Impact of Pre-existing Cross-Reactive Antibodies on Cyclic Dengue Outbreaks in the Hyperendemic Region of Bali, Indonesia.

The four serotypes of the dengue virus (DENV) cause a range of diseases ranging from mild fever to severe conditions. Understanding the immunological interactions among the four serotypes is crucial in comprehending the dynamics of serotype shifting during outbreaks in areas where all four serotypes co-circulate. Hence, we evaluated the neutralizing antibody and antibody-dependent enhancement responses against the four DENV serotypes using acute-phase plasma samples collected from 48 laboratory-confirmed dengue patients during a dengue outbreak in Bali, Indonesia in 2022. Employing single-round infectious particles to exclusively investigate immunogenicity to the structural surface proteins of DENV, which are the targets of antibodies, we found that individuals with a probable prior history of DENV-1 infection exhibited increased susceptibility to secondary DENV-3 infection, attributed to cross-reactive antibodies with limited neutralizing activity against DENV-3 (geometric mean 50% neutralization titer (GMNT50) = 47.6 ± 11.5). This susceptibility was evident in vitro, with a mean fold enhancement of 28.4 ± 33.9. Neutralization titers against DENV-3 were significantly lower compared to other serotypes (DENV-1 GMNT50 = 678.1 ± 9.0; DENV-2 GMNT50 = 210.5 ± 8.7; DENV-4 GMNT50 = 95.14 ± 7.0). We demonstrate that prior immunity to one serotype provides limited cross-protection against the other serotypes, influencing the dominant serotype in subsequent outbreaks. These findings underscore the complexity of dengue immunity and its implications for vaccine design and transmission dynamics in hyperendemic regions.

The safety of recombinant human hyaluronidase PH20 in nonclinical models: An overview of toxicology, pharmacology, and impact of anti-PH20 antibodies.

Hyaluronan (HA) is a glycosaminoglycan that forms a gel-like barrier in the subcutaneous (SC) space, limiting bulk fluid flow and the dispersion of SC-administered therapeutics. Recombinant human hyaluronidase PH20 (rHuPH20) facilitates the rapid delivery of co-administered therapeutics by depolymerizing HA in the SC space. Administration of rHuPH20 can induce the formation of anti-rHuPH20 antibodies, or anti-drug antibodies (ADAs), with the potential to bind endogenous PH20 hyaluronidase in the adult testes and epididymis. Using a variety of relevant animal models and multiple dose regimens of rHuPH20 across the full spectrum of animal development, we demonstrated that rHuPH20 administration resulted in the formation of ADAs. Although these ADAs can bind both the recombinant rHuPH20 enzyme and recombinant versions of animal model-specific hyaluronidases, they had no impact on fertility parameters (as measured by sperm concentration and motility, litter size, and litter viability) or fetal development. We present the result of our nonclinical studies in order of the developmental lifecycle, beginning with adults. Toxicology studies that extend beyond the standard package are also presented. These studies demonstrate the favorable safety profile of rHuPH20 and ADAs in nonclinical models. Additionally, we identified substantial safety margins for therapeutically relevant doses of rHuPH20.

Case Report: two cases of anti-neutrophil cytoplasmic antibody-associated vasculitis involving large vessels.

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of systemic diseases caused by a combination of many factors, including genetics, environment, and immunity. AAV is characterized by predominantly small-vessel involvement and has a variety of clinical manifestations. Small-vessel lesions of the kidneys and lungs are common, and lesions of medium-sized arteries may also present, but the involvement of large arteries and their primary branches is very rare. This report delineates two instances of AAV with large arterial involvement, one case presenting with lesions of the aortic valve and the other with lesions of the pulmonary artery. The first case involved a 57-year-old man with no underlying diseases. Transthoracic echocardiography showed thickening of the left and right coronary valves of the aortic valve with enhanced echogenicity, moderate echogenic masses were seen on both valve leaflets, and the leaflets had restricted opening and poor closure. Blood tests showed positive perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA) and anti-myeloperoxidase (MPO) antibodies. The patient's aortic valve thickening virtually disappeared after treatment with hormones combined with immunosuppressive agents. The second case involved a 60-year-old woman whose transthoracic echocardiography and CT (computed tomography) angiography of the pulmonary arteries showed wall thickening of the main pulmonary artery and the proximal left and right pulmonary arteries, leading to luminal stenosis. Blood tests showed positive cytoplasmic anti-neutrophil cytoplasmic antibodies (c-ANCA) and anti-proteinase 3 (PR 3) antibodies. The patient's pulmonary artery wall thickening reduced after receiving hormones in combination with immunosuppression but she died of heart failure during subsequent treatment. The patient had been diagnosed with tuberculosis six months earlier and had been poorly treated with anti-tuberculosis therapy. The involvement of large arteries in AAV is a rare and critical condition with rapid progression and a high mortality rate. Early recognition of this type of AAV and aggressive immunosuppressive therapy may facilitate the reversal of the vascular lesion and a reduction in the risk of patient death.

Development of systemic and mucosal immune responses against gut microbiota in early life and implications for the onset of allergies.

The early microbial colonization of human mucosal surfaces is essential for the development of the host immune system. Already during pregnancy, the unborn child is prepared for the postnatal influx of commensals and pathogens via maternal antibodies, and after birth this protection is continued with antibodies in breast milk. During this critical window of time, which extends from pregnancy to the first year of life, each encounter with a microorganism can influence children's immune response and can have a lifelong impact on their life. For example, there are numerous links between the development of allergies and an altered gut microbiome. However, the exact mechanisms behind microbial influences, also extending to how viruses influence host-microbe interactions, are incompletely understood. In this review, we address the impact of infants' first microbial encounters, how the immune system develops to interact with gut microbiota, and summarize how an altered immune response could be implied in allergies.

Stiff-person syndrome in association with Hashimoto's thyroiditis: a case report.

Stiff-person syndrome (SPS) is a rare neurological disorder characterized by chronic and progressive axial muscle rigidity and paroxysmal painful muscle spasms. The present case study described an SPS patient (increased anti-GAD65 antibody in serum and cerebrospinal fluid) with co-occurring Hashimoto's thyroiditis and decreased C3 complement levels. The clinical presentation, diagnostic approach, and treatment employed for this unique case were comprehensively described in detail. In this case, we comprehensively presented a case of SPS with co-occurring Hashimoto's thyroiditis and an associated decrease in serum C3 complement, as well as a discussion on the current data on this topic.

Incidence of Persistence and Recurrence of Differentiated Thyroid Cancer in Post-surgical Cases From a Tertiary Care Hospital in Dubai, United Arab Emirates.

Background Despite the excellent prognosis of differentiated thyroid carcinoma, recurrence remains a major concern. However, the persistence of thyroid cancer post-thyroidectomy is not uncommon. We aimed to characterise patients who underwent re-operative surgery for differentiated thyroid carcinoma and analyse the percentage of re-operations that truly were for "recurrent" disease versus the management of persistent disease. Methods We conducted a retrospective review of the hospital database, analysing patients who visited the nuclear medicine department at Mediclinic City Hospital, a tertiary care hospital in Dubai, United Arab Emirates, between 2015 and 2022. The study included patients with differentiated thyroid carcinoma who underwent re-operations after total thyroidectomy. Recurrence was defined as the development of disease after a patient had undetectable thyroglobulin and negative radiological scans within one year of the first surgery. Cases were categorised as "recurrent", "persistent", or "unable to classify" in the event of missing data. Results Out of 836 patients diagnosed with differentiated thyroid carcinoma who visited the nuclear medicine department, 71 underwent re-operations. The mean age of these patients was 44.4 years (CI 41.7-47.0), of whom 78.9% were females. Almost half (46.5%) underwent re-operations within the first year, and 98.6% were diagnosed with papillary thyroid carcinoma. We were able to classify 63.4% of cases (n=45) as persistent disease, while 24 cases were categorised as "unable to classify". Only two cases met the criteria for recurrent disease. Conclusion The majority of cases previously classified as "recurrent" in differentiated thyroid carcinoma were found to be a persistent disease, possibly indicating inadequate therapy. Further research may be required to explore the reasons behind this eye-opening rate of disease persistence. This highlights an area for improvement in the management and future outcomes of differentiated thyroid carcinoma patients.

Use of Adjuvant Compositions Based on Squalene Ensures Induction of Neutralizing Antibodies against SARS-CoV-2.

Squalene-based adjuvant compositions that can provide effective induction of specific humoral immune response have been developed. Recombinant receptor-binding domain (RBD) of surface S-protein of SARS-CoV-2 was used to evaluate the properties of the composition. Immunization of mice with the developed squalene-based compositions in combination with RBD allows obtaining high titers of specific antibodies: from 105 to 2×106. The blood sera from immunized mice exhibit neutralizing activity against SARS-CoV-2 Delta variant (B.1.617.2) with a titer up to 1:2000.

Considerations for the development of monoclonal antibodies to address new viral variants in COVID-19.

INTRODUCTION: Monoclonal antibody (mAb) therapies proved safe and effective in preventing progression of COVID-19 to hospitalization, but most were eventually defeated by continued viral evolution. mAb combinations and those mAbs that were deliberatively selected to target conserved regions of the SARS-CoV-2 spike protein proved more resilient to viral escape variants as evident by longer clinical useful lives. AREAS COVERED: We searched PubMed for literature covering the need, development and use of mAb therapies for COVID-19. As much of humanity now has immunity to SARS-CoV-2, the population at most risk is that of immunocompromised individuals. Hence, there continues to be a need for mAb therapies for immunocompromised patients. However, mAb use in this population carries the risk for selecting mAb-resistant variants, which could pose a public health concern if they disseminate to the general population. EXPERT OPINION: Going forward, structural knowledge of the interactions of Spike with its cellular receptor has identified several regions that may be good targets for future mAb therapeutics. A focus on designing variant-resistant mAbs together with cocktails that target several epitopes and the use of other variant mitigating strategies such as the concomitant use of small molecule antivirals and polyclonal preparations could extend the clinical usefulness of future preparations.

Anti-carbamylated Protein Antibodies Positivity in Rheumatoid Arthritis and Its Association With Rheumatoid Factor and Anti-cyclic Citrullinated Protein Antibodies.

Background Rheumatoid arthritis (RA) is a widespread autoimmune disease affecting millions of people worldwide. The current markers include anti-cyclic citrullinated peptide (anti-CCP) antibodies and rheumatoid factor (RF), which are nonspecific and elevated in various conditions and do not have a prognostic value. They are also elevated in the later stages of the disease. Anti-carbamylated protein (anti-CarP) antibodies have been reported to be associated with joint damage in RA. Therefore, this study aimed to evaluate the sensitivity and specificity of anti-CarP antibodies in individuals with RA and their relationship with inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). Methods This was a cross-sectional case-control study conducted from April 2020 to March 2021 at the Saveetha Medical College, Chennai, India. The age makeup of the three groups was evaluated: Group 1 comprised anti-CCP and RF-positive patients; Group 2 comprised anti-CCP and RF-negative patients; and Group 3 was the control group, which comprised healthy volunteers. Patient samples, including blood and serum, have been utilized to conduct various assessments aimed at evaluating biomarkers such as CRP, ESR, RF, and autoantibodies like anti-CCP and anti-CarP. Results This study examined the role of various autoantibodies and biomarkers in RA across three distinct groups. Group 1 predominantly consisted of middle-aged individuals, and women constituted the majority in both Group 1 and Group 2, consistent with higher RA prevalence among females. In Group 1, 65.7% of patients tested positive for anti-CarP, while in Group 2, 48.6% tested positive even when RF and anti-CCP antibodies were absent. This suggests a potential diagnostic role for anti-CarP antibodies in identifying RA patients early. CRP and ESR levels were significantly elevated in RA patients (Groups 1 and 2) compared to healthy controls (Group 3), indicating higher inflammatory activity in affected individuals. We also observed that anti-CarP antibodies had a specificity of 69.1% and a sensitivity of 78.2%. Positive correlations between the diagnosis of RA and anti-CarP antibody positivity were observed across the groups and correlated well with the inflammatory markers and signs such as joint damage. The data were found to be statistically significant. Conclusions Our study showed a significant correlation between joint damage and CRP levels and a positive correlation between anti-CarP antibodies and ESR and CRP values. These findings suggest that anti-CarP antibodies can offer certain advantages over RF and anti-CCP antibodies in RA diagnosis due to their early detection potential, higher specificity, complementary diagnostic role, and predictive value for disease severity.

Comparison of clinical and serological features in thrombotic antiphospholipid syndrome patients, with and without associated systemic lupus erythematosus, followed for up to 42 years: A single centre retrospective study.

OBJECTIVE: To assess the impact of concomitant systemic lupus erythematosus (SLE) on the clinicopathological manifestations of thrombotic antiphospholipid syndrome (APS). METHODS: This single-centre, retrospective study compared clinical and antiphospholipid antibody (aPL) data from 118 patients, 58 with SLE-associated APS (SLE-APS), and 60 with primary APS. RESULTS: Median follow-up was 13.9 (IQR 7.7-19.3) and 8.6 years (3.5-10.6) for the SLE-APS cohort and PAPS cohort, respectively. Age at diagnosis of APS was lower in the SLE-APS cohort (mean 35.9 vs PAPS: 46.7 years; p < 0.05). Distribution of aPL subtypes was similar across cohorts. 198 thrombotic events were identified overall (index plus recurrent), with venous thromboembolism (VTE) and arterial thrombosis each occurring in just over half of patients in both cohorts. Microvascular thrombosis (12.1% vs 0%), and a mixed (any combination of venous, arterial and microvascular) thrombotic phenotype (19.0% vs 6.7%, p = 0.05) were more prevalent in SLE-APS patients. Recurrent thrombosis incidence rates (∼0.5 events/10-patient years), and Kaplan-Meier recurrence-free survival after index thrombosis, were similar. In the PAPS cohort, only: (i) triple-aPL-positivity was associated with a significantly higher recurrent thrombosis event rate (incidence rate ratio 2.22, p = 0.03) and lower recurrence-free survival after first thrombosis (log-rank test p = 0.01); (ii) lupus anticoagulant (LA)-positivity was associated with higher prevalance of arterial thrombosis (RR 2.69, p = 0.01), and lower prevlance of VTE (RR 0.48, p < 0.001), versus LA-negativity. CONCLUSION: Concomitant SLE does not appear to modify long-term recurrent thrombosis risk, or aPL phenotypes, in patients with APS. Triple-aPL-positivity and LA-positive status may have less influence on thrombotic outcomes in patients with SLE-APS compared to PAPS.

Control of Coxiella burnetii shedding in a dairy goat herd by annual offspring vaccination.

A Coxiella burnetii vaccination program, targeting only doelings, was introduced on a German goat farm to curb bacterial shedding. In 2018, adults were vaccinated with a C. burnetii Phase I vaccine at three-weeks apart following pathogen diagnosis, with a booster administered six months later due to sustained high shedding. From 2018 to 2021, doelings received two vaccine doses without any further boosters. To assess the program's efficacy, vaginal swabs from up to 40 animals per age group were collected during kidding seasons from 2019 to 2022. Bulk tank milk (BTM) samples were gathered monthly from January 2018 to October 2022 to monitor herd-level shedding. Real-time PCR analysis determined genome equivalents in all three sample types. Serum samples were taken before the initial immunization and during the post-kidding season from up to 40 goats per age group annually from 2018 to 2022. Phase-specific ELISAs determined IgG Phase I and Phase II antibodies. Additionally, two serum samples per age group from 2022 were analyzed using a neutralization assay. A few goats continued shedding small quantities during subsequent kidding seasons. Although positive BTM samples decreased, they displayed an undulating trend. Most age groups exhibited robust IgG Phase I responses and lower IgG Phase II levels post immunization. Mean IgG levels remained elevated until the study ended compared to pre-vaccination levels in most age groups. Additionally, neutralizing antibodies were present regardless of IgG response. Overall, double vaccination induced lasting antibody levels, but did not entirely prevent C. burnetii shedding. The resilience of the observed humoral immune activity requires further investigation.

Detection of anti-HCV antibodies and risk factors in a population with access to public healthcare in Mexico.

INTRODUCTION AND AIM: Timely detection and diagnosis of hepatitis C virus (HCV) involves identifying the population that is predisposed to treatment and prevention, thus limiting complications and preventing infection. The aim of this study was to analyze and describe risk factors associated with anti-HCV antibody detection in a population with access to public healthcare that participated in a national screening program. MATERIAL AND METHODS: An analytic cross-sectional study was conducted that utilized data related to rapid tests carried out between September 2021 and October 2022 in 26 of the 32 states of Mexico. Anti-HCV reactive tests were selected, according to age and sex, for analyzing and comparing possible risk factors through descriptive and inferential statistics. The geographic distribution and density of the screening program at the state and municipal levels was analyzed. RESULTS: There were 75,185 anti-HCV antibody detections, 2,052 reactive tests, and mean participant age was 44.3 years (±15.1). Occupation: 32.3% were employees, 19% were housewives, and 18.2% were healthcare workers. Five out of every 10 cases had no indication of risk factors, but there was a 1.4 and 5-times greater likelihood of anti-HCV detection in men with a history of sharps injury or intravenous psychoactive substance use, compared with women. Regarding place of residence, 80% of the reactive tests were concentrated in the State of Mexico, Mexico City, and Guanajuato. CONCLUSIONS: The evidence herein helps determine the population and risk factors that should be focused on in carrying out the HCV microelimination strategy of continuous screening, diagnosis, medical treatment access, and epidemiologic surveillance.

Chimeric HLA antibody receptor T cell therapy for humoral transplant rejection.

Antibody-mediated rejection (ABMR) is a significant obstacle to achieving optimal long-term outcomes after solid organ transplantation. The presence of donor-specific antibodies (DSA), particularly against HLA, increases the risk of allograft rejection and subsequent graft loss. No effective treatment of ABMR currently exists, warranting novel approaches to target the HLA-specific humoral alloimmune response. Cellular therapies may hold promise to this end. According to publicly available sources as of now, three independent laboratories have genetically engineered a chimeric HLA-antibody receptor (CHAR) and transduced it into human T cells, based on the demonstrated efficacy of chimeric antigen receptor T cell therapies in malignancies. These CHAR-T cells are designed to exclusively eliminate B cells that produce donor-specific HLA antibodies, which form the cornerstone of ABMR. CHAR technology generates potent and functional human cytotoxic T cells to target alloreactive HLA-specific B cells, sparing B cells with other specificities. Thus, CHAR technology may be used as a selective desensitization protocol and to treat antibody-mediated rejection after solid organ transplantation.

Denosumab: A Useful Addition to the Armamentarium for the Management of Male Osteoporosis.

Bone is a dynamic tissue. It remodels, preserving serum calcium, repairing microdamage, and maintaining strength. Osteoporosis is caused by a decrease in bone strength, which manifests clinically as low-energy vertebral and non-vertebral fractures. Osteoporosis poses a significant public health challenge. While it's often portrayed as primarily impacting postmenopausal women, there's been growing recognition among researchers and clinicians regarding its prevalence in men. Major fracture in men has higher mortality rates than in women. Denosumab is a fully human monoclonal immunoglobulin G2 (IgG2) antibody that binds to RANKL, the principal regulator of osteoclastic bone resorption. Multiple studies suggest that denosumab is both effective and safe, exhibiting higher adherence rates and greater patient satisfaction. In this narrative review, we highlighted the effects of denosumab in men with osteoporosis, subsequent changes in bone mineral density, and bone turnover markers outlining the literature and guideline support.

Progress and Remaining Opportunities to Increase the Use of Animal-free Antibodies in the USA.

The scientific and ethical issues associated with the use of animal-derived antibodies in research can be overcome by the use of animal-free, sequence-defined recombinant antibodies, whose benefits are well documented. Here, we describe progress made following a 2019 expert meeting focused on improving the quality and reproducibility of biomedical research by accelerating the production and use of animal-free recombinant antibodies in the USA. In the five intervening years since the meeting, participants have established multifaceted initiatives to tackle the next steps outlined during the meeting. These initiatives include: prioritising the replacement of ascites-derived and polyclonal antibodies; distributing educational materials describing recombinant antibodies; fostering public-private partnerships to increase access to recombinant antibodies; and increasing the availability of funding for recombinant antibody development. Given the widescale use of antibodies across scientific disciplines, a transition to modern antibody production methods relies on a commitment from government agencies, universities, industry and funding organisations, to initiatives such as those outlined here.

A qualitative investigation of the experiences of patients living with antiphospholipid antibodies.

OBJECTIVE: Substantial morbidity and mortality affect those with antiphospholipid antibodies (aPLs) and antiphospholipid syndrome (APS), yet patient experiences remain poorly understood. This research investigated patient experiences of aPL/APS diagnosis; effects on daily life; and healthcare and treatment. METHODS: Patients aged ≥18 years with APS per the Revised Sapporo criteria or with ≥1 positive aPL on ≥2 occasions were recruited from a Canadian multidisciplinary APS clinic to participate in semi-structured in-depth interviews. Interviews were conducted virtually and transcribed verbatim for subsequent thematic analysis. RESULTS: Twenty-one patients with aPLs/APS participated; 95.2% were female, mean (SD) age was 45.6 (15.0) years. Most (71.4%) had APS, and 71.4% had aPLs/APS with SLE. Results are presented around patient experiences of aPL/APS diagnosis, effects on daily life, and healthcare and treatment. Participants described medical complications/physical symptoms and the healthcare, lifestyle, and emotional impacts experienced around the time of aPLs/APS diagnosis. In addition to the physical and psychosocial impacts of living with aPLs/APS, patients reported modified leisure activities, altered employment trajectories, and positive and negative impacts on relationships. Impacts on family planning were also a critical component of the aPL/APS lived experience; participants shared experiences of miscarriage, other pregnancy complications, and medication-related challenges (e.g., with low-molecular-weight heparin injections). Challenging aspects of aPL/APS healthcare and treatment were also discussed, particularly related to the lifestyle, physical, and emotional burden of medication use. Although a lack of resources was described, participants expressed trust in healthcare providers when making management decisions or when seeking information. Suggestions for resources included the need for additional medication-related information, examples to help contextualize management behaviours, and additional information for those with aPLs/APS without SLE. CONCLUSION: Patients highlighted how the diverse manifestations of aPLs/APS, accentuated by management-related challenges, impose considerable physical and psychosocial burdens. Results will inform the development of patient resources aligned with patient priorities.

Neonatal lupus erythematosus presenting with effusions: A 13-year retrospective study.

OBJECTIVES: Neonatal systemic lupus erythematosus (NLE) is an acquired autoimmune disease. The presence of effusions, such as pleural effusion and pericardial effusion, is rare. The present study helped investigate the clinical characteristics and progression of children with NLE combined with effusions. METHODS: Clinical data of patients diagnosed with NLE were retrospectively collected and analyzed from January 1, 2011, to December 31, 2023, at the Children's Hospital of Soochow University and Suzhou Municipal Hospital. Patients with NLE were divided into effusion and non-effusion groups based on the presence of effusion. Moreover, the clinical data of the newborns in both groups were compared and investigated. RESULTS: Eleven (11/45, 24.44%) NLE patients had effusions, such as pleural effusion, testicular hydrocele, peritoneal effusion, pericardial effusion, and hydrocephalus. Other organs involved in effusion patients were cutaneous, gastrointestinal, hematologic, cardiac, and neurological. Among the patients with effusion, five cases of SLE in pregnant mothers, two cases of Sjogren's syndrome, one case of photoallergic symptoms, and three of pregnant mothers with no history of antenatal autoimmune disease. Pregnant mother' autoimmune disease in remission prior to pregnancy, or stable low disease activity. Seven patients were positive for Anti-SSA, five of which were double positive for Anti-SSA and Anti-SSB. Compared with the non-effusion group, the effusion group patients had significantly higher lactate dehydrogenase, creatine kinase, and fibrinogen, significantly lower platelets, total protein, and albumin. These patients were likelier to have thrombocytopenia and coagulation abnormalities. Logistics regression analysis demonstrated that NLE patients with effusions are more likely to have decreased serum total protein levels. All NLE patients with effusion have self-resorption of the effusion. CONCLUSIONS: 24.44% of patients had effusions in our study. NLE patients with effusion are more likely to have hematologic involvement and a more inflammatory response. The effusion in NLE patients is usually self-resorption, severe cases can be treated with nonsteroidal anti-inflammatory drugs/steroids. Key Points • NLE patients combined with effusions and were self-limiting, with pleural effusion being the most common. • NLE patients combined with effusions have a more inflammatory response, significant abnormalities in the blood routine and biochemical-related indexes.

ATP-P2X7R pathway activation limits the Tfh cell compartment during pediatric RSV infection.

Background: Follicular helper T cells (Tfh) are pivotal in B cell responses. Activation of the purinergic receptor P2X7 on Tfh cells regulates their activity. We investigated the ATP-P2X7R axis in circulating Tfh (cTfh) cells during Respiratory Syncytial Virus (RSV) infection. Methods: We analyzed two cohorts: children with RSV infection (moderate, n=30; severe, n=21) and healthy children (n=23). We utilized ELISA to quantify the levels of PreF RSV protein-specific IgG antibodies, IL-21 cytokine, and soluble P2X7R (sP2X7R) in both plasma and nasopharyngeal aspirates (NPA). Additionally, luminometry was employed to determine ATP levels in plasma, NPA and supernatant culture. The frequency of cTfh cells, P2X7R expression, and plasmablasts were assessed by flow cytometry. To evaluate apoptosis, proliferation, and IL-21 production by cTfh cells, we cultured PBMCs in the presence of Bz-ATP and/or P2X7R antagonist (KN-62) and a flow cytometry analysis was performed. Results: In children with severe RSV disease, we observed diminished titers of neutralizing anti-PreF IgG antibodies. Additionally, severe infections, compared to moderate cases, were associated with fewer cTfh cells and reduced plasma levels of IL-21. Our investigation revealed dysregulation in the ATP-P2X7R pathway during RSV infection. This was characterized by elevated ATP levels in both plasma and NPA samples, increased expression of P2X7R on cTfh cells, lower levels of sP2X7R, and heightened ATP release from PBMCs upon stimulation, particularly evident in severe cases. Importantly, ATP exposure decreased cTfh proliferative response and IL-21 production, while promoting their apoptosis. The P2X7R antagonist KN-62 mitigated these effects. Furthermore, disease severity positively correlated with ATP levels in plasma and NPA samples and inversely correlated with cTfh frequency. Conclusion: Our findings indicate that activation of the ATP-P2X7R pathway during RSV infection may contribute to limiting the cTfh cell compartment by promoting cell death and dysfunction, ultimately leading to increased disease severity.