Timing influences the impact of aryl hydrocarbon receptor activation on the humoral immune response to respiratory viral infection.

Humoral responses to respiratory viruses, such as influenza viruses, develop over time and are central to protection from repeated infection with the same or similar viruses. Epidemiological and experimental studies have linked exposures to environmental contaminants that bind the aryl hydrocarbon receptor (AHR) with modulated antibody responses to pathogenic microorganisms and common vaccinations. Other studies have prompted investigation into the potential therapeutic applications of compounds that activate AHR. Herein, using two different AHR ligands [2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2-(1H-Indol-3-ylcarbonyl)-4-thiazolecarboxylic acid methyl ester (ITE), to modulate the duration of AHR activity, we show that the humoral response to viral infection is dependent upon the duration and timing of AHR signaling, and that different cellular elements of the response have different sensitivities. When AHR activation was initiated prior to infection with influenza A virus, there was suppression of all measured elements of the humoral response (i.e., the frequency of T follicular helper cells, germinal center B cells, plasma cells, and circulating virus-specific antibody). However, when the timing of AHR activation was adjusted to either early (days -1 to +5 relative to infection) or later (days +5 onwards), then AHR activation affected different aspects of the overall humoral response. These findings highlight the importance of considering the timing of AHR activation in relation to triggering an immune response, particularly when targeting the AHR to manipulate disease processes.

Aryl hydrocarbon receptor activation alters immune cell populations in the lung and bone marrow during coronavirus infection.

Respiratory viral infections are one of the major causes of illness and death worldwide. Symptoms associated with respiratory infections can range from mild to severe, and there is limited understanding of why there is large variation in severity. Environmental exposures are a potential causative factor. The aryl hydrocarbon receptor (AHR) is an environment-sensing molecule expressed in all immune cells. Although there is considerable evidence that AHR signaling influences immune responses to other immune challenges, including respiratory pathogens, less is known about the impact of AHR signaling on immune responses during coronavirus (CoV) infection. In this study, we report that AHR activation significantly altered immune cells in the lungs and bone marrow of mice infected with a mouse CoV. AHR activation transiently reduced the frequency of multiple cells in the mononuclear phagocyte system, including monocytes, interstitial macrophages, and dendritic cells in the lung. In the bone marrow, AHR activation altered myelopoiesis, as evidenced by a reduction in granulocyte-monocyte progenitor cells and an increased frequency of myeloid-biased progenitor cells. Moreover, AHR activation significantly affected multiple stages of the megakaryocyte lineage. Overall, these findings indicate that AHR activation modulates multiple aspects of the immune response to a CoV infection. Given the significant burden of respiratory viruses on human health, understanding how environmental exposures shape immune responses to infection advances our knowledge of factors that contribute to variability in disease severity and provides insight into novel approaches to prevent or treat disease.NEW & NOTEWORTHY Our study reveals a multifaceted role for aryl hydrocarbon receptor (AHR) signaling in the immune response to coronavirus (CoV) infection. Sustained AHR activation during in vivo mouse CoV infection altered the frequency of mature immune cells in the lung and modulated emergency hematopoiesis, specifically myelopoiesis and megakaryopoiesis, in bone marrow. This provides new insight into immunoregulation by the AHR and extends our understanding of how environmental exposures can impact host responses to respiratory viral infections.

Unbiased whole genome detection of ultrarare off-target mutations in genome-edited cell populations by HiFi sequencing.

DNA base editors (BEs) composed of a nuclease-deficient Cas9 fused to a DNA-modifying enzyme can achieve on-target mutagenesis without creating double-strand DNA breaks (DSBs). As a result, BEs generate far less DNA damage than traditional nuclease-proficient Cas9 systems, which do rely on the creation of DSBs to achieve on-target mutagenesis. The inability of BEs to create DSBs makes the detection of their undesired off-target effects very difficult. PacBio HiFi sequencing can efficiently detect ultrarare mutations resulting from chemical mutagenesis in whole genomes with a sensitivity ~1 × 10-8 mutations per base pair. In this proof-of-principle study, we evaluated whether this technique could also detect the on- and off-target mutations generated by a cytosine-to-thymine (C>T) BE targeting the LacZ gene in Escherichia coli (E. coli). HiFi sequencing detected on-target mutant allele fractions ranging from ~7% to ~63%, depending on the single-guide RNA (sgRNA) used, while no on-target mutations were detected in controls lacking the BE. The presence of the BE resulted in a ~3-fold increase in mutation frequencies compared to controls lacking the BE, irrespective of the sgRNA used. These increases were mostly composed of C:G>T:A substitutions distributed throughout the genome. Our results demonstrate that HiFi sequencing can efficiently identify on- and off-target mutations in cell populations that have undergone genome editing.

Fluorescence quenching of various indoles by nickel complexes.

The interactions between two nickel complexes with the ligand N,N'-bis (2-pyridylmethylene)-1,3-diaminopropyl and the indoles melatonin, serotonin, tryptamine, and tryptophol were characterized using UV-vis and fluorescence spectroscopy. The fluorescence of all the indoles were quenched in the presence of the complex with a hydroxyl group, indicating that hydrogen-bonding is a necessary interaction for quenching to occur. Various quenching parameters were determined using Stern-Volmer analysis and the quenching was determined to be of a mixed nature with high static quenching values (1011-1013 M-1). Additional analysis using the finite sink approximation indicated that the bimolecular reactions were not diffusion-limited and had high activation energies (135-199 kJ mol-1).