The mucosal immune system of the upper respiratory tract and recent progress in mucosal vaccines

Intramuscular mRNA BNT162b2 vaccine against SARS-CoV-2 induces robust neutralizing salivary IgA

“…The well-studied poliovirus case with the known difference between Inactivated Polio Vaccine (IPV) and Oral Polio Vaccine (OPV) exemplifies the importance of such mimicry for providing the sterilizing immunity (Hird and Grassly, 2012; Onorato et al, 1991). Many more recent studies also demonstrate that the mucosal route of vaccination provides such beneficial protection against respiratory and digestive-tract virus and bacterial infections, including influenza and rotavirus and even SARS-CoV-2 (Hamajima et al, 2002; Hellfritzsch and Scherließ, 2019; JONES et al, 2006; Kurono, 2021; Lapuente et al, 2021; Lavelle and Ward, 2021; Perrone et al, 2009; Terauchi et al, 2018; Yang and Varga, 2014). However, formulating immunogenic, broad, and safe ‘subunit’ or ‘inactivated’ mucosal viral vaccine, capable of eliciting long-term efficient and balanced mucosal- plus -systemic protections, remains challenging.…”

Hacking Commensal Bacteria to Consolidate the Adaptive Mucosal Immune Response in the Gut–Lung Axis: Future Possibilities for SARS-CoV-2 Protection

“…This is proven by literature reports that show mortality rates in infants in correlation to breastfeeding since it provides SIgA from the mother to the child and prevents infections in the gastrointestinal and respiratory tracts [ 20 , 33 ]. SIgA cannot kill microorganisms because it does not have bacteriolytic or complement activation effects, but it inhibits adherence of microorganisms to the epithelial cells by neutralizing and agglutinating activity [ 34 ]. In opposition, when IgG binds to the bacteria, the bacteria will be destroyed through lysis and complement activation.…”

“…Combining these systems, the SIgA can bind the bacteria, and the mucociliary system excretes it. IgG also plays a role in this tissue, and it is responsible for lysing the bacteria and complement activation [ 34 ]. The second nasal immunological barrier is composed of a network similar to the one found in the GIT, presenting microfold M cells, macrophages, innate lymphoid cells, dendritic cells, and B and T lymphocytes [ 34 , 69 ].…”

“…IgG also plays a role in this tissue, and it is responsible for lysing the bacteria and complement activation [ 34 ]. The second nasal immunological barrier is composed of a network similar to the one found in the GIT, presenting microfold M cells, macrophages, innate lymphoid cells, dendritic cells, and B and T lymphocytes [ 34 , 69 ]. Interestingly, the presence of bronchus-associated lymphoid tissue (and IgA-producing mucosal B cells) is more common in children and adolescents than adults, and that could be correlated to the fact that younger individuals present a milder case when infected with SARS-CoV-2 in comparison to older adults [ 70 , 71 ], showing how local immunization may be a good option to avoid the severity of COVID-19 cases.…”

“…In this sense, any colonizing species naturally present in the upper respiratory tract could be targeted to produce mucosal vaccines for the respiratory tract since it will elicit a lung response if it exceeds the average load observed there [ 34 , 73 ].…”