Persistent symptoms after COVID-19 in children and adolescents from Argentina.

OBJECTIVES: Although long COVID-19 is widely recognized in adults, less information is available about this condition in children, especially in developing countries. Here, we studied the long-term symptoms of SARS-CoV-2 infection beyond 3 months and the associated risk factors in a pediatric population. METHODS: This observational study included 639 Argentinian children and adolescents with previously confirmed COVID-19 from June 2020-June 2021 and 577 children without previous COVID-19. Parents completed a survey about symptoms that their child had for >3 months after the diagnosis of SARS-CoV-2 infection. RESULTS: At least one persistent symptom was observed more frequently in children with previous COVID-19 than in the non-COVID-19 group (34% vs 13%, P <0.0001). SARS-CoV-2 infection increased the risk of headache, dizziness, loss of taste, dyspnea, cough, fatigue, muscle pain, and loss of weight by three- to seven-fold. The loss of smell was only reported in infected children. After controlling for the other variables, older age, symptomatic COVID-19, and comorbidities were independent predictors of long-term symptoms. CONCLUSIONS: One-third of children experienced persistent symptoms after COVID-19. Older age, symptomatic infection, and comorbidities were shown to be risk factors for long COVID-19. Pediatric long COVID-19 is a new condition that requires further investigation.

Antibody response against SARS-CoV-2 variants of concern in children infected with pre-Omicron variants: An observational cohort study.

BACKGROUND: Despite that pediatric COVID-19 is usually asymptomatic or mild, SARS-CoV-2 infection typically results in the development of an antibody response. Contradictory observations have been reported when the antibody response of children and adults were compared in terms of strength, specificity and perdurability. METHODS: This observational study includes three cohorts infected with SARS-CoV-2 between March 2020-July 2021: unvaccinated infected children (n=115), unvaccinated infected adults (n=62), and vaccinated infected children (n=76). Plasma anti-spike IgG antibodies and neutralising activity against Wuhan, Delta and Omicron variants after 7-17 months post-infection were analysed. FINDINGS: More than 95% of unvaccinated infected children and adults remained seropositive when evaluated at 382-491 and 386-420 days after infection, respectively. Anti-spike IgG titers and plasma neutralising activity against Wuhan, Delta and Omicron variants were higher in children compared to adults. No differences were found when unvaccinated infected children were stratified by age, gender or presence/absence of symptoms in the acute phase of SARS-CoV-2 infection, but a slight decrease in the antibody response was observed in those with comorbidities. Vaccination of previously infected children with two doses of the inactivated BBIBP-CorV or the mRNA vaccines, BNT162b2 and/or mRNA-1273, further increased anti-spike IgG titers and neutralising activity against Wuhan, Delta and Omicron variants. INTERPRETATION: Unvaccinated infected children mount a more potent and sustained antibody response compared with adults, which is significantly increased after vaccination. Further studies including not only the analysis of the immune response but also the effectiveness to prevent reinfections by the different Omicron lineages are required to optimise vaccination strategy in children. FUNDING: National Agency for Scientific and Technological Promotion from Argentina (PICTO-COVID-SECUELAS-00007 and PMO-BID-PICT2018-2548).

Extracellular ATP and Imbalance of CD4+ T Cell Compartment in Pediatric COVID-19.

Severe COVID-19 in children is rare, but the reasons underlying are unclear. Profound alterations in T cell responses have been well characterized in the course of adult severe COVID-19, but little is known about the T cell function in children with COVID-19. Here, we made three major observations in a cohort of symptomatic children with acute COVID-19: 1) a reduced frequency of circulating FoxP3+ regulatory T cells, 2) the prevalence of a TH17 polarizing microenvironment characterized by high plasma levels of IL-6, IL-23, and IL17A, and an increased frequency of CD4+ T cells expressing ROR-γt, the master regulator of TH17 development, and 3) high plasma levels of ATP together with an increased expression of the P2X7 receptor. Moreover, that plasma levels of ATP displayed an inverse correlation with the frequency of regulatory T cells but a positive correlation with the frequency of CD4+ T cells positive for the expression of ROR-γt. Collectively, our data indicate an imbalance in CD4+ T cell profiles during pediatric COVID-19 that might favor the course of inflammatory processes. This finding also suggests a possible role for the extracellular ATP in the acquisition of an inflammatory signature by the T cell compartment offering a novel understanding of the involved mechanisms.

Efecto del empleo de prescripciones informatizadas en la seguridad de pacientes pediátricos hospitalizados / Effect of electronic prescriptions on the safety of hospitalized pediatric patients

Introducción. Los errores en prescripción médica (EPM) son la causa más frecuente de errores prevenibles. El empleo de sistemas de prescripción informatizada (PI) contribuiría a disminuir el error y a mejorar la calidad de atención. Objetivos. Evaluar el efecto de la PI en la prevalencia de EPM y eventos adversos (EA) relacionados en pacientes pediátricos hospitalizados. Evaluar la adherencia, aceptabilidad y apropiabilidad de la herramienta por parte de los usuarios. Método. Diseño híbrido, descriptivo y cuasiexperimental tipo antes-después. Se incluyeron prescripciones médicas de pacientes hospitalizados, calculando la prevalencia de EPM y EA relacionados, en los períodos pre-y pos implementación de la PI en un hospital pediátrico (HP) y en uno general (HG) que se tomó como control. Se evaluó la adherencia mediante la proporción de las PI sobre las totales registradas en el período posimplementación. Se evaluó la aceptabilidad y apropiabilidad de la implementación por encuesta a los usuarios. Resultados. Al comparar la prevalencia de EPM pre- y posimplementación en el HP, se observó una disminución estadísticamente significativa en los dos hospitales: HP 29,1 versus 19,9 EPM/100 prescripciones (OR: 1,65; IC95 %: 1,34-2,02; p < 0,01). En el HG 24,9 versus 13,6 EPM/100 prescripciones (OR: 2,1; IC95 %: 1,5-2,8; p < 0,01). La tasa de adherencia global a la PI fue del 83 %. La implementación presentó aceptabilidad y apropiabilidad satisfactoria. Conclusión. La prevalencia de EPM se redujo un 30 % posimplementación. La adherencia global a la herramienta fue satisfactoria

Introduction. Prescription errors are the most common cause of preventable errors. Electronic prescription (EP) systems may help to reduce errors and improve the quality of care. Objectives. To assess the effect of EP on the prevalence of prescription errors and related adverse events (AE) among hospitalized pediatric patients. To assess EP adherence, acceptability, and suitability among users. Method. Hybrid, descriptive, and quasi-experimental, before-and-after design. Prescriptions made to hospitalized patients were included, estimating the prevalence of prescription errors and related AE in the pre- and post- EP implementation periods at a children's hospital (CH) and a general hospital (GH) used as control. Adherence was assessed based on the proportion of EP among all prescriptions registered in the post-implementation period. The acceptability and suitability of EP implementation was assessed via a user survey. Results. The prevalence of prescription errors pre- and post-EP implementation at the CH was compared and a statistically significant reduction was observed in both hospitals: CH: 29.1 versus 19.9 prescription errors/100 prescriptions (OR: 1.65; 95% CI: 1.34-2.02;p < 0.01). GH: 24.9 versus 13.6 prescription errors/100 prescriptions (OR: 2.1; 95% CI: 1.5-2.8; p < 0.01). The rate of overall adherence to EP was 83%. The implementation of EP was adequately acceptable and suitable. Conclusion. The prevalence of prescription errors reduced 30% after the implementation of EP. The overall adherence to EP was adequate.

Effect of electronic prescriptions on the safety of hospitalized pediatric patients. / Efecto del empleo de prescripciones informatizadas en la seguridad de pacientes pediátricos hospitalizados.

INTRODUCTION: Prescription errors are the most common cause of preventable errors. Electronic prescription (EP) systems may help to reduce errors and improve the quality of care. OBJECTIVES: To assess the effect of EP on the prevalence of prescription errors and related adverse events (AE) among hospitalized pediatric patients. To assess EP adherence, acceptability, and suitability among users. METHODS: Hybrid, descriptive, and quasi-experimental, before-and-after design. Prescriptions made to hospitalized patients were included, estimating the prevalence of prescription errors and related AE in the pre- and post- EP implementation periods at a children's hospital (CH) and a general hospital (GH) used as control. Adherence was assessed based on the proportion of EP among all prescriptions registered in the post-implementation period. The acceptability and suitability of EP implementation was assessed via a user survey. RESULTS: The prevalence of prescription errors pre- and post-EP implementation at the CH was compared and a statistically significant reduction was observed in both hospitals: CH: 29.1 versus 19.9 prescription errors/100 prescriptions (OR: 1.65; 95% CI: 1.34-2.02; p < 0.01). GH: 24.9 versus 13.6 prescription errors/100 prescriptions (OR: 2.1; 95% CI: 1.5-2.8; p < 0.01). The rate of overall adherence to EP was 83%. The implementation of EP was adequately acceptable and suitable. CONCLUSION: The prevalence of prescription errors reduced 30% after the implementation of EP. The overall adherence to EP was adequate.

Introducción. Los errores en prescripción médica (EPM) son la causa más frecuente de errores prevenibles. El empleo de sistemas de prescripción informatizada (PI) contribuiría a disminuir el error y a mejorar la calidad de atención. Objetivos. Evaluar el efecto de la PI en la prevalencia de EPM y eventos adversos (EA) relacionados en pacientes pediátricos hospitalizados. Evaluar la adherencia, aceptabilidad y apropiabilidad de la herramienta por parte de los usuarios. Método. Diseño híbrido, descriptivo y cuasiexperimental tipo antes-después. Se incluyeron prescripciones médicas de pacientes hospitalizados, calculando la prevalencia de EPM y EA relacionados, en los períodos pre-y posimplementación de la PI en un hospital pediátrico (HP) y en uno general (HG) que se tomó como control. Se evaluó la adherencia mediante la proporción de las PI sobre las totales registradas en el período posimplementación. Se evaluó la aceptabilidad y apropiabilidad de la implementación por encuesta a los usuarios. Resultados. Al comparar la prevalencia de EPM pre- y posimplementación en el HP, se observó una disminución estadísticamente significativa en los dos hospitales: HP 29,1 versus 19,9 EPM/100 prescripciones (OR: 1,65; IC95 %: 1,34-2,02; p < 0,01). En el HG 24,9 versus 13,6 EPM/100 prescripciones (OR: 2,1; IC95 %: 1,5-2,8; p < 0,01). La tasa de adherencia global a la PI fue del 83 %. La implementación presentó aceptabilidad y apropiabilidad satisfactoria. Conclusión. La prevalencia de EPM se redujo un 30 % posimplementación. La adherencia global a la herramienta fue satisfactoria.

A poor and delayed anti-SARS-CoV2 IgG response is associated to severe COVID-19 in children.

BACKGROUND: Most children and youth develop mild or asymptomatic disease during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, a very small number of patients suffer severe Coronavirus induced disease 2019 (COVID-19). The reasons underlying these different outcomes remain unknown. METHODS: We analyzed three different cohorts: children with acute infection (n=550), convalescent children (n=138), and MIS-C (multisystem inflammatory syndrome in children, n=42). IgG and IgM antibodies to the spike protein of SARS-CoV-2, serum-neutralizing activity, plasma cytokine levels, and the frequency of circulating Follicular T helper cells (cTfh) and plasmablasts were analyzed by conventional methods. FINDINGS: Fifty-eight percent of the children in the acute phase of infection had no detectable antibodies at the time of sampling while a seronegative status was found in 25% and 12% of convalescent and MIS-C children, respectively. When children in the acute phase of the infection were stratified according disease severity, we found that contrasting with the response of children with asymptomatic, mild and moderate disease, children with severe COVID-19 did not develop any detectable response. A defective antibody response was also observed in the convalescent cohort for children with severe disease at the time of admission. This poor antibody response was associated to both, a low frequency of cTfh and a high plasma concentration of inflammatory cytokines. INTERPRETATION: A weak and delayed kinetic of antibody response to SARS-CoV-2 together with a systemic pro-inflammatory profile characterize pediatric severe COVID-19. Because comorbidities are highly prevalent in children with severe COVID-19, further studies are needed to clarify their contribution in the weak antibody response observed in severe disease. FUNDING: National Agency for Scientific and Technological Promotion from Argentina (IP-COVID-19-0277 and PMO-BID-PICT2018-2548).

Children hospitalized for COVID-19 during the first winter of the pandemic in Buenos Aires, Argentina.

BACKGROUND: Although there are reports on COVID-19 in pediatrics, the characteristics of the population of each country, its health systems, and how the pandemic was addressed could give the disease distinctive features worldwide. We aimed to describe the characteristics of patients hospitalized for COVID-19 in a tertiary pediatric hospital in the City of Buenos Aires, Argentina. METHODS: We conducted a descriptive study, including all patients hospitalized for COVID-19 from 04/26/2020 to 10/31/2020 in a tertiary pediatric hospital. We described the demographic, clinical, and epidemiological characteristics of the patients. RESULTS: During the period studied, 578 patients were hospitalized with COVID-19. The median age was 4.2 years, and 83% reported close contact with a confirmed COVID-19 case. Regarding severity, 30.8% were asymptomatic, and 60.4% showed mild, 7.4% moderate, and 1.4% severe symptoms. Among symptomatic patients, fever was the most frequent symptom, followed by sore throat and cough. CONCLUSIONS: We reported 578 cases of children and adolescents hospitalized with COVID-19, of which the majority showed mild or asymptomatic disease.

Blood neutrophils from children with COVID-19 exhibit both inflammatory and anti-inflammatory markers.

BACKGROUND: Perhaps reflecting that children with COVID-19 rarely exhibit severe respiratory symptoms and often remain asymptomatic, little attention has been paid to explore the immune response in pediatric COVID-19. Here, we analyzed the phenotype and function of circulating neutrophils from children with COVID-19. METHODS: An observational study including 182 children with COVID-19, 21 children with multisystem inflammatory syndrome (MIS-C), and 40 healthy children was performed in Buenos Aires, Argentina. Neutrophil phenotype was analyzed by flow cytometry in blood samples. Cytokine production, plasma levels of IgG antibodies directed to the spike protein of SARS-CoV-2 and citrullinated histone H3 were measured by ELISA. Cell-free DNA was quantified by fluorometry. FINDINGS: Compared with healthy controls, neutrophils from children with COVID-19 showed a lower expression of CD11b, CD66b, and L-selectin but a higher expression of the activation markers HLA-DR, CD64 and PECAM-1 and the inhibitory receptors LAIR-1 and PD-L1. No differences in the production of cytokines and NETs were observed. Interestingly, the expression of CD64 in neutrophils and the serum concentration of IgG antibodies directed to the spike protein of SARS-CoV-2 distinguished asymptomatic from mild and moderate COVID-19. INTERPRETATION: Acute lung injury is a prominent feature of severe COVID-19 in adults. A low expression of adhesion molecules together with a high expression of inhibitory receptors in neutrophils from children with COVID-19 might prevent tissue infiltration by neutrophils preserving lung function. FUNDING: This study was supported by the Ministry of Science and Technology (National Agency for Scientific and Technological Promotion, IP-COVID-19-0277 and PMO BID PICT 2018-2548), and University of Buenos Aires from Argentina (20020170100573BA).

Pacientes asistidos en el Departamento de Medicina de un hospital pediátrico en el inicio de la pandemia COVID-19 en Buenos Aires, Argentina / Patients assisted at the Department of Medicine of a pediatric hospital at the beginning of the COVID-19 pandemic in Buenos Aires, Argentina

Introducción. A pesar de la magnitud de la pandemia por COVID-19, la información sobre su desarrollo en pediatría es aún limitada. Se describen las características de pacientes hospitalizados por COVID-19 en un hospital pediátrico durante los primeros tres meses de la pandemia.Método. Estudio descriptivo, que incluyó a todos los pacientes hospitalizados por COVID-19, desde el 1/4/2020 al 30/6/2020.Resultados. Se hospitalizaron 191 pacientes por COVID-19; la edad mediana fue 7,7 años; el 89 % presentaban antecedente de contacto. El 35,6 % se consideraron asintomáticos; el 61,2 %, leves, y el 3,2 %, moderados (no se observaron pacientes graves). Ninguno recibió tratamiento específico para la enfermedad. Los síntomas más frecuentes fueron fiebre, odinofagia y tos. La duración de la hospitalización tuvo una mediana de 6 días.Conclusión. Se reportaron 191 casos de niños y adolescentes hospitalizados por COVID-19. La mayoría fueron asintomáticos o presentaron enfermedad leve.

Introduction. Despite the magnitude of the COVID-19 pandemic, the information about its development in pediatrics is still limited. This report describes the characteristics of patients admitted to a children's hospital due to COVID-19 during the first three months of the pandemic.Method. Descriptive study including all patients hospitalized due to COVID-19 between 4/1/2020 and 6/30/2020.Results. A total of 191 patients were hospitalized due to COVID-19; their median age was 7.7 years; 89 % had a history of close contact. Of them, 35.6 % were considered asymptomatic; 61.2 %, mild cases; and 3.2 %, moderate cases (no severe cases). None of them received a specific treatment for the disease. The most common symptoms were fever, sore throat, and cough. The median length of stay was 6 days.Conclusion. A total of 191 cases of children and adolescents admitted due to COVID-19 are reported. Most were asymptomatic or presented with a mild disease

Patients assisted at the Department of Medicine of a pediatric hospital at the beginning of the COVID-19 pandemic in Buenos Aires, Argentina. / Pacientes asistidos en el Departamento de Medicina de un hospital pediátrico en el inicio de la pandemia COVID-19 en Buenos Aires, Argentina.

INTRODUCTION: Despite the magnitude of the COVID-19 pandemic, the information about its development in pediatrics is still limited. This report describes the characteristics of patients admitted to a children's hospital due to COVID-19 during the first three months of the pandemic. METHOD: Descriptive study including all patients hospitalized due to COVID-19 between 4/1/2020 and 6/30/2020. RESULTS: A total of 191 patients were hospitalized due to COVID-19; their median age was 7.7 years; 89% had a history of close contact. Of them, 35.6 % were considered asymptomatic; 61.2 %, mild cases; and 3.2 %, moderate cases (no severe cases). None of them received a specific treatment for the disease. The most common symptoms were fever, sore throat, and cough. The median length of stay was 6 days. CONCLUSION: A total of 191 cases of children and adolescents admitted due to COVID-19 are reported. Most were asymptomatic or presented with a mild disease.

Introducción. A pesar de la magnitud de la pandemia por COVID-19, la información sobre su desarrollo en pediatría es aún limitada. Se describen las características de pacientes hospitalizados por COVID-19 en un hospital pediátrico durante los primeros tres meses de la pandemia. Método. Estudio descriptivo, que incluyó a todos los pacientes hospitalizados por COVID-19, desde el 1/4/2020 al 30/6/2020. Resultados. Se hospitalizaron 191 pacientes por COVID-19; la edad mediana fue 7,7 años; el 89 % presentaban antecedente de contacto. El 35,6 % se consideraron asintomáticos; el 61,2 %, leves, y el 3,2 %, moderados (no se observaron pacientes graves). Ninguno recibió tratamiento específico para la enfermedad. Los síntomas más frecuentes fueron fiebre, odinofagia y tos. La duración de la hospitalización tuvo una mediana de 6 días. Conclusión. Se reportaron 191 casos de niños y adolescentes hospitalizados por COVID-19. La mayoría fueron asintomáticos o presentaron enfermedad leve.

Fcγ Receptor IIa (FCGR2A) Polymorphism Is Associated With Severe Respiratory Syncytial Virus Disease in Argentinian Infants.

Background: Most patients with respiratory syncytial virus (RSV) infection requiring hospitalization have no risk factors for severe disease. Genetic variation in the receptor for the Fc portion of IgG (FcγR) determines their affinity for IgG subclasses driving innate and adaptive antiviral immunity. We investigated the relationship between FcγRIIa-H131R polymorphism and RSV disease. Methods: Blood samples were collected from 182 infants ≤24-month-old (50 uninfected, 114 RSV-infected with moderate course and 18 suffering severe disease). FcγRIIa-H131R SNP genotypic frequencies (HH, HR, RR) and anti-RSV IgG1, IgG2 and IgG3 levels were studied. Results: Genotypic frequencies for FcγRIIa-H131R SNP were comparable between uninfected and RSV-infected infants. In contrast, we found a significant higher frequency of HH genotype in severe RSV-infected children compared to moderate patients. Among severe group, HH infants presented more factors associated to severity than HR or RR patients did. Furthermore, compared to moderate RSV-infected infants, severe patients showed higher levels of anti-RSV IgG1 and IgG3. Conclusions: We found an association between an FcγRIIa (H131) polymorphism and severe RSV disease, which points towards a critical role for interactions between FcγRs and immune complexes in RSV pathogenesis. This genetic factor could also predict the worse outcome and identify those infants at risk during hospitalization.

CD32 Ligation Promotes the Activation of CD4+ T Cells.

Low affinity receptors for the Fc portion of IgG (FcγRs) represent a critical link between innate and adaptive immunity. Immune complexes (ICs) are the natural ligands for low affinity FcγRs, and high levels of ICs are usually detected in both, chronic viral infections and autoimmune diseases. The expression and function of FcγRs in myeloid cells, NK cells and B cells have been well characterized. By contrast, there are controversial reports about the expression and function of FcγRs in T cells. Here, we demonstrated that ~2% of resting CD4+ T cells express cell surface FcγRII (CD32). Analysis of CD32 expression in permeabilized cells revealed an increased proportion of CD4+CD32+ T cells (~9%), indicating that CD4+ T cells store a CD32 cytoplasmic pool. Activation of CD4+ T cells markedly increased the expression of CD32 either at the cell surface or intracellularly. Analysis of CD32 mRNA transcripts in activated CD4+ T cells revealed the presence of both, the stimulatory FcγRIIa (CD32a) and the inhibitory FcγRIIb (CD32b) isoforms of CD32, being the CD32a:CD32b mRNA ratio ~5:1. Consistent with this finding, we found not only that CD4+ T cells bind aggregated IgG, used as an IC model, but also that CD32 ligation by specific mAb induced a strong calcium transient in CD4+ T cells. Moreover, we found that pretreatment of CD4+ T cells with immobilized IgG as well as cross-linking of CD32 by specific antibodies increased both, the proliferative response of CD4+ T cells and the release of a wide pattern of cytokines (IL-2, IL-5, IL-10, IL-17, IFN-γ, and TNF-α) triggered by either PHA or anti-CD3 mAb. Collectively, our results indicate that ligation of CD32 promotes the activation of CD4+ T cells. These findings suggest that ICs might contribute to the perpetuation of chronic inflammatory responses by virtue of its ability to directly interact with CD4+ T cells through CD32a, promoting the activation of T cells into different inflammatory profiles.

Dampening of IL-2 Function in Infants With Severe Respiratory Syncytial Virus Disease.

Background: FOXP3+ regulatory T cells (Tregs) restrain the destructive potential of the immune system. We have previously reported a pronounced reduction in circulating Tregs in infants with severe respiratory syncytial virus (RSV) disease. Because interleukin-2 (IL-2) is critical for Treg growth, survival, and activity, we here analyzed IL-2 production and function in RSV-infected infants. Methods: Phenotype, proliferation, IL-2 production, and IL-2 signaling in CD4+ T cells were analyzed by flow cytometry. Serum soluble CD25 levels were quantified by ELISA. Results: CD4+ T cells from RSV-infected infants produced lower amounts of IL-2 and showed a reduced proliferative response compared with healthy infants. IL-2 increased CD4+ T-cell proliferation and FOXP3 expression in both healthy and RSV-infected infants. However, although IL-2 induced a similar pattern of STAT5 phosphorylation, the proliferative response of CD4+ T cells and the expression of FOXP3+ remained significantly lower in RSV-infected infants. Interestingly, we found a negative correlation between disease severity and both the production of IL-2 by CD4+ T cells and the ability of exogenous IL-2 to restore the pool of FOXP3+CD4+ T cells. Conclusions: A reduced ability to produce IL-2 and a limited response to this cytokine may affect the function of CD4+ T cells in RSV-infected infants.

Respiratory Syncytial Virus (RSV) Infects CD4+ T Cells: Frequency of Circulating CD4+ RSV+ T Cells as a Marker of Disease Severity in Young Children.

BACKGROUND: Although human airway epithelial cells are the main target of respiratory syncytial virus (RSV), it also infects immune cells, such as macrophages and B cells. Whether T cells are permissive to RSV infection is unknown. We sought to analyze the permissiveness of CD4+ T cells to RSV infection. METHODS: CD4+ and CD8+ T cells from cord blood, healthy young children, and adults were challenged by RSV or cocultured with infected HEp-2 cells. Infection, phenotype, and cytokine production by T cells were analyzed by flow cytometry or enzyme-linked immunosorbent assay. Expression of RSV antigens by circulating CD4+ T cells from infected children was analyzed by flow cytometry, and disease severity was defined by standard criteria. RESULTS: CD4+ and CD8+ T cells were productively infected by RSV. Infection decreased interleukin 2 and interferon γ production as well as the expression of CD25 and Ki-67 by activated CD4+ T cells. Respiratory syncytial virus antigens were detected in circulating CD4+ and CD8+ T cells during severe RSV infection of young children. Interestingly, the frequency of CD4+ RSV+ T cells positively correlated with disease severity. CONCLUSIONS: Respiratory syncytial virus infects CD4+ and CD8+ T cells and compromises T-cell function. The frequency of circulating CD4+ RSV+ T cells might represent a novel marker of severe infection.

Host response to respiratory syncytial virus infection.

PURPOSE OF REVIEW: Respiratory syncytial virus (RSV) infection is the leading cause of bronchiolitis and hospitalization in young infants and causes 100, 000-200, 000 deaths annually. There is still no licensed vaccine against RSV infection and the therapeutic options are mainly supportive. Despite almost six decades of research, important knowledge gaps remain with respect to the characterization of immune mechanisms responsible for protection and pathogenesis, as well as to the identification of risk factors that predict the severity of infection. RECENT FINDINGS: Observations made in mouse models and young children suggest that the early innate immune response plays a major role in the pathogenesis of bronchiolitis due to RSV infection. Recent studies have improved our understanding of the role of the adaptive immune response mediated by TH1, TH2, TH17, regulatory T cells, and CD8 T cells in the pathogenesis and resolution of RSV infection. Moreover, investigations performed in the last years have made important contributions to our knowledge of the immune response in young children, the principal risk group for severe disease. SUMMARY: A comprehensive understanding of how the protective and deleterious immune response during the course of RSV infection is induced in young children remains a challenge over the coming years.

Epithelial cells activate plasmacytoid dendritic cells improving their anti-HIV activity.

Plasmacytoid dendritic cells (pDCs) play a major role in anti-viral immunity by virtue of their ability to produce high amounts of type I interferons (IFNs) and a variety of inflammatory cytokines and chemokines in response to viral infections. Since recent studies have established that pDCs accumulate at the site of virus entry in the mucosa, here we analyzed whether epithelial cells were able to modulate the function of pDCs. We found that the epithelial cell lines HT-29 and Caco-2, as well as a primary culture of human renal tubular epithelial cells (HRTEC), induced the phenotypic maturation of pDCs stimulating the production of inflammatory cytokines. By contrast, epithelial cells did not induce any change in the phenotype of conventional or myeloid DCs (cDCs) while significantly stimulated the production of the anti-inflammatory cytokine IL-10. Activation of pDCs by epithelial cells was prevented by Bafilomycin A1, an inhibitor of endosomal acidification as well as by the addition of RNase to the culture medium, suggesting the participation of endosomal TLRs. Interestingly, the cross-talk between both cell populations was shown to be associated to an increased expression of TLR7 and TLR9 by pDCs and the production of LL37 by epithelial cells, an antimicrobial peptide able to bind and transport extracellular nucleic acids into the endosomal compartments. Interestingly, epithelium-activated pDCs impaired the establishment of a productive HIV infection in two susceptible target cells through the stimulation of the production of type I IFNs, highlighting the anti-viral efficiency of this novel activation pathway.

Mouse bone marrow-derived mesenchymal stromal cells turn activated macrophages into a regulatory-like profile.

In recent years it has become clear that the therapeutic properties of bone marrow-derived mesenchymal stromal cells (MSC) are related not only to their ability to differentiate into different lineages but also to their capacity to suppress the immune response. We here studied the influence of MSC on macrophage function. Using mouse thioglycolate-elicited peritoneal macrophages (M) stimulated with LPS, we found that MSC markedly suppressed the production of the inflammatory cytokines TNF-alpha, IL-6, IL-12p70 and interferon-gamma while increased the production of IL-10 and IL-12p40. Similar results were observed using supernatants from MSC suggesting that factor(s) constitutively released by MSC are involved. Supporting a role for PGE(2) we observed that acetylsalicylic acid impaired the ability of MSC to inhibit the production of inflammatory cytokines and to stimulate the production of IL-10 by LPS-stimulated M. Moreover, we found that MSC constitutively produce PGE2 at levels able to inhibit the production of TNF-alpha and IL-6 by activated M. MSC also inhibited the up-regulation of CD86 and MHC class II in LPS-stimulated M impairing their ability to activate antigen-specific T CD4+ cells. On the other hand, they stimulated the uptake of apoptotic thymocytes by M. Of note, MSC turned M into cells highly susceptible to infection with the parasite Trypanosoma cruzi increasing more than 5-fold the rate of M infection. Using a model of inflammation triggered by s.c. implantation of glass cylinders, we found that MSC stimulated the recruitment of macrophages which showed a low expression of CD86 and the MHC class II molecule Ia(b) and a high ability to produce IL-10 and IL-12p40, but not IL-12 p70. In summary, our results suggest that MSC switch M into a regulatory profile characterized by a low ability to produce inflammatory cytokines, a high ability to phagocyte apoptotic cells, and a marked increase in their susceptibility to infection by intracellular pathogens.