Kirsten I. M. Looman

Objective: The pathogenesis of attention‐deficit/hyperactivity disorder (ADHD) is currently unclear. We hypothesized that chronic immune activation, as indexed by T and B cells, plays a role in the pathophysiology of attention problems. Therefore, we examined T and B cell subsets in a general pediatric population with information on attention problems.Methods: We included 756 10‐year‐old children from the Generation R population‐based cohort. Eleven‐color flow cytometry was performed on peripheral blood samples to determine T and B cell subsets. The Child Behavior Checklist rated by parents was used to measure attention problems. Data were analyzed using linear regression analyses, adjusting for maternal and child covariates and co‐occurring childhood psychopathology.Results: For T helper 1 (Th1) cells, one standard deviation (SD) increase was associated with 5.3% (95%CI 0.3; 10.5) higher attention problem scores. Furthermore, 1SD increase in CD8⁺ T cells was associated with 7.5% (95%CI 2.4; 12.7) higher attention problem scores. Within total CD8⁺ T cells, 1SD increase in naive or central memory cells was associated with 6.9% (95%CI 2.0; 12.1) and 6.4% (95%CI 1.5; 11.6) higher attention problem scores, respectively. No associations between Th2, Treg or B memory cells and attention problem scores were observed.Conclusion: Higher Th1 and cytotoxic T cell numbers are associated with higher attention problem scores independent of co‐occurring psychopathology. This might indicate a possible role of a pro‐inflammatory immune profile in childhood attention problems.

Context Adult obesity is associated with chronic low-grade inflammation and may give rise to future chronic disease. However, it is unclear whether adiposity-related inflammation is already apparent in childhood. Objective To study associations between child adiposity measures with circulating monocytes and naive and memory subsets in CD4, CD8, and γδ T cell lineages. Methods Ten-year-old children (n = 890) from the Generation R Cohort underwent dual-energy x-ray absorptiometry and magnetic resonance imaging for body composition (body mass index [BMI], fat mass index [FMI], android-to-gynoid fat mass ratio, visceral fat index, liver fat fraction). Blood samples were taken for detailed immunophenotyping of leukocytes by 11-color flow cytometry. Results Several statistically significant associations were observed. A 1-SD increase in total FMI was associated with +8.4% (95% CI 2.0, 15.2) Vδ2⁺Vγ9⁺ and +7.4% (95% CI 2.4, 12.5) CD8⁺_TEMRO cell numbers. A 1-SD increase in visceral fat index was associated with +10.7% (95% CI 3.3, 18.7) Vδ2⁺Vγ9⁺ and +8.3% (95% CI 2.6, 14.4) CD8⁺_TEMRO cell numbers. Higher android-to-gynoid fat mass ratio was only associated with higher Vδ2⁺Vγ9⁺ T cells. Liver fat was associated with higher CD8⁺_TEMRO cells but not with Vδ2⁺Vγ9⁺ T cells. Only liver fat was associated with lower Th17 cell numbers: a 1-SD increase was associated with −8.9% (95% CI −13.7, −3.7) Th17 cells. No associations for total CD8⁺, CD4⁺ T cells, or monocytes were observed. BMI was not associated with immune cells. Conclusion Higher Vδ2⁺Vγ9⁺ and CD8⁺_TEMRO cell numbers in children with higher visceral fat index could reflect presence of adiposity-related inflammation in children with adiposity of a general population.

Background: An association has been reported between early life Staphylococcus aureus nasal carriage and higher risk of childhood eczema, but it is unclear whether this relationship is causal and associations with other bacterial species are unclear.Objective: To examine the associations of early life nasal and nasopharyngeal bacterial carriage with eczema phenotypes, and the direction of any associations identified.Methods: Among 996 subjects of a population‐based prospective cohort study, nasal swabs for Staphylococcus  aureus, and nasopharyngeal swabs for Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae were collected and cultured from age 6 weeks to 6 years. Never, early, mid‐, late transient and persistent eczema phenotypes were identified from parental‐reported physician‐diagnosed eczema from age 6 months until 10 years. Multinomial regression models and cross‐lagged models were applied.Results: Staphylococcus aureus nasal carriage at 6 months was associated with an increased risk of early transient and persistent eczema (OR (95% CI): 2.69 (1.34, 5.39) and 4.17 (1.12, 15.51)). The associations between Staphylococcus aureus nasal carriage and eczema were mostly cross‐sectional, and not longitudinal. No associations of Staphylococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenza nasopharyngeal bacterial carriage with eczema and eczema phenotypes were observed (OR range (95% CI): 0.71 (0.35, 1.44) to 1.77 (0.84, 3.73)).Conclusions: Early life Staphylococcus aureus nasal carriage, but not Staphylococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenza nasopharyngeal carriage, was associated with early transient and persistent eczema. Staphylococcus aureus nasal carriage and eczema were mostly cross‐sectionally associated, and not longitudinally, making a causal relationship in either direction unlikely.

Background: Mutations in the filaggrin gene (FLG) affect epidermal barrier function and increase the risk of atopic dermatitis (AD). We hypothesized that FLG mutations affect immune cell composition in a general pediatric population. Therefore, we investigated whether school‐aged children with and without FLG mutations have differences in T‐ and B‐cell subsets.Methods: This study was embedded in a population‐based prospective cohort study, the Generation R Study, and included 523 children of European genetic ancestry aged 10 years. The most common FLG mutations in the European population (R501X, S1085CfsX36, R2447X, and S3247X) were genotyped. Additionally, 11‐color flow cytometry was performed on peripheral blood samples to determine helper T (Th), regulatory T (Treg), and CD27⁺ and CD27^‐ memory B cells. Subset analysis was performed in 358 non‐AD and 102 AD cases, assessed by parental questionnaires.Results: FLG mutations were observed in 8.4% of the total population and in 15.7% of the AD cases. Children with any FLG mutation had higher Th22 cell numbers compared to FLG wild‐type children in the general and non‐AD population. Children with and without FLG mutations had no difference in Th1, Th2, Th17, Treg, or memory B‐cell numbers. Furthermore, in children with AD, FLG mutation carriership was not associated with differences in T‐ and B‐cell subsets.Conclusions: School‐aged children of a general population with FLG mutations have higher Th22 cell numbers, which reflects the immunological response to the skin barrier dysfunction. FLG mutations did not otherwise affect the composition of the adaptive immunity in this general pediatric population.

A previously healthy 40-year-old man was referred to our emergency department with pruritic skin lesions and dyspnoea. Laboratory investigation revealed hypereosinophilia. Further diagnostic work-up confirmed the diagnosis of idiopathic hypereosinophilic syndrome (iHES), a rare myeloproliferative disease with a heterogeneous clinical presentation. We describe a unique case with cardiac, pulmonary, hepatic and cutaneous involvement at time of presentation. This case accentuates the importance of an extensive multidisciplinary diagnostic work-up, since iHES is a condition with potential rapid progressive multiorgan failure which requires prompt analysis and treatment. In addition, this case emphasises the importance of being aware of tunnel vision, especially during the COVID-19 pandemic, which might give rise to an increased risk of missing rare diagnoses. Our patient was treated with prednisolone, after which both his clinical condition and eosinophil concentrations markedly improved.

Background: Mutations in the filaggrin gene (FLG) affect epidermal barrier function and increase the risk of atopic dermatitis (AD). We hypothesized that FLG mutations affect immune cell composition in a general pediatric population. Therefore, we investigated if school-aged children with and without FLG mutations have differences in immune cell numbers. Methods: This study was embedded in a population-based prospective cohort study, the Generation R Study, and included 523 children of European genetic ancestry aged 10 years. The most common FLG mutations in the European population (R501X, S1085CfsX36, R2447X and S3247X) were genotyped. Additionally, 11-color flow cytometry was performed on peripheral blood samples to determine helper T (Th), regulatory T (Treg) and CD27+ and CD27- memory B cells. Sensitivity analysis was performed in 102 AD cases, assessed by parental questionnaires. Results: FLG mutations were observed in 8.4% of the total population and in 15.7% of the AD cases. Children with any FLG mutation had higher Th22 cell numbers compared to FLG wild-type children. Children with and without FLG mutations had no difference in Th1, Th2, Th17, Treg or memory B cell numbers. Furthermore, in children with AD, FLG mutation carriership was not associated with differences in T- and B-cells or their subsets. Conclusions: School-aged children with FLG mutations have higher Th22 cell, which might suggest an immunological defense mechanism to an altered skin barrier function. No associations between Th or Treg cells and FLG mutations suggests that FLG mutations do not otherwise affect immune composition in a general pediatric population.

Background: Airway bacterial carriage might play a role in respiratory disease. We hypothesize that nasal carriage with Staphylococcus aureus or nasopharyngeal carriage with Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae predisposes individuals to adverse respiratory health.Objective: To examine the association of early‐life airway bacterial carriage with respiratory tract infections and vice versa, and of early‐life airway bacterial carriage with wheezing, lung function, and asthma in later childhood.Methods: We collected upper airway swabs for bacterial culturing for S aureus, H influenzae, M catarrhalis, and H influenzae at six timepoints between the ages of 6 weeks and 6 years among 945 children participating in a population‐based prospective cohort study. Information on respiratory tract infections and wheezing until age 6 years, and asthma at age 10 years was obtained by questionnaires. Lung function at age 10 years was measured by spirometry. We tested possible bidirectional associations between airway bacterial carriage and respiratory tract infections by cross‐lagged models, and associations of repeatedly measured airway bacterial carriage with wheezing, lung function, and asthma by generalized estimating equations models and regression models.Results: Cross‐lagged modeling showed that early‐life airway bacterial carriage was not consistently associated with upper and lower respiratory tract infections or vice versa. Nasopharyngeal carriage with any bacteria in infancy was associated with an increased risk of wheezing (OR [95% CI]: 1.66 [1.31, 2.10]). Airway bacterial carriage was not consistently associated with school‐age lung function or asthma.Conclusion: Nasopharyngeal carriage with any bacteria is associated with wheezing, but not respiratory tract infections, asthma, or lung function.

Background: New insights into immune cells could contribute to treatment and monitoring of atopic disease. Because nongenetic factors shape the human immune system, we here studied these immune cells in a large cohort with atopic children with adjustment for prenatal and postnatal confounders.Methods: Information on atopic dermatitis, inhalant‐ and food‐allergic sensitization, asthma lung function scores was obtained from 855 10‐year‐old children within the Generation R cohort. 11‐color flow cytometry was performed to determine CD27⁺ and CD27⁻IgG⁺, IgE⁺ and IgA⁺ memory B cells, Th1, Th2, Th17, and Treg‐memory cells from venous blood. Associations between any atopic disease, the individual atopic diseases, and immune cell numbers were determined.Results: Children with any atopic disease had higher Th2, Treg, Treg‐memory, and CD27⁺IgA⁺ memory B‐cell numbers compared to children without atopic disease. When studying the individual diseases compared to children without the individual diseases, children with atopic dermatitis, inhalant‐, and food‐allergic sensitization had higher memory Treg cell numbers 12.3% (95% CI 4.2; 21.0), (11.1% (95% CI 3.0; 19.8), (23.7% (95% CI 7.9; 41.8), respectively. Children with food‐allergic sensitization had higher total B and CD27⁺IgA⁺ memory B‐cell numbers (15.2% [95% CI 3.2; 28.7], 22.5% [95% CI 3.9; 44.3], respectively). No associations were observed between asthma and B‐ or T‐cell numbers.Conclusion: Children with any atopic disease and children with inhalant‐ and food‐allergic sensitization or atopic dermatitis had higher circulating memory Treg cells, but not higher IgE⁺B‐cell numbers. The associations of higher Treg and CD27⁺IgA⁺ B‐cell numbers in children with food‐allergic sensitization are suggestive of TGF‐β‐mediated compensation for chronic inflammation.

Background: Previous studies have demonstrated that vitamin D affects T‐cell function and maturation via the vitamin D receptor. However, no studies in children have been performed on this topic. Because most of the T‐cell memory is formed in the first 5 years of life, we aimed to determine the association between serum 25‐hydroxyvitamin D (25(OH)D) levels and numbers of circulatory naive, central memory (Tcm), and effector memory (Tem) T lymphocytes in a large population of healthy children.Methods: Among 3189 children participating in a population‐based prospective cohort, we measured 25(OH)D levels and performed detailed immunophenotyping of naive and memory T lymphocytes at a median age of 6.0 years (95% range 5.7‐7.9). Detailed lymphocyte subsets were available in 986 children. Multivariable linear regression analyses were performed to determine the association between 25(OH)D and the maturation of T lymphocytes in children adjusted for cord blood 25(OH)D levels, herpes seropositivity, sociodemographic and lifestyle confounders. Furthermore, multivariable logistic regression analyses were performed to determine associations between 25(OH)D and childhood infections.Results: Higher 25(OH)D levels were associated with higher numbers of Tem lymphocytes. Every 10 nmol/L higher 25(OH)D was associated with 2.20% (95% CI 0.54‐3.89; P=.009) higher CD4TemRA, 1.50% (95% CI 0.38‐2.62; P=.008) higher CD4TemRO, and 1.82% (95% CI 0.11‐3.56; P=.037) higher CD8TemRA cell numbers. Generally, stronger associations were observed among boys. 25(OH)D levels were not significantly associated with naive, Tcm cell numbers, herpes seropositivity, or URTIs.Conclusions: Our results suggest that vitamin D enhances cellular immunity in young children.