Background: The main source of vitamin D is skin synthesis, which depends on sunlight exposure. During the pandemic, COVID-19 children were obliged to home confinement, which potentially limiting sunlight exposure. The aim of this study was to evaluate whether home confinement led to decreased vitamin D serum levels in children in Warsaw, Poland. Methods: The study included 1472 children who were divided into two groups, based on the date of 25(OH)D level blood sampling: before and during the pandemic. Children under 1 year of age (infants) were analysed separately. Results: A statistically significant decrease in the average level of vitamin D was observed between groups of children over 1 year of age (35 ng/mL ± 18 vs. 31 ng/mL ± 14). In infants from both groups, the mean vitamin D levels were within the normal range (Group 1 inf 54 ng/mL ± 21 vs. Group 2 inf 47 ng/mL ± 15). The characteristic seasonal variability was observed before the pandemic, with maximal vitamin D levels in summer (40 ng/mL ± 17) and minimal levels in winter (30 ng/mL ± 14). During the pandemic, no seasonal variability was observed (summer 30 ng/mL ± 11 vs. winter 30 ng/mL ± 19). Conclusions: The COVID-19 pandemic restrictions led to a significant decrease in vitamin D serum levels in children.

Vitamin D, in addition to its superior role as a factor regulating calcium-phosphate metabolism, shows wide effects in other processes in the human body, including key functions of the immune system. This is due to the presence of vitamin D receptors in most cells of the human body. In our study, we aimed to assess whether there is a correlation between vitamin D content and the clinical course of allergic diseases as well as establish their immunological parameters in children. We found that vitamin D deficiency was significantly more frequent in the group of children with an allergic disease than in the control group (p = 0.007). Statistically significant higher vitamin D concentrations in blood were observed in the group of children with a mild course of the disease compared to children with a severe clinical course (p = 0.03). In the group of children with vitamin D deficiency, statistically significant lower percentages of NKT lymphocytes and T-regulatory lymphocytes were detected compared to the group of children without deficiency (respectively, p = 0.02 and p = 0.05), which highlights a potential weakness of the immune system in these patients. Furthermore, statistically higher levels of interleukin-22 were observed in the group of children with vitamin D deficiency (p = 0.01), suggesting a proinflammatory alert state. In conclusion, these results confirm the positive relationship between the optimal content of vitamin D and the lesser severity of allergic diseases in children, establishing weak points in the immune system caused by vitamin D deficiency in children.

Asthma is one of the most common chronic diseases. Epidemiological studies show that asthma will develop among around 40% of children under six years old with symptoms of bronchial obstruction.Diagnosis of asthma is complicated, especially in the paediatric population. As a result, a lot of research is being carried out to establish the pathophysiology and to find new biomarkers of this disease. Progranulin (PGRN) is a recently discovered growth factor with many biological functions. PGRN has anti-inflammatory properties because it inhibits neutrophil degranulation and blocks tumor necrosis factor α (TNF-α) transmission. The underlying mechanisms are still being researched, but TNF-α is considered to be a cytokine responsible for neutrophilic inflammation in the airways and bronchial hyperresponsiveness. Therefore, PGRN, by lowering TNF-α concentration and stimulating regulatory T-cell (Treg) prolifera­tion, relieves symptoms of bronchial inflammatory diseases. This article attempts to verify the current knowledge about basic pathophysiological mechanisms in asthma. We also summarise the most recent research advances in the role of PGRN in the respiratory system.

Absence of the inferior vena cava is a rare vascular anomaly, which usually remains asymptomatic in childhood. It is recognized as the risk factor for deep venous thrombosis, since the collateral circulation does not provide adequate drainage of the lower limbs. Mycoplasma pneumoniae is a common cause of community-acquired pneumonia in school-aged children and adolescents. Mycoplasma pneumoniae infection might be associated with deep venous thrombosis but its pathophysiology remains unknown. According to previous reports, deep venous thrombosis due to Mycoplasma pneumoniae infection is associated with positive serum anticardiolipin antibodies. To our knowledge, we describe the first case of deep venous thrombosis associated with Mycoplasma pneumoniae serum antibodies indicating early stage of infection with negative anticardiolipin serum antibodies in adolescent with absence of inferior vena cava. 14-year old boy was admitted to the pediatric unit few days after the appendectomy complaining with pain of the left hip that caused him unable to walk. The pain was accompanied with subfebrile temperature. After clinical examination and additional tests, the boy was diagnosed with a deep venous thrombosis. Computed tomography revealed absence of the vena cava inferior distally to the hepatic veins and varices of the collateral circulation in the pelvis. Anticardiolipin IgM and IgG antibodies and antinuclear antibodies were not detected. Additionally, the Mycoplasma pneumoniae antibodies in classes IgM, IgA and IgG were detected in serum as another risk factor of thrombosis. After the initial treatment with low-molecular-weight heparin in combination with clarithromycin the clinical condition of the patient improved. The patient became a candidate for life-long anticoagulation therapy. In this case Mycoplasma pneumoniae antibodies were associated with deep venous thrombosis in child with congenital absence of inferior vena cava. Uncommonly for deep venous thrombosis due to Mycoplasma pneumoniae infection, anticardiolipin antibodies were not detected in serum. It is important to remember in clinical practice that Mycoplasma pneumoniae affects coagulability and may trigger thrombosis, especially in the presence of other risk factors. The pathophysiology of this process remains unknown.

Due to the increased incidence of allergic diseases and emerging effects of unsatisfactory control of asthma, new mechanisms for supervising the immune system should be searched. The aim of the study was to analyze the percentage of CD3, CD4, CD8, CD19, CD16/56, NKT, CD3 anti-HLADR3 and Foxp3 regulatory lymphocytes in patients with asthma. Additionally the correlation between immune parameters, severity of asthma and serum concentration of vitamin D was performed. 25 children diagnosed with asthma were enrolled. Disease severity was assessed with the Asthma Control Test (ACT) and spirometry. The control group consisted of 15 healthy children. Venous blood from each patient was collected on EDTA or on “clott”. Phenotypes of lymphocytes were evaluated by flow cytometry. Vitamin D concentration was assessed by chemiluminescent immunoassay (CLIA) technology. There was a significant decrease in the percentage of T regulatory cells (p < 0.006) in children with asthma compared to the control group. There were no significant differences in the other investigated immunological parameters. In addition, in asthma group statistically significant decreased of vitamin D concentration (p < 0.04) was observed. There were also no significant correlations between vitamin D3 concentration and the course of asthma or percentage of regulatory cells. The results confirmed the role of regulatory T cells in the pathogenesis of asthma. Effects of vitamin D on the severity of the disease has not been proven.