan termini increased PV sensitivity to two bnAbs that target the V2 apex and one to the interface between Env surface gp120 and transmembrane gp41 subunits, typically by up to 30-fold. These effects were reversible by incubating PV with neuraminidase. The same bnAbs were unusually potent against PBMC-produced HIV-1, suggesting similar α-2,6 hypersialylated glycan termini may occur naturally. Overexpressing β-galactosyltransferase during PV production replaced complex glycans with hybrid glycans, effectively 'thinning' trimer glycan coverage. This increased PV sensitivity to some bnAbs but ablated sensitivity to one bnAb that depends on complex glycans. Other bnAbs preferred small glycans or galactose termini. For some bnAbs, the effects of GE were strain-specific, suggesting that GE had context-dependent effects on glycan clashes. GE was also able to increase the percent maximum neutralization (i.e. saturation) by some bnAbs. Indeed, some bnAb-resistant strains became highly sensitive with GE-thus uncovering previously unknown bnAb breadth. As might be expected, the activities of bnAbs that recognize glycan-deficient or invariant oligomannose epitopes were largely unaffected by GE. Non-neutralizing antibodies were also unaffected by GE, suggesting that trimers remain compact. Unlike mature bnAbs, germline-reverted bnAbs avoided or were indifferent to glycans, suggesting that glycan contacts are acquired as bnAbs mature. Together, our results suggest that glycovariation can greatly impact neutralization and that knowledge of the optimal Env glycoforms recognized by bnAbs may assist rational vaccine design.

Previously, VLPs bearing JR-FL strain HIV-1 Envelope trimers elicited potent neutralizing antibodies (nAbs) in 2/8 rabbits (PLoS Pathog 11(5): e1004932) by taking advantage of a naturally absent glycan at position 197 that borders the CD4 binding site (CD4bs). In new immunizations, we attempted to improve nAb responses by removing the N362 glycan that also lines the CD4bs. All 4 rabbits developed nAbs. One targeted the N197 glycan hole like our previous sera. Two sera depended on the N463 glycan, again suggesting CD4bs overlap. Heterologous boosts appeared to reduce nAb clashes with the N362 glycan. The fourth serum targeted a N362 glycan-sensitive epitope. VLP manufacture challenges prevented us from immunizing larger rabbit numbers to empower a robust statistical analysis. Nevertheless, trends suggest that targeted glycan removal may improve nAb induction by exposing new epitopes and that it may be possible to modify nAb specificity using rational heterologous boosts., (Copyright © 2017 Elsevier Inc. All rights reserved.)

There is now an overwhelming body of evidence that implicates bats in the dissemination of a long list of emerging and re-emerging viral agents, often causing illnesses or death in both animals and humans. Despite this, there is a paucity of information regarding the immunological mechanisms by which bats coexist with highly pathogenic viruses. Immunoglobulins are major components of the adaptive immune system. Early studies found bats may have quantitatively lower antibody responses to model antigens compared to conventional laboratory animals. To further understand the antibody response of bats, the present study purified and characterised the major immunoglobulin classes from healthy black flying foxes, Pteropus alecto. We employed a novel strategy, where IgG was initially purified and used to generate anti-Fab specific antibodies. Immobilised anti-Fab specific antibodies were then used to capture other immunoglobulins from IgG depleted serum. While high quantities of IgM were successfully isolated from serum, IgA was not. Only trace quantities of IgA were detected in the serum by mass spectrometry. Immobilised ligands specific to IgA (Jacalin, Peptide M and staphylococcal superantigen-like protein) also failed to capture P. alecto IgA from serum. IgM was the second most abundant serum antibody after IgG. A survey of mucosal secretions found IgG was the dominant antibody class rather than IgA. Our study demonstrates healthy P. alecto bats have markedly less serum IgA than expected. Higher quantities of IgG in mucosal secretions may be compensation for this low abundance or lack of IgA. Knowledge and reagents developed within this study can be used in the future to examine class-specific antibody response within this important viral host.