Both natural influenza infection and current seasonal influenza vaccines primarily induce neutralizing antibody responses against highly diverse epitopes within the “head” of the viral hemagglutinin (HA) protein. There is increasing interest in redirecting immunity toward the more conserved HA stem or stalk as a means of broadening protective antibody responses. Here we examined HA stem–specific B cell and T follicular helper (Tfh) cell responses in the context of influenza infection and immunization in mouse and monkey models. We found that during infection, the stem domain was immunologically subdominant to the head in terms of serum antibody production and antigen-specific B and Tfh cell responses. Similarly, we found that HA stem immunogens were poorly immunogenic compared with the full-length HA with abolished sialic acid binding activity, with limiting Tfh cell elicitation a potential constraint to the induction or boosting of anti-stem immunity by vaccination. Finally, we confirm that currently licensed seasonal influenza vaccines can boost preexisting memory responses against the HA stem in humans. An increased understanding of the immune dynamics surrounding the HA stem is essential to inform the design of next-generation influenza vaccines for broad and durable protection.

Influenza Other Respi Viruses. 2019;13:535-546. | 535 wileyonlinelibrary.com/journal/irv 1 | INTRODUC TI ON Animal models have proved critical in developing concepts of immunity to infection. Non-human primates (NHP) are a highly humanrelevant disease model for infectious agents due to high genetic conservation between humans and NHP. 1-3 However, significant cost and ethical issues often necessitate the use of smaller animal models for both basic and translational research. Mice (Mus musculus) are a favoured small animal model due to widespread availability, incisive transgenic models, comprehensive genomic information 4 and readily available reagents. However, for many viruses, alternative animal models better recapitulate human physiology and disease. Ferrets (Mustela putorius furo) have been employed to study the pathogenesis of a variety of human pathogens, including human and avian influenzas, coronaviruses including severe acute respiratory syndrome (SARS-CoV), 5-14 human respiratory syncytial virus (HRSV), 15-20 human metapneumovirus (HMPV), 21 Ebola virus 22-28 and henipavirus (Nipah virus and Hendra virus). 29-34 While ferretscan be productively infected with many of these viruses, a lack of some tools to interrogate ferret immunological responses to infection limits insights that might impact the development of vaccines and/or therapeutics. Here, we review recent insights gained from ferret models of human respiratory diseases, with a major focus on influenza, and highlight several knowledge gaps whose closure will greatly enhance the informational gain from ferret models to advance development of human vaccines and therapeutics. AbstractFerrets are a well-established model for studying both the pathogenesis and transmission of human respiratory viruses and evaluation of antiviral vaccines. Advanced immunological studies would add substantial value to the ferret models of disease but are hindered by the low number of ferret-reactive reagents available for flow cytometry and immunohistochemistry. Nevertheless, progress has been made to understand immune responses in the ferret model with a limited set of ferret-specific reagents and assays. This review examines current immunological insights gained from the ferret model across relevant human respiratory diseases, with a focus on influenza viruses. We highlight key knowledge gaps that need to be bridged to advance the utility of ferrets for immunological studies. K E Y W O R D S ferret, immunology, influenza How to cite this article: Wong J, Layton D, Wheatley AK, Kent SJ. Improving immunological insights into the ferret model of human viral infectious disease. Influenza Other Respi Viruses. 2019;13:535-546. https ://doi.

Hereford cattle were immunized with membranes and soluble components extracted from the midgut of Boophilus microplus. Membrane vaccines protected cattle (91%) against challenge with 3 x 20,000 larval ticks administered at intervals of 7 days. Vaccines made from soluble antigens did not protect cattle. Antibody levels measured by enzyme-linked immunosorbent assay (ELISA) related to the levels of protection induced by vaccination.