Respiratory Mucosal Immunity: Kinetics of Secretory Immunoglobulin A in Sputum and Throat Swabs From COVID-19 Patients and Vaccine Recipients

Bacterial lysates in modifying sIgA levels in the upper respiratory tract in COVID-19 patients

A great deal of evidence has accumulated suggesting an important role of mucosal immunity not only in preventing COVID-19 but also in the pathogenesis of this infection. The aim of the study was to evaluate the levels of secretory immunoglobulin A (sIgA) in different compartments of the upper respiratory tract in COVID-19 patients in relation to the severity of the disease and treatment with a bacteria-based immunomodulating agent (Immunovac VP4). The titers of sIgA were determined by ELISA in nasal epithelial swabs, pharyngeal swabs, and salivary gland secretions at baseline and on days 14 and 30 of treatment. The levels of nasal, pharyngeal and salivary sIgA were significantly lower in more severe patients (subgroup A) than in less severe patients (subgroup B), p < 0.01. In subgroup A, the patients who received Immunovac VP4 had higher pharyngeal sIgA levels in convalescent period than those who did not receive the therapy p < 0.05. In subgroup B patients, an increase in immunoglobulin levels was observed from baseline to day 14 of treatment whether they received the add-on therapy or not, p < 0.01. On day 30 of treatment, the sIgA levels in the standard treatment group, however, decreased, while the patients receiving the immunomodulating agent maintained high sIgA levels, p < 0.05. Oxygen saturation significantly increased by day 14 in both groups, p < 0.001. However, it was higher in the Immunovac VP4 group than in the standard treatment group, p < 0.01. Thus, addition of a bacterial lysate-based immunomodulating agent to the treatment regimen for moderate-to-severe COVID-19 induces the production of pharyngeal and salivary sIgA. SIgA production is inversely correlated to CRP levels and percentage of lung involvement on CT scan and is directly correlated to SpO2 levels.

Retinoic acid-adjuvanted vaccine induces antigen-specific secretory IgA in the gut of newborn piglets

Mucosal secretory IgA (SIgA) produced by subepithelial plasma cells in the lamina propria is the major antigen-specific defense mechanism against mucosal infections. We investigated if a retinoic acid (RA)-containing adjuvant in parenteral immunization, can induce vaccine-specific SIgA in the jejunal lumen in a dose-dependent manner in neonatal pigs immunized with a Chlamydia hybrid antigen. To accurately quantify SIgA responses in mucosal secretions, an antigen-specific ELISA method with secondary detection of porcine secretory component rather than IgA was developed. RA facilitated a stronger (or faster) IgG, IgA, IgM and SIgA response in serum after primary immunization, and a more than 10-fold significantly increased level of vaccine-specific SIgA in jejunum at termination 2 weeks after the secondary boost, whereas IgA or SIgA responses in bronchoalveolar lavage (BAL) were not significantly increased after immunization with RA. Analyses of different isotype responses to vaccination and different sampling sites, revealed significant correlations between IgG and IgA responses in serum, and between IgG in serum and jejunum, while IgA in jejunum was neither correlated with IgA in serum nor with IgG in jejunum. This is indicative of IgG in jejunum being primarily a transudate from serum, while IgA is not. Jejunum SIgA correlated significantly with jejunum IgA and with both serum SIgA and IgA. Our results thus support the use of SC-specific reagents for mucosal SIgA responses, although IgA reagents to a lesser extent also reflects local antibodies. Although the IgA and SIgA levels in BAL were not significantly different with or without RA, we observed a significant correlation of vaccine-specific SIgA in jejunum and BAL, indicating a level of commonality in the regulation of mucosal antibodies in gut and respiratory system. In conclusion, an adjuvant with high concentration of RA was shown to increase the local intestinal mucosal antibody response after parenteral immunization in pigs.

Mucosal immune response in biology, disease prevention and treatment

The mucosal immune system, as the most extensive peripheral immune network, serves as the frontline defense against a myriad of microbial and dietary antigens. It is crucial in preventing pathogen invasion and establishing immune tolerance. A comprehensive understanding of mucosal immunity is essential for developing treatments that can effectively target diseases at their entry points, thereby minimizing the overall impact on the body. Despite its importance, our knowledge of mucosal immunity remains incomplete, necessitating further research. The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has underscored the critical role of mucosal immunity in disease prevention and treatment. This systematic review focuses on the dynamic interactions between mucosa-associated lymphoid structures and related diseases. We delve into the basic structures and functions of these lymphoid tissues during disease processes and explore the intricate regulatory networks and mechanisms involved. Additionally, we summarize novel therapies and clinical research advances in the prevention of mucosal immunity-related diseases. The review also addresses the challenges in developing mucosal vaccines, which aim to induce specific immune responses while maintaining tolerance to non-pathogenic microbes. Innovative therapies, such as nanoparticle vaccines and inhalable antibodies, show promise in enhancing mucosal immunity and offer potential for improved disease prevention and treatment.

Lung mucosal immunity to NTHi vaccine antigens: Antibodies in sputum of chronic obstructive pulmonary disease patients

Chronic obstructive pulmonary disease (COPD) is a common chronic respiratory illness in older adults. A major cause of COPD-related morbidity and mortality is acute exacerbation of COPD (AECOPD). Bacteria in the lungs play a role in exacerbation development, and the most common pathogen is non-typeable Haemophilus influenzae (NTHi). A vaccine to prevent AECOPD containing NTHi surface antigens was tested in a clinical trial. This study measured IgG and IgA against NTHi vaccine antigens in sputum. Sputum samples from 40 COPD patients vaccinated with the NTHi vaccine were collected at baseline and 30 days after the second dose. IgG and IgA antibodies against the target antigens and albumin were analyzed in the sputum. We compared antibody signals before and after vaccination, analyzed correlation with disease severity and between sputum and serum samples, and assessed transudation. Antigen-specific IgG were absent before vaccination and present with high titers after vaccination. Antigen-specific IgA before and after vaccination were low but significantly different for two antigens. IgG correlated between sputum and serum, and between sputum and disease severity. Sputum albumin was higher in patients with severe COPD than in those with moderate COPD, suggesting changes in transudation played a role. We demonstrated that immunization with the NTHi vaccine induces antigen-specific antibodies in sputum. The correlation between IgG from sputum and serum and the presence of albumin in the sputum of severe COPD patients suggested transudation of antibodies from the serum to the lungs, although local IgG production could not be excluded.Clinical Trial Registration: NCT02075541.

Unmasking the potential of secretory IgA and its pivotal role in protection from respiratory viruses

Mucosal immunity has regained its spotlight amidst the ongoing Coronavirus disease 19 (COVID-19) pandemic, with numerous studies highlighting the crucial role of mucosal secretory IgA (SIgA) in protection against Severe acute respiratory syndrome coronavirus-2 or SARS-CoV-2 infections. The observed limitations in the efficacy of currently authorized COVID-19 vaccines in inducing effective mucosal immune responses remind us of the limitations of systemic vaccination in promoting protective mucosal immunity. This resurgence of interest has motivated the development of vaccine platforms capable of enhancing mucosal responses, specifically the SIgA response, and the development of IgA-based therapeutics. Recognizing viral respiratory infections as a global threat, we would like to comprehensively review the existing knowledge on mucosal immunity, with a particular emphasis on SIgA, in the context of SARS-CoV-2, influenza, and Respiratory Syncytial Virus (RSV) infections. This review aims to describe the structural and functional specificities of SIgA, along with its nuanced role in combating influenza, RSV, and SARS-CoV-2 infections. Subsequent sections further elaborate promising vaccine strategies, including mucosal vaccines against Influenza, RSV, and SARS-CoV-2 respiratory viruses, currently undergoing preclinical and clinical development. Additionally, we address the challenges associated with mucosal vaccine development, concluding with a discussion on IgA-based therapeutics as a promising platform for the treatment of viral respiratory infections. This comprehensive review not only synthesizes current insights into mucosal immunity but also identifies critical knowledge gaps, strengthening the way for further advancements in our current understanding and approaches to combat respiratory viral threats.

Olfactory immune response to SARS-CoV-2

Numerous pathogens can infect the olfactory tract, yet the pandemic caused by SARS-CoV-2 has strongly emphasized the importance of the olfactory mucosa as an immune barrier. Situated in the nasal passages, the olfactory mucosa is directly exposed to the environment to sense airborne odorants; however, this also means it can serve as a direct route of entry from the outside world into the brain. As a result, olfactotropic infections can have serious consequences, including dysfunction of the olfactory system, CNS invasion, dissemination to the lower respiratory tract, and transmission between individuals. Recent research has shown that a distinctive immune response is needed to protect this neuronal and mucosal tissue. A better understanding of innate, adaptive, and structural immune barriers in the olfactory mucosa is needed to develop effective therapeutics and vaccines against olfactotropic microbes such as SARS-CoV-2. Here, we summarize the ramifications of SARS-CoV-2 infection of the olfactory mucosa, review the subsequent immune response, and discuss important areas of future research for olfactory immunity to infectious disease.

Mucosal immunity in health care workers' respiratory tracts in the post-COVID-19 period

Coronavirus disease (COVID-19) has generated interest in the assessment of systemic immune status, but existing knowledge about mucosal immunity is clearly insufficient to understand the full pathogenetic mechanisms of the disease. The aim of this study was to evaluate the long-term effects of novel coronavirus infection on mucosal immunity in the postinfection period among health care workers (HCWs). A total of 180 health care workers with and without a history of COVID-19 who ranged in age from 18 to 65 years were enrolled in this one-stage, cross-sectional study. The study subjects completed the 36-Item Short Form (36) Health Survey (SF-36) and the Fatigue Assessment Scale. Secretory immunoglobulin A (sIgA) and total immunoglobulin G (IgG) levels were quantified in saliva samples, induced sputum samples, and nasopharyngeal and oropharyngeal scrapings by an enzyme-linked immunosorbent assay. Specific anti-SARS-CoV-2 IgG antibodies were quantified in serum samples by chemiluminescence immunoassay. Analysis of the questionnaire data showed that all HCWs with a history of COVID-19 reported health problems that limited their daily activities and negative changes in their emotional health three months after the disease, regardless of its severity. The following shifts were detected in the adaptive arm of the immune response in different mucosal compartments. Among subjects who had severe or moderate-to-severe COVID-19, salivary sIgA levels were significantly higher than those in the control group (p < 0.05 and p < 0.005, respectively). Compared to the subjects in the control group, all subjects with prior COVID-19 had significantly higher levels of total IgG in induced sputum. In the group of patients who had had severe infection, total IgG in saliva was also higher (p < 0.05). A direct statistically significant correlation was also detected between the levels of total IgG in all studied samples and the levels of specific IgG antibodies against SARS-CoV-2 in the serum. A significant correlation was observed between total IgG levels and the parameters of physical and social activities, mental health, and fatigue levels. Our study demonstrated long-term changes in the humoral mucosal immune response, which were most pronounced in health care workers with a history of severe or moderate-to-severe COVID-19, and an association of these changes with certain clinical signs of post-COVID-19 syndrome.

Mucosal vaccines for SARS-CoV-2: triumph of hope over experience

Currently approved COVID-19 vaccines administered parenterally induce robust systemic humoral and cellular responses. While highly effective against severe disease, there is reduced effectiveness of these vaccines in preventing breakthrough infection and/or onward transmission, likely due to poor immunity elicited at the respiratory mucosa. As such, there has been considerable interest in developing novel mucosal vaccines that engenders more localised immune responses to provide better protection and recall responses at the site of virus entry, in contrast to traditional vaccine approaches that focus on systemic immunity. In this review, we explore the adaptive components of mucosal immunity, evaluate epidemiological studies to dissect if mucosal immunity conferred by parenteral vaccination or respiratory infection drives differential efficacy against virus acquisition or transmission, discuss mucosal vaccines undergoing clinical trials and assess key challenges and prospects for mucosal vaccine development.

Live-attenuated vaccine sCPD9 elicits superior mucosal and systemic immunity to SARS-CoV-2 variants in hamsters

Vaccines play a critical role in combating the COVID-19 pandemic. Future control of the pandemic requires improved vaccines with high efficacy against newly emerging SARS-CoV-2 variants and the ability to reduce virus transmission. Here we compare immune responses and preclinical efficacy of the mRNA vaccine BNT162b2, the adenovirus-vectored spike vaccine Ad2-spike and the live-attenuated virus vaccine candidate sCPD9 in Syrian hamsters, using both homogeneous and heterologous vaccination regimens. Comparative vaccine efficacy was assessed by employing readouts from virus titrations to single-cell RNA sequencing. Our results show that sCPD9 vaccination elicited the most robust immunity, including rapid viral clearance, reduced tissue damage, fast differentiation of pre-plasmablasts, strong systemic and mucosal humoral responses, and rapid recall of memory T cells from lung tissue after challenge with heterologous SARS-CoV-2. Overall, our results demonstrate that live-attenuated vaccines offer advantages over currently available COVID-19 vaccines.

Intracellular immunoglobulin A (icIgA) in protective immunity and vaccines

Virus neutralization at respiratory mucosal surfaces is important in the prevention of infection. Mucosal immunity is mediated mainly by extracellular secretory immunoglobulin A (sIgA) and its role has been well studied. However, the protective role of intracellular specific IgA (icIgA) is less well defined. Initially, in vitro studies using epithelial cell lines with surface expressed polymeric immunoglobulin receptor (pIgR) in transwell culture chambers have shown that icIgA can neutralize influenza, parainfluenza, HIV, rotavirus and measles viruses. This effect appears to involve an interaction between polymeric immunoglobulin A (pIgA) and viral particles within an intracellular compartment, since IgA is transported across the polarized cell. Co-localization of specific icIgA with influenza virus in patients' (virus culture positive) respiratory epithelial cells using well-characterized antisera was initially reported in 2018. This review provides a summary of in vitro studies with icIgA on colocalization and neutralization of the above five viruses. Two other highly significant respiratory infectious agents with severe global impacts viz. SARS-2 virus (CoViD pandemic) and the intracellular bacterium-Mycobacterium tuberculosis-are discussed. Further studies will provide more detailed understanding of the mechanisms and kinetics of icIgA neutralization in relation to viral entry and early replication steps with a specific focus on mucosal infections. This will inform the design of more effective vaccines against infectious agents transmitted via the mucosal route.

Pilot genome-wide association study of antibody response to inactivated SARS-CoV-2 vaccines

Vaccines are a key weapon against the COVID-19 pandemic caused by SARS-CoV-2. However, there are inter-individual differences in immune response to SARS-CoV-2 vaccines and genetic contributions to these differences have barely been investigated. Here, we performed genome-wide association study (GWAS) of antibody levels in 168 inactivated SARS-CoV-2 vaccine recipients. A total of 177 SNPs, corresponding to 41 independent loci, were identified to be associated with IgG, total antibodies or neutral antibodies. Specifically, the rs4543780, the intronic variant of FAM89A gene, was associated with total antibodies level and was annotated as a potential regulatory variant affecting gene expression of FAM89A, a biomarker differentiating bacterial from viral infections in febrile children. These findings might advance our knowledge of the molecular mechanisms driving immunity to SARS-CoV-2 vaccine.