Citations

Abstract Alveolar Macrophages (AMs) are a unique population of innate immune cells that reside in the alveolar space and contribute to accommodate the ever-changing need of the lungs against the external environmental challenges. AMs derive from the fetal origins and are capable of maintaining themselves through self-renewal without the input of hematopoiesis during the adulthood. However, little is known about how aging is influencing the molecular characteristics and heterogeneity of the AMs during homeostasis. Using single-cell RNA sequencing (scRNA-seq) and Seurat clustering, we discovered AMs can be subdivided into different “subsets” with unique molecular characteristics during homeostasis. Interestingly, when we further investigate the AM population with the combined data from the young(~8w) and old(~2y) mice, the data suggested that the proliferating cell fall in the same cluster with reduced number in the old-mice group, while the poised inflammatory cells showed distinct molecular patterns between the group with different age. We hypothesize that the inflammatory and the self-renewal AM subpopulations may be maintained by distinct extracellular signals. With the progress of aging, the self-renewal ability of AMs would reduce because of the number of proliferating cells but not the change of molecular patterns. At the same time, the inflammatory population would change its characteristics with age, and potentially lead to functional change upon activation. Further validation of the AM subset identity as well as the developmental and functional interrelationship of these subsets are required. In addition, the extrinsic and intrinsic signals responsible for the maintenance of these AM subsets are to be explored.

Abstract The role of Bcl6 expression in different immune compartments in regulating anti-tumor immunity is relatively unknown. Previous studies have linked Bcl6 expression in PBMC with poor prognosis in non-small cell lung cancer. We found that high expression of Bcl6 in tumor predicts survival in gastric and ovarian cancers. Using cell type specific conditional knockouts, we were able to investigate the contribution of Bcl6 expression in different lineages in modulating immune response to subcutaneously implanted B16-ova melanoma tumors. Myeloid deficiency of Bcl6 results in decreased tumor growth and metastasis. This is accompanied by enrichment of antigen specific T cells within the tumor. These tumor infiltrating T cells show an increased expression of exhausted markers such as PD-1, Lag-3 and Tim-3. Tumor associated innate cells also upregulate PD-L1. Furthermore, the TILs display an enhanced effector profile measured by robust production of granzyme B, interferon gamma and CCL3 on ex vivo stimulation. This is accompanied by increase in poly-functional CD8 T cells. Our result suggests that Bcl6 expression in the monocyte/macrophage lineage dampens the development of effective anti-tumor immunity and augments immunosuppressive tumor microenvironment. We will elucidate the exact underlying mechanisms and evaluate the translational potential of Bcl6 inhibitors in conjunction with immune checkpoint blockade in the future.

Abstract Alveolar macrophages (AMs) are major lung tissue-resident macrophages capable of proliferating and self-renewal in situ. AMs are vital in pulmonary antimicrobial immunity and surfactant clearance. The mechanisms regulating AM compartment formation and maintenance remain to be fully elucidated currently. In this study, we have explored the roles of mitochondrial transcription factor A (TFAM)–mediated mitochondrial fitness and metabolism in regulating AM formation and function. We found that TFAM deficiency in mice resulted in significantly reduced AM numbers and impaired AM maturation in vivo. TFAM deficiency was not required for the generation of AM precursors nor the differentiation of AM precursors into AMs, but was critical for the maintenance of AM compartment. Mechanistically, TFAM deficiency diminished gene programs associated with AM proliferation and self-renewal and promoted the expression of inflammatory genes in AMs. We further showed that TFAM-mediated AM compartment impairment resulted in defective clearance of cellular debris and surfactant in the lung and increased the host susceptibility to severe influenza virus infection. Finally, we found that influenza virus infection in AMs led to impaired TFAM expression and diminished mitochondrial fitness and metabolism. Thus, our data have established the critical function of TFAM-mediated mitochondrial metabolism in AM maintenance and function.

Age-associated T RM cell malfunction supports chronic lung inflammation and tissue fibrosis after respiratory viral infection.

Neutrophils are vital for antimicrobial defense; however, their role during viral infection is less clear. Furthermore, the molecular regulation of neutrophil fate and function at the viral infected sites is largely elusive. Here we report that BCL6 deficiency in myeloid cells exhibited drastically enhanced host resistance to severe influenza A virus (IAV) infection. In contrast to the notion that BCL6 functions to suppress innate inflammation, we find that myeloid BCL6 deficiency diminished lung inflammation without affecting viral loads. Using a series of Cre-transgenic, reporter, and knockout mouse lines, we demonstrate that BCL6 deficiency in neutrophils, but not in monocytes or lung macrophages, attenuated host inflammation and morbidity following IAV infection. Mechanistically, BCL6 bound to the neutrophil gene loci involved in cellular apoptosis in cells specifically at the site of infection. As such, BCL6 disruption resulted in increased expression of apoptotic genes in neutrophils in the respiratory tract, but not in the circulation or bone marrow. Consequently, BCL6 deficiency promoted tissue neutrophil apoptosis. Partial neutrophil depletion led to diminished pulmonary inflammation and decreased host morbidity. Our results reveal a previously unappreciated role of BCL6 in modulating neutrophil apoptosis at the site of infection for the regulation of host disease development following viral infection. Furthermore, our studies indicate that tissue-specific regulation of neutrophil survival modulates host inflammation and tissue immunopathology during acute respiratory viral infection.

Respiratory viral infections, like IAV and respiratory syncytial virus (RSV) infections, impose great challenges to public health. Alveolar macrophages (AM) are lung-resident immune cells that play important roles in protecting the host against IAV and RSV infections. However, the underlying molecular mechanisms by which AM modulate host inflammation, disease development, and tissue recovery are not very well understood. Here we identify that PPAR-γ expression in AM is crucial to suppress pulmonary inflammation and diseases and to promote fast host recovery from IAV and RSV infections. Our data suggest that targeting macrophage PPAR-γ may be a promising therapeutic option in the future to suppress acute inflammation and simultaneously promote recovery from severe diseases associated with respiratory viral infections.