Immune response to viscerotropic Leishmania: a comprehensive review.

L. donovani and L. infantum infections are associated with a broad clinical spectrum, ranging from asymptomatic cases to visceral leishmaniasis (VL) with high mortality rates. Clinical manifestations such as post-kala-azar dermal leishmaniasis (PKDL) and visceral leishmaniasis-associated hemophagocytic lymphohistiocytosis-mimic (VL-associated HLH-mimic) further contribute to the diversity of clinical manifestations. These clinical variations are intricately influenced by the complex interplay between the host's immune response and the parasite's escape mechanisms. This narrative review aims to elucidate the underlying immunological mechanisms associated with each clinical manifestation, drawing from published literature within the last 5 years. Specific attention is directed toward viscerotropic Leishmania sinfection in patients with inborn errors of immunity and acquired immunodeficiencies. In VL, parasites exploit various immune evasion mechanisms, including immune checkpoints, leading to a predominantly anti-inflammatory environment that favors parasite survival. Conversely, nearly 70% of individuals are capable of mounting an effective pro-inflammatory immune response, forming granulomas that contain the parasites. Despite this, some patients may experience reactivation of the disease upon immunosuppression, challenging current understandings of parasite eradication. Individuals living with HIV and those with inborn errors of immunity present a more severe course of infection, often with higher relapse rates. Therefore, it is crucial to exclude both primary and acquired immune deficiencies in patients presenting disease relapse and VL-associated HLH-mimic. The distinction between VL and HLH can be challenging due to clinical similarities, suggesting that the nosological entity known as VL-associated HLH may represent a severe presentation of symptomatic VL and it should be considered more accurate referring to this condition as VL-associated HLH-mimic. Consequently, excluding VL in patients presenting with HLH is essential, as appropriate antimicrobial therapy can reverse immune dysregulation. A comprehensive understanding of the immune-host interaction underlying Leishmania infection is crucial for formulating effective treatment and preventive strategies to mitigate the disease burden.

CD38high/HLA-DR+CD8+ T lymphocytes display pathogen-specific expansion regardless of hemophagocytic lymphohistiocytosis.

The characteristic expansion of T CD38high/HLA-DR+CD8+ lymphocytes observed in hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) proved able to distinguish HLH/MAS from sepsis and systemic juvenile idiopathic arthritis. However, the performance of this marker in differentiating HLH/MAS from other pediatric febrile conditions with similar clinical onset and yet entirely different treatments remains unexplored. CD38high/HLA-DR+CD8+ frequencies measured in the peripheral fresh blood of pediatric patients attended for suspicion of HLH/MAS were retrospectively recorded and clinical characteristics were retrieved. CD38high/HLA-DR+CD8+ frequencies in HLH/MAS patients (15 patients; median: 22.0%, IQR: 11.0-49.0%) were compared with those who presented febrile conditions other-than-HLH (28 patients; median: 13.0%, IQR: 3.9-28.7%; p = 0.24). HLH and non-HLH patients were subsequently regrouped based on the presence of an identified infection (22 patients; median: 27.0%, IQR: 15.2-72.1%) and compared with those without infections (21 patients; median: 7.6%, IQR: 3.7-24.3%; p = 0.0035). CD38high/HLA-DR+CD8+ percentages were significantly higher only in the infection group compared with the noninfection one, with a patent pathogen-specific expansion in Epstein-Barr virus primoinfection and visceral leishmaniasis regardless of the presence of HLH. CD38high/HLA-DR+CD8+ frequencies do not appear as an HLH-specific marker as they naturally expand in other clinical situations that are common in childhood and may mimic HLH initial presentation.

Seasonality and severity of respiratory syncytial virus during the COVID-19 pandemic: a dynamic cohort study.

OBJECTIVES: To investigate seasonality, epidemiologic characteristics, and clinical severity variations of respiratory syncytial virus (RSV)-associated hospitalizations following the easing of COVID-19 restrictions in Tuscany, Italy, up to the 2022-2023 season. METHODS: From 2017 to 2023, a dynamic cohort consisting of all resident children aged ≤2 years was followed up in regional registries. The person-time incidence rate of RSV-associated hospitalizations per 1,000 person-years and risk of severe hospitalization (intensive care unit, continuous positive airway pressure, or mechanical ventilation) per 100 RSV hospitalizations were calculated. RSV seasonality was investigated with retrospective methods. RESULTS: A total of 193,244 children were followed up. After the easing of restrictions, RSV epidemics showed earlier seasonality and shorter duration compared with pre-pandemic (2017 to 2019), with this deviation decreased in 2022-2023. In 2021-2022 and 2022-2023, the incidence rate of RSV-associated hospitalizations significantly increased compared with pre-pandemic (2022-2023 risk ratio 3.6, 95% confidence interval 3.3-4.0), with larger increases among older age groups. Among hospitalized children, only those aged ≥12 months showed an increased risk of severe hospitalization, particularly during 2021-2022 (risk ratio 4.7, 95% confidence interval 1.5-24.3). CONCLUSIONS: Our findings suggest a gradual return of RSV epidemics to the pre-pandemic pattern, although relevant increases in disease incidence persist. Reduced regular RSV exposure among older children may lead to declining immunity and increased severe outcome risks.

Effect of antimetabolite regimen on cellular and humoral immune response to SARS-COV-2 vaccination in solid organ transplant recipients.

OBJECTIVE: Novel mRNA-based vaccines have been proven to be powerful tools in combating the global pandemic caused by SARS-CoV-2 protecting individuals, especially the immunocompromised, from COVID-19. Still, it remains largely unknown how solid organ transplant and different immunosuppressive medications affect development of vaccine-induced immunity. METHODS: In this work, we monitored humoral and cellular memory responses after mRNA SARS-CoV-2 two-doses and booster doses vaccination in cystic fibrosis lung transplanted patients (CFT) and compared them with both cystic fibrosis patients without lung transplant (CF) and with kidney transplant recipients (KT). In particular, we investigated the effects of immunosuppressive regimens on immune memory to SARS-CoV-2 after mRNA SARS-CoV-2 vaccine in transplanted patients. RESULTS: Our results showed that immunocompromised transplanted patients displayed a weak cellular and humoral memory to SARS-CoV-2 mRNA vaccination. In addition, obtained data clearly demonstrate that immunosuppressive therapy regimen including antimetabolites, further reduces patients' ability to respond to vaccination at both humoral and cell-mediated level. Notably, patient treated with antimetabolites showed a lower humoral and cellular response also after a booster dose vaccination. CONCLUSION: These results, even if obtained on a small patient's cohort, question whether immunocompromised patients need interventions to improve vaccine SARS-CoV-2 mRNA vaccine response such as additional jab or modulation of immunosuppressive therapy.

Epidemiology of respiratory syncytial virus in hospitalized children over a 9-year period and preventive strategy impact.

Background: Respiratory Syncytial Virus (RSV) is the primary cause of respiratory infections and hospitalizations in young children globally, leading to substantial disease burden and mortality. The aim of the present study was to review and provide updates on how the SARS-CoV-2 pandemic have significantly influenced RSV epidemiology on hospitalized children due to RSV infection. A potential impact of the available preventive strategies on the same population were provided. Methods: All children aged 0-6 years hospitalized at Meyer Children's Hospital IRCCS for RSV infection from September 2014 to March 2023 were retrospectively recorded. Seasonal trends before and after SARS-CoV-2 pandemic, age distribution, ICU admission and co-infections, comorbidities and prematurity were retrieved. Predictions on the number of hospitalizations avoided by the deployment of different preventive strategies were provided. Results: A total of 1,262 children with RSV infection were included in the study. The 70% of them had less than 1 year-of-age at the moment of hospitalization and almost 50% less than 3 months. In the post-pandemic seasons, a 317% increase in the number of hospitalizations was recorded with a significant increase in older children compared to the pre-pandemic seasons. ICU support was required for 22% of children, the majority of whom were under 3 months of age. Almost 16% of hospitalized children were born preterm and only 27% of hospitalized children had prior comorbidities. The rate of comorbidities among RSV hospitalized children increased with age. Nirsevimab prophylaxis could have prevented more than 46% of hospitalizations in this cohort. A preventive strategy addressing also children aged 7 months to 6 years of age with co-existing comorbidities would increase that rate above 57%. Discussion: The identification of RSV hospitalization-related features is informing the decision-maker for the deployment of the wisest preventive approach on a population scale.

Convergence and divergence in Kawasaki disease and multisystem inflammatory syndrome in children: results from the COVASAKI survey.

OBJECTIVES: To compare Kawasaki disease (KD) and multisystem inflammatory syndrome (MIS-C) in children. METHODS: Prospective collection of demographics, clinical and treatment data. Assessment of type 1 interferon (IFN) score, CXCL9, CXCL10, Interleukin (IL)18, IFNγ, IL6, IL1b at disease onset and at recovery. RESULTS: 87 patients (43 KD, 44 MIS-C) were included. Age was higher in MIS-C compared to KD group (mean 31±23 vs. 94±50 months, p<0.001). Extremities abnormalities (p=0.027), mucosal involvement (p<0.001), irritability (p<0.001), gallbladder hydrops (p=0.01) and lymphadenopathy (p=0.07) were more often recorded in KD. Neurological findings (p=0.002), gastrointestinal symptoms (p=0.013), respiratory involvement (p=0.019) and splenomegaly (p=0.026) were more frequently observed in MIS-C. Cardiac manifestations were higher in MIS-C (p<0.001), although coronary aneurisms were more frequent in KD (p=0.012). In the MIS-C group, the multiple linear regression analysis revealed that a higher IFN score at onset was related to myocardial disfunction (p<0.001), lymphadenopathy (p=<0.001) and need of ventilation (p=0.024). Both CXCL9 and CXCL10 were related to myocardial disfunction (p<0.001 and p=0.029). IL18 was positively associated to PICU admission (0.030) and ventilation (p=004) and negatively associated to lymphadenopathy (0.004). IFNγ values were related to neurological involvement and lymphadenopathy (p<0.001), IL1b to hearth involvement (0.006). A negative correlation has been observed between IL6 values, heart involvement (p=0.013) and PICU admission (p<0.001). CONCLUSIONS: The demographic and clinical differences between KD e MIS-C cohorts confirm previous reported data. The assessment of biomarkers levels at MIS-C onset could be useful to predict a more severe disease course and the development of cardiac complications.

Corrigendum: HLH as an additional warning sign of inborn errors of immunity beyond familial-HLH in children: a systematic review.

[This corrects the article DOI: 10.3389/fimmu.2024.1282804.].

Immunological Aspects of Kabuki Syndrome: A Retrospective Multicenter Study of the Italian Primary Immunodeficiency Network (IPINet).

Kabuki Syndrome (KS) is a multisystemic genetic disorder. A portion of patients has immunological manifestations characterized by increased susceptibility to infections and autoimmunity. Aiming to describe the clinical and laboratory immunological aspects of KS, we conducted a retrospective multicenter observational study on patients with KS treated in centers affiliated to the Italian Primary Immunodeficiency Network.Thirty-nine patients were enrolled, with a median age at evaluation of 10 years (range: 3 m-21y). All individuals had organ malformations of variable severity. Congenital heart defect (CHD) was present in 19/39 patients (49%) and required surgical correction in 9/39 (23%), with associated thymectomy in 7/39 (18%). Autoimmune cytopenia occurred in 6/39 patients (15%) and was significantly correlated with thymectomy (p < 0.002), but not CHD. Individuals with cytopenia treated with mycophenolate as long-term immunomodulatory treatment (n = 4) showed complete response. Increased susceptibility to infections was observed in 22/32 patients (69%). IgG, IgA, and IgM were low in 13/29 (45%), 13/30 (43%) and 4/29 (14%) patients, respectively. Immunoglobulin substitution was required in three patients. Lymphocyte subsets were normal in all patients except for reduced naïve T-cells in 3/15 patients (20%) and reduced memory switched B-cells in 3/17 patients (18%). Elevated CD3 + TCRαß + CD4-CD8-T-cells were present in 5/17 individuals (23%) and were correlated with hematological and overall autoimmunity (p < 0.05).In conclusion, immunological manifestations of KS in our cohort include susceptibility to infections, antibody deficiency, and autoimmunity. Autoimmune cytopenia is correlated with thymectomy and elevated CD3 + TCRαß + CD4-CD8-T-cells, and benefits from treatment with mycophenolate.

Expanded Newborn Screening for Inborn Errors of Immunity: The Experience of Tuscany.

BACKGROUND: Inborn errors of immunity (IEIs) include 485 inherited disorders characterized by an increased susceptibility to life-threatening infectious diseases, autoimmunity, and malignant diseases with a high mortality rate in the first years of life. Severe combined immunodeficiency is the most severe of the IEIs, and its detection should be a primary goal in a newborn screening (NBS) program. The term "actionable" has recently been used for all IEIs with outcomes that can be demonstrably improved through early specialized intervention. OBJECTIVE: To evaluate the results of the expanded NBS strategy for IEIs in Tuscany Region (Italy), based on T-cell receptor excision circle, kappa recombining excision circle, and tandem mass-based assays. METHODS: This is a retrospective study collecting data from all infants born in Tuscany from October 10, 2018, to October 10, 2022. Tandem mass assay to identify adenosine deaminase and purine nucleoside phosphorylase deficiency, together with T-cell receptor excision circle and kappa recombining excision circle molecular analysis, was conducted on dried blood spot from the newborns' Guthrie Cards. A new dried blood spot and evaluation by an immunologist were carried out when the results of the first test were outside the diagnostic cutoffs. RESULTS: A total of 94,319 newborns were evaluated. Referral rates for T-cell recombining excision circles (0.031%) and kappa recombining excision circles (0.074%) in this study are in line with the data available in literature. The results from the expanded NBS strategy revealed an incidence rate of 1 per 9431 affected newborns. CONCLUSIONS: This work represents the first description of a sustainable and real-life-based expanded NBS program for IEIs with a high diagnostic incidence facilitating prompt management of identified patients.

Severe A(H1N1)pdm09 influenza acute encephalopathy outbreak in children in Tuscany, Italy, December 2023 to January 2024.

A severe outbreak of influenza A(H1N1pdm09) infection in seven children (median age: 52 months) occurred between December 2023 and January 2024 in Tuscany, Italy. Clinical presentation ranged from milder encephalopathy to acute necrotizing encephalopathy (ANE) with coma and multiorgan failure; one child died. This report raises awareness for clinicians to identify and treat early acute encephalopathy caused by H1N1 influenza and serves as a reminder of severe presentations of influenza in young children and the importance of vaccination.

HLH as an additional warning sign of inborn errors of immunity beyond familial-HLH in children: a systematic review.

Background: Hemophagocytic Lymphohistiocytosis (HLH) is a rare and life-threatening condition characterized by a severe impairment of the immune homeostasis. While Familial-HLH (FHL) is a known cause, the involvement of other Inborn Errors of Immunity (IEI) in pediatric-HLH remains understudied. Objective: This systematic review aimed to assess the clinical features, triggers, laboratory data, treatment, and outcomes of pediatric HLH patients with IEI other than FHL (IEInotFHL), emphasizing the importance of accurate identification and management. Methods: A systematic search for studies meeting inclusion criteria was conducted in PubMed, EMBASE, MEDLINE, and Cochrane Central. Quality assessment was performed through JBI criteria. Results: A comprehensive search yielded 108 records meeting inclusion criteria, involving 178 patients. We identified 46 different IEI according to IUIS 2022 Classification. Combined immunodeficiencies, immune dysregulation disorders, and phagocyte defects were the IEI most frequently associated with HLH. In 75% of cases, HLH preceded the IEI diagnosis, often with an unrecognized history of severe infections. Triggers reflected the specific infection susceptibilities within IEI groups. Liver and central nervous system involvement were less common than in FHL cases. Treatment approaches and outcomes varied, with limited long-term follow-up data, limiting the assessment of therapeutic efficacy across IEI groups. Conclusion: A comprehensive evaluation encompassing immunological, infectious, and genetic aspects is essential in pediatric-HLH. Relying solely on FHL or EBV susceptibility disorders tests is insufficient, as diverse other IEI can contribute to HLH. Early recognition of HLH as a potential warning sign can guide timely diagnostic investigations and facilitate tailored therapeutic interventions for improved outcomes. Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=371425, PROSPERO, CRD42022371425.

Disrupted Seasonality of Respiratory Viruses: Retrospective Analysis of Pediatric Hospitalizations in Italy from 2019 to 2023.

This multicenter study in Italian hospitals highlights the epidemiologic disruptions in the circulation of the 5 main respiratory viruses from 2019 to 2023. Our data reveal a resurgence of respiratory syncytial virus and influenza during the 2022-2023 winter season, with an earlier peak in cases for both viruses, emphasizing the importance of timely monitoring.

Similarities and differences between myocarditis following COVID-19 mRNA vaccine and multiple inflammatory syndrome with cardiac involvement in children.

Despite the multiple benefits of vaccination, cardiac adverse Events Following COVID-19 Immunization (c-AEFI) have been reported. These events as well as the severe cardiac involvement reported in Multisystem inflammatory syndrome in children (MIS-C) appear more frequent in young adult males. Herein, we firstly report on the inflammatory profiles of patients experiencing c-AEFI in comparison with age, pubertal age and gender matched MIS-C with cardiac involvement. Proteins related to systemic inflammation were found higher in MIS-C compared to c-AEFI, whereas a higher level in proteins related to myocardial injury was found in c-AEFI. In addition, higher levels of DHEAS, DHEA, and cortisone were found in c-AEFI which persisted at follow-up. No anti-heart muscle and anti-endothelial cell antibodies have been detected. Overall current comparative data showed a distinct inflammatory and androgens profile in c-AEFI patients which results to be well restricted on heart and to persist months after the acute event.

Reshaping Our Knowledge: Advancements in Understanding the Immune Response to Human Respiratory Syncytial Virus.

Human respiratory syncytial virus (hRSV) is a significant cause of respiratory tract infections, particularly in young children and older adults. In this review, we aimed to comprehensively summarize what is known about the immune response to hRSV infection. We described the innate and adaptive immune components involved, including the recognition of RSV, the inflammatory response, the role of natural killer (NK) cells, antigen presentation, T cell response, and antibody production. Understanding the complex immune response to hRSV infection is crucial for developing effective interventions against this significant respiratory pathogen. Further investigations into the immune memory generated by hRSV infection and the development of strategies to enhance immune responses may hold promise for the prevention and management of hRSV-associated diseases.

Four-Component Recombinant Protein-Based Vaccine Effectiveness Against Serogroup B Meningococcal Disease in Italy.

Importance: Population-based data on the 4-component recombinant protein-based (4CMenB) vaccine effectiveness and reduction in incidence rate ratios (IRRs) are continuously needed to assess vaccine performance in the prevention of serogroup B invasive meningococcal disease (IMD). Objective: To assess the effectiveness and reduction in IRRs associated with the 4CMenB vaccine in the pediatric population in 6 regions in Italy. Design, Setting, and Participants: This retrospective cohort screening study and case-control study included data from children aged younger than 6 years in 6 highly populated Italian regions from January 1, 2006, to January 1, 2020. Participants included children younger than 6 years diagnosed with serogroup B IMD without predisposing factors. Data were collected from regional surveillance and vaccination registries and were analyzed from September 2021 to January 2022. Exposures: Routine 4CMenB vaccination, per regional vaccination programs. Main Outcomes and Measures: The main outcome was the effectiveness of the 4CMenB vaccine in the prevention of serogroup B IMD in the population of children aged younger than 6 years in 6 Italian regions. The percentages of vaccine effectiveness (VE) were obtained through the concomitant use of a screening method and a case-control study. Secondary outcomes were the comparison of effectiveness results obtained using the 2 different computational methods, the description of serogroup B IMD incidence rates, and reduction in IRRs before and after 4CMenB introduction, as a proxy for vaccine impact. Results: The cohort screening study included a resident population of 587 561 children younger than 6 years in 3 regions with similar surveillance protocols, and the matched-case controls study assessed a resident population of 1 080 620 children younger than 6 years in 6 regions. Analyses found that 4CMenB VE in fully immunized children was 94.9% (95% CI, 83.1%-98.4%) using the screening method and 91.7% (95% CI, 24.4%-98.6%) using the case-control method. Overall reduction in IRR was 50%, reaching 70% in regions with early-start vaccination schedules. The case-control method involving 6 highly-populated Italian regions included 26 cases and 52 controls and found an estimated VE of 92.4% (95% CI, 67.6%-97.9%) in children old enough for the first vaccine dose and 95.6% (95% CI, 71.7%-99.1%) in fully immunized children. VE was more than 90% for partially immunized children. Even in regions where the first dose was administered at age 2 months, almost 20% of unvaccinated cases were among infants too young to receive the first 4CMenB dose. Conclusions and Relevance: This screening cohort study and matched case-controls study found high effectiveness of 4CMenB vaccination and greater reduction in IRR for early-start vaccination schedules in preventing invasive serogroup B meningococcal disease. The high proportion of children too young to be vaccinated among unvaccinated cases suggests that starting the vaccination even earlier may prevent more cases. Screening and case-control methods provided similar estimates of VE: either method may be used in different study settings, but concomitant use can provide more robust estimates.

Risk of thyroid neoplasms in patients with 22q11.2 deletion and DiGeorge-like syndromes: an insight for follow-up.

Introduction: The chromosome 22q11.2 deletion syndrome comprises phenotypically similar diseases characterized by abnormal development of the third and fourth branchial arches, resulting in variable combinations of congenital heart defects, dysmorphisms, hypocalcemia, palatal dysfunction, developmental or neuropsychiatric disorders, and impairment of the immune system due to thymic dysfunction. Other genetic syndromes, often called DiGeorge-like, share clinical and immunological features with 22q11.2 deletion syndrome. This syndrome has been rarely associated with malignancies, mainly hematological but also hepatic, renal, and cerebral. Rarely, malignancies in the head and neck region have been described, although no aggregate of data on the development of thyroid neoplasms in patients with this clinical phenotype has been conducted so far. Materials and methods: To characterize this possible association, a multicenter survey was made. Thus, we present a case series of five pediatric patients with 22q11.2 deletion syndrome or DiGeorge-like syndrome who were occasionally found with confirmed or highly suspected neoplasms of the thyroid gland during their follow-up. In three cases, malignancies were histologically confirmed, but their outcome was good due to an early recognition of suspicious nodules and precocious surgery. Conclusions: This study underlines for clinicians the higher risk of neoplasms in the head and neck district for patients affected by these syndromes. It also emphasizes the importance of a prolonged clinical and ultrasound follow-up for patients with this clinical and immunological phenotype.

Immunogenicity and safety of a quadrivalent meningococcal tetanus toxoid-conjugate vaccine (MenACYW-TT): A review of the evidence and expert opinion.

INTRODUCTION: Serogroups A, B, C, W, X, and Y of Neisseria meningitidis are responsible for almost all cases of invasive meningococcal disease. In Italy, vaccination against serogroup B is recommended at 3-13 months, C at 13-15 months, and A, C, Y and W in adolescents (12-18 years). Four quadrivalent meningococcal conjugate vaccines are available. This review describes the available data on a quadrivalent meningococcal tetanus toxoid-conjugate vaccine (MenACYW-TT; MenQuadfi®; Sanofi). AREAS COVERED: We identified articles on quadrivalent meningococcal conjugate vaccines indexed on PubMed since 2000. Of the 524 studies identified, 10 human studies investigating the immunogenicity and safety of MenACYW-TT in toddlers, children aged 2-9 years, and individuals 10-55 or ≥56 years are described in detail. EXPERT OPINION: In Italy, pediatric and public health groups recommend amending the current vaccination schedule to include a booster dose between 6 and 9 years and quadrivalent vaccine in young adults (≥19 years), targeting waning protection after childhood vaccination and the age cohort with the highest carrier prevalence (adolescents and young adults). MenACYW-TT is a suitable meningococcal vaccine for current and pending recommendations based on high seroprotection rates and a low incidence of adverse events in these age groups. Moreover, it does not require reconstitution.

CD38high/HLA-DR+ CD8+ T cells as potential biomarker of hemophagocytic lymphohistiocytosis secondary to visceral Leishmania infection.

Leishmaniasis is a cause of infection associated with hemophagocytic lymphohistiocytosis (HLH). The measurement of the CD8+ CD38high/HLA-DR+ T cells in children presenting with acute onset of shock and multisystem organ failure represents an important parameter to distinguish HLH from sepsis or healthy control. CONCLUSION: We report a case series of 4 Italian children suffering from HLH secondary to visceral Leishmaniasis in which the lymphocyte subset assay suggests a potential role of CD38high/HLA-DR+ CD8+ T cells as HLH diagnostic biomarkers. WHAT IS KNOWN: • Visceral Leishmaniasis is a well-known cause of infection associated with hemophagocytic lymphohistiocytosis (HLH). • The measurement of the CD8+ CD38high/HLA-DR+ T cells in children presenting with acute onset of shock and multisystem organ failure represents an important diagnostically useful parameter to readily distinguish HLH from sepsis or healthy controls. WHAT IS NEW: • We report a case series of 4 Italian children suffering from HLH secondary to visceral Leishmaniasis in which the lymphocyte subset assay suggests a potential role of CD38high/HLA-DR+ CD8+ T cells as HLH diagnostic biomarker. • The flow cytometry assay, performed at the disease onset before starting treatment, revealed a mean percentage value of CD38 cells of 36.95% among CD8+ T cells.