T Cell Responsiveness Through the Ages: Functional Diversity of Age-Dependent Antiviral Responses
An organism’s age impacts its susceptibility to disease, which varies according to the type of insult or causal pathogen. Much work remains to delineate these complexities, especially within younger individuals. Indeed, pediatric disease-driven immunity is less characterized than adult and aging populations due to two main factors: 1) descriptions through multiple stages of development are required, as the immune system undergoes massive changes from gestation through the end of adolescence, and 2) the complex nature of pediatric research decreases the availability of robust and comprehensive studies. Importantly, studying the immune system in relation to age requires a foundational knowledge within adult individuals to adequately assess the unique characteristics of the developing and aged systems. This body of work contributes to the field of age-dependent immunity via the study of repair-associated T cell subsets in pediatric acute respiratory distress syndrome (pARDS), γδ T cells in murine cytomegalovirus (MCMV), and multiple immune mediators and cell populations in adult severe influenza infection. Single-cell RNA sequencing of tracheal aspirate cells from pediatric subjects experiencing acute respiratory failure (ARF) showed that distinct T cell subsets within the lower respiratory tract exhibited transcriptional similarity, termed functional redundancy. This similarity was repair-associated, and a defining gene of the transcriptional profile was amphiregulin (AREG). When quantified, T cells from subjects with a viral lower respiratory tract infection (LRTI) that did not progress to moderate or severe pARDS had significantly elevated repair scores. This was reflected within tissue resident memory (TRM) CD8 T cells, activated regulatory CD4 T cells (Tregs), and activated AREG+ γδ T cells. The repair profile was then applied across publicly available datasets spanning ages, tissue types, etiologies, and severities, and functional redundancy was only observed within the same three subsets of tracheal aspirate T cells from healthy pediatric subjects. Additional validation confirmed that nasal wash supernatant proteins from the repair profile were inversely correlated with age. Collectively, these findings indicated that T cells within the respiratory tract exhibited functional redundancy linked to tissue repair in an age-dependent manner, and that this redundancy was associated with decreased disease severity. Results from mouse models of MCMV infection demonstrated that the functionality of γδ T cells is shaped by infection in an age-specific manner. γδ T cells from neonates infected with MCMV underwent a shift in cytokine production that was absent in acutely infected adult, aged, and geriatric mice. Neonatal infection also affected the γδ T cell receptor (TCR) repertoire by modulating the hierarchy of segment usage. Single-cell RNA sequencing with paired TCR repertoire data from the lungs showed that both age and MCMV infection impacted γδ T cells in a manner determined by age of viral exposure, viral state, and age of the mouse at endpoint characterization. These data highlight age-associated functionality of γδ T cells in MCMV infection, and the role that age of exposure plays in shaping γδ T cell immunity. Lastly, a cohort of oseltamivir-treated adults with severe influenza infection were utilized to address 3 questions: 1) What is the relationship between patient risk and severity scores throughout severe influenza infection? 2) What immunological features underlay severe influenza infection? 3) What immune biomarkers are predictive of infection severity and clinical outcome? First, assessment of the relationship between risk and severity scores showed increased correlation between metrics that incorporated supplemental oxygen usage, as well as those which were less subjective in nature. No correlations were observed for intake risk metrics or subjective severity scoring. Second, a decrease in protection-associated cytokines and innate immune mediators was observed over the course of severe infection across all individuals. Additionally, subjects with heightened severity exhibited decreased upper respiratory and peripheral pro-inflammatory and pleiotropic cytokines at study day 0, decreased T cells spanning naive and memory phenotypes at study days 0, 3, and 28, and decreased peripheral eotaxin at study day 28. Third, peripheral myeloid analytes were positively associated with severity based on intake vitals, while cytotoxic natural killer T (NKT) cells were negatively associated. Multiple circulating and upper respiratory cytokines were predictive of peak infection severity, as was the frequency of circulating eosinophils. For correlative analyses, age was included in all linear regression modeling, since the study included both adult and elderly individuals. In conclusion, these data established the presence of functionally redundant pediatric T cells in the airway, identified age-associated features of γδ T cells in MCMV-infected lungs, and laid the foundation for studies of severe influenza infection in antiviral-treated individuals across different ages. The unique functions of pediatric T cells in this body of work widen the scope of future age-associated immune studies, which will impact study design, interpretation, and subsequent therapeutic development.
Age;Influenza;MCMV;pARDS;T cell;γδ T cell, Medicine and Health Sciences
University of Tennessee Health Science Center
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