Thymus activity measured by T-cell receptor excision circles in patients with different severities of respiratory syncytial virus infection

Changes in Thymic Size and Immunity Are Associated with Bronchopulmonary Dysplasia

OBJECTIVE

Preterm infants with bronchopulmonary dysplasia (BPD) are at increased risk for dysfunctional immune responses in the postnatal period. This study aimed to verify the hypothesis that thymic function is altered in infants with BPD and changes in the expression of thymic function-related genes affect thymic development.

STUDY DESIGN

Included in the study were infants who had a gestational age ≤32 weeks and survived to a postmenstrual age of ≥36 weeks. The clinical features and thymic size were comparatively studied between infants with and without BPD. Thymic function and the expression of thymic function-related genes were determined in BPD infants at birth, week 2, and 4 of life. The thymic size was ultrasonographically assessed in terms of the thymic index (TI) and thymic weight index (TWI). T-cell receptor excision circles (TRECs) and gene expression were quantitatively determined by real-time quantitative reverse transcription polymerase chain reaction.

RESULTS

Compared to non-BPD infants, their BPD counterparts had a shorter GA, lower birth weight, lower Apgar scores at birth, and were more likely to be of the male gender. BPD infants had an elevated incidence of respiratory distress syndrome and sepsis. TI was 1.73 ± 0.68 versus 2.87 ± 0.70 cm3 and TWI was 1.38 ± 0.45 versus 1.72 ± 0.28 cm3/kg in the BPD group versus the non-BPD group (p < 0.05). In BPD infants, no significant changes were observed in thymic size, lymphocyte counts, and TREC copy numbers at the first 2 weeks (p > 0.05), but they all exhibited a significant increase at week 4 (p < 0.05). BPD infants presented a trend toward increased expression of transforming growth factor-β1 and decreased expression of forkhead box protein 3 (Foxp3) from birth to week 4 (p < 0.05). Nonetheless, no significant difference was found in IL-2 or IL-7 expression at all time points (p > 0.05).

CONCLUSION

For preterm infants with BPD, reduced thymic size at birth might be associated with impaired thymic function. Thymic function was developmentally regulated in the BPD process.

KEY POINTS

· For preterm infants with BPD, reduced thymic size at birth might be associated with impaired thymic.. · BPD infants had an elevated incidence of respiratory distress syndrome and sepsis.. · Thymic function was developmentally regulated in the BPD process..

Pneumonia and Related Conditions in Critically Ill Patients—Insights from Basic and Experimental Studies

Pneumonia is an acute infectious disease with high morbidity and mortality rates. Pneumonia’s development, severity and outcome depend on age, comorbidities and the host immune response. In this study, we combined theoretical and experimental investigations to characterize pneumonia and its comorbidities as well as to assess the host immune response measured by TREC/KREC levels in patients with pneumonia. The theoretical study was carried out using the Columbia Open Health Data (COHD) resource, which provides access to clinical concept prevalence and co-occurrence from electronic health records. The experimental study included TREC/KREC assays in young adults (18–40 years) with community-acquired (CAP) (n = 164) or nosocomial (NP) (n = 99) pneumonia and healthy controls (n = 170). Co-occurring rates between pneumonia, sepsis, acute respiratory distress syndrome (ARDS) and some other related conditions common in intensive care units were the top among 4170, 3382 and 963 comorbidities in pneumonia, sepsis and ARDS, respectively. CAP patients had higher TREC levels, while NP patients had lower TREC/KREC levels compared to controls. Low TREC and KREC levels were predictive for the development of NP, ARDS, sepsis and lethal outcome (AUC_TREC in the range 0.71–0.82, AUC_KREC in the range 0.67–0.74). TREC/KREC analysis can be considered as a potential prognostic test in patients with pneumonia.

Effect of Coxsackievirus B4 Infection on the Thymus: Elucidating Its Role in the Pathogenesis of Type 1 Diabetes

The thymus gland is a primary lymphoid organ for T-cell development. Various viral infections can result in disturbance of thymic functions. Medullary thymic epithelial cells (mTECs) are important for the negative selection of self-reactive T-cells to ensure central tolerance. Insulin-like growth factor 2 (IGF2) is the dominant self-peptide of the insulin family expressed in mTECs and plays a crucial role in the intra-thymic programing of central tolerance to insulin-secreting islet β-cells. Coxsackievirus B4 (CVB4) can infect and persist in the thymus of humans and mice, thus hampering the T-cell maturation and differentiation process. The modulation of IGF2 expression and protein synthesis during a CVB4 infection has been observed in vitro and in vivo in mouse models. The effect of CVB4 infections on human and mouse fetal thymus has been studied in vitro. Moreover, following the inoculation of CVB4 in pregnant mice, the thymic function in the fetus and offspring was disturbed. A defect in the intra-thymic expression of self-peptides by mTECs may be triggered by CVB4. The effects of viral infections, especially CVB4 infection, on thymic cells and functions and their possible role in the pathogenesis of type 1 diabetes (T1D) are presented.

Insights into Thymus Development and Viral Thymic Infections

T-cell development in the thymus is a complex and highly regulated process, involving a wide variety of cells and molecules which orchestrate thymocyte maturation into either CD4⁺ or CD8⁺ single-positive (SP) T cells. Here, we briefly review the process regulating T-cell differentiation, which includes the latest advances in this field. In particular, we highlight how, starting from a pool of hematopoietic stem cells in the bone marrow, the sequential action of transcriptional factors and cytokines dictates the proliferation, restriction of lineage potential, T-cell antigen receptors (TCR) gene rearrangements, and selection events on the T-cell progenitors, ultimately leading to the generation of mature T cells. Moreover, this review discusses paradigmatic examples of viral infections affecting the thymus that, by inducing functional changes within this lymphoid gland, consequently influence the behavior of peripheral mature T-lymphocytes.