RESUMO
Maternal immune responses during pregnancy protect the growing fetus by clearing infection, preventing its vertical transmission, and through transplacental transfer of protective immune mediators to the fetus. How maternal immune response balances SARS-CoV-2 antiviral responses with transplacental transfer of protection to the fetus remains unclear. Our study shows that upon SARS-CoV-2 maternal infection, neutralizing antibodies (NAbs) are infrequently detected in cord blood. We uncovered that this is due to impaired IgG-NAbs placental transfer in symptomatic infection and to the predominance of maternal SARS-CoV-2 NAbs of the IgA and IgM isotypes, which are prevented from crossing the placenta. Crucially, the decision between favoring maternal antiviral response or transplacental transfer of immune protection to the fetus appears to hinge on the balance between IL-6 and IL-10 induced by SARS-CoV-2 infection, decreasing or increasing transplacental transfer of IgG-NAbs, respectively. In addition, IL-10 inversely correlates with maternal NK cell frequency. Finally, we found that ongoing infection favored perinatal transfer of maternal NK cells, highlighting a maternal sponsored mechanism to protect the newborn from horizontal transmission of infection. Our data point to an evolutionary trade-off which at once optimizes maternal viral clearance and vertical transfer of immune protection during the more susceptible perinatal period. Brief SummaryIn SARS-CoV-2 maternal infection, the balance between maternal antiviral response and transplacental transfer of cellular and humoral (NAb) protection hinges on maternal IL-6 and IL-10.
RESUMO
Structured abstractO_ST_ABSIMPORTANCEC_ST_ABSAdults are being vaccinated against SARS-CoV-2 worldwide, but the longitudinal protection of these vaccines is uncertain, given the ongoing appearance of SARS-CoV-2 variants. Children are susceptible to infection, and some studies reported that they actively transmit the virus even when asymptomatic, thus affecting the community. Methods to easily test infected children and track the virus they carry are in demand. OBJECTIVETo determine if saliva is an effective sample for detecting SARS-CoV-2 RNA and antibodies in children aged 10 years and under, and associate viral RNA levels to infectivity. DESIGN, SETTING, AND PARTICIPANTSIn this cross-sectional study, saliva SARS-CoV-2 RT-qPCR tests, with and without RNA extraction, were validated in 49 hospitalized adults. The test was then applied to 85 children, aged 10 years and under, admitted to the hospital regardless of COVID-19 symptomatology. Amongst 85 children, 29 (63.0%) presented at least one COVID-19 symptom, 46 (54.1%) were positive for SARS-CoV-2 infection, 28 (32.9%) were under the age of 1 and the mean (SD) age was 3.8 (3.4) years. Saliva samples were collected up to 48 h after a positive test by nasopharyngeal (NP) swab-RT-qPCR. EXPOSUREInfection by SARS-COV-2 in adults up to 8 days post-symptom onset. Children admitted to hospital for any reason and therefore with unclear onset of SARS-CoV-2 infection. MAIN OUTCOMES AND MEASURESSaliva RT-qPCR up to CT<37 accurately identifies SARS-CoV-2 infected children, with viral infectivity in tissue culture restricted to CT<26. RESULTSIn adults, the accuracy of the saliva SARS-CoV-2 RT-qPCR test was 98.0% (95% confidence intervals [CI]: 89.3%-100%) as compared to NP-RT-qPCR. In children, the sensitivity, specificity, and accuracy of saliva-RT-qPCR tests compared to NP swab-RT-qPCR were, respectively, 84.8% (71.8%-92.4%), 100% (91.0%-100%), and 91.8% (84.0%- 96.6%) with RNA extraction and 81.8% (68.0%-90.5%), 100% (91.0%-100%), and 90.4% (82.1%-95.0%) without RNA extraction. The threshold for rescuing infectious particles from saliva was CT<26. There were significant IgM positive responses to the spike protein and its receptor-binding domain (RBD) among children positive for SARS-CoV-2 by NP swab and negative by saliva compared to other groups, indicating late infection onset (>7-10 days). CONCLUSIONS AND RELEVANCESaliva-molecular testing is suitable in children aged 10 years and under, including infants aged <1 year, even bypassing RNA extraction methods. Importantly, the detected viral RNA levels were significantly above the infectivity threshold in several samples. Further investigation is required to understand how SARS-CoV-2 RNA levels correlate with viral transmission. Key PointsO_ST_ABSQuestionC_ST_ABSIs saliva reverse transcription-quantitative polymerase chain reaction (RT-qPCR) testing (with and without RNA extraction) suitable to identify SARS-CoV-2 infected young children and can the cycle threshold (CT) be associated with infectivity in a heterogeneous population admitted to hospital for COVID-19-related and unrelated reasonsa FindingsIn this cross-sectional study of 85 children aged 10 years and under, RT-qPCR in saliva samples subjected or not to RNA extraction accurately detected SARS-CoV-2 RNA and infectious viruses could be recovered from CTs below 26. MeaningSaliva sampling coupled to RT-qPCR and specific antibody detection efficiently identifies infants and children infected with SARS-CoV-2. This approach is suitable for surveillance in kindergarten and school settings.
RESUMO
Understanding SARS-CoV-2 evolution and host immunity is critical to control COVID-19 pandemics. At the core is an arms-race between SARS-CoV-2 antibody and angiotensin-converting enzyme 2 (ACE2) recognition, a function of the viral protein spike. Mutations in spike impacting antibody and/or ACE2 binding are appearing worldwide, with the effect of mutation synergy still incompletely understood. We engineered 25 spike-pseudotyped lentiviruses containing individual and combined mutations, and confirmed that E484K evades antibody neutralization elicited by infection or vaccination, a capacity augmented when complemented by K417N and N501Y mutations. In silico analysis provided an explanation for E484K immune evasion. E484 frequently engages in interactions with antibodies but not with ACE2. Importantly, we identified a novel amino acid of concern, S494, which shares a similar pattern. Using the already circulating mutation S494P, we found that it reduces antibody neutralization of convalescent and post-immunization sera, particularly when combined with E484K and N501Y. Our analysis of synergic mutations provides a landscape for hotspots for immune evasion and for targets for therapies, vaccines and diagnostics. One-Sentence SummaryAmino acids in SARS-CoV-2 spike protein implicated in immune evasion are biased for binding to neutralizing antibodies but dispensable for binding the host receptor angiotensin-converting enzyme
