New insights into the germline genes and CDR3 repertoire of the TCRβ chain in Chiroptera

Studying bats using a One Health lens: bridging the gap between bat virology and disease ecology

Accumulating data suggest that some bat species host emerging viruses that are highly pathogenic in humans and agricultural animals. Laboratory-based studies have highlighted important adaptations in bat immune systems that allow them to better tolerate viral infections compared to humans. Simultaneously, ecological studies have discovered critical extrinsic factors, such as nutritional stress, that correlate with virus shedding in wild-caught bats. Despite some progress in independently understanding the role of bats as reservoirs of emerging viruses, there remains a significant gap in the molecular understanding of factors that drive virus spillover from bats. Driven by a collective goal of bridging the gap between the fields of bat virology, immunology, and disease ecology, we hosted a satellite symposium at the 2024 American Society for Virology meeting. Bringing together virologists, immunologists, and disease ecologists, we discussed the intrinsic and extrinsic factors such as virus receptor engagement, adaptive immunity, and virus ecology that influence spillover from bat hosts. This article summarizes the topics discussed during the symposium and emphasizes the need for interdisciplinary collaborations and resource sharing.

HTS and scRNA-seq revealed that the location and RSS quality of the mammalian TRBV and TRBJ genes impact biased rearrangement

The quality of Recombination signal sequences (RSSs), location, and genetics of mammalian V, D, and J genes synergistically affect the recombination frequency of genes; however, the specific regulatory mechanism and efficiency have not been elucidated. By taking advantage of single-cell RNA-sequencing (scRNA-seq) and high-throughput sequencing (HTS) to investigate V(D)J rearrangement characteristics in the CDR3 repertoire, we found that the distal and proximal V genes (or J genes) "to D" gene were involved in rearrangement significantly more frequently than the middle V genes (or J genes) in the TRB locus among various species, including Primates (human and rhesus monkey), Rodentia (BALB/c, C57BL/6, and Kunming mice), Artiodactyla (buffalo), and Chiroptera (Rhinolophus affinis). The RSS quality of the V and J genes affected their frequency in rearrangement to varying degrees, especially when the V-RSSs with recombination signal information content (RIC) score < -45 significantly reduced the recombination frequency of the V gene. The V and J genes that were "away from D" had the dual advantages of recombinant structural accessibility and relatively high-quality RSSs, which promoted their preferential utilization in rearrangement. The quality of J-RSSs formed during mammalian evolution was apparently greater than that of V-RSSs, and the D-J distance was obviously shorter than that of V-D, which may be one of the reasons for guaranteeing that the "D-to-J preceding V-to-DJ rule" occurred when rearranged. This study provides a novel perspective on the mechanism and efficiency of V-D-J rearrangement in the mammalian TRB locus, as well as the biased utilization characteristics and application of V and J genes in the initial CDR3 repertoire.

The reverse TRBV30 gene of mammals: a defect or superiority in evolution?

At the 3' end of the C2 gene in the mammalian TRB locus, a distinct reverse TRBV30 gene (named TRBV31 in mice) has been conserved throughout evolution. In the fully annotated TRB locus of 14 mammals (including six orders), we observed noteworthy variations in the localization and quality of the reverse V30 genes and Recombination Signal Sequences (RSSs) in the gene trees of 13 mammals. Conversely, the forward V29 genes and RSSs were generally consistent with the species tree of their corresponding species. This finding suggested that the evolution of the reverse V30 gene was not synchronous and likely played a crucial role in regulating adaptive immune responses. To further investigate this possibility, we utilized single-cell TCR sequencing (scTCR-seq) and high-throughput sequencing (HTS) to analyze TCRβ CDR3 repertoires from both central and peripheral tissues of Primates (Homo sapiens and Macaca mulatta), Rodentia (Mus musculus: BALB/c, C57BL/6, and Kunming mice), Artiodactyla (Bos taurus and Bubalus bubalis), and Chiroptera (Rhinolophus affinis and Hipposideros armige). Our investigation revealed several novel observations: (1) The reverse V30 gene exhibits classical rearrangement patterns adhering to the '12/23 rule' and the 'D-J rearrangement preceding the V-(D-J) rearrangement'. This results in the formation of rearranged V30-D2J2, V30-D1J1, and V30-D1J2. However, we also identified 'special rearrangement patterns' wherein V30-D rearrangement preceding D-J rearrangement, giving rise to rearranged V30-D2-J1 and forward Vx-D2-J. (2) Compared to the 'deletional rearrangement' (looping out) of forward V1-V29 genes, the reverse V30 gene exhibits preferential utilization with 'inversional rearrangement'. This may be attributed to the shorter distance between the V30 gene and D gene and the 'inversional rearrangement' modes. In summary, in the mammalian TRB locus, the reverse V30 gene has been uniquely preserved throughout evolution and preferentially utilized in V(D)J recombination, potentially serving a significant role in adaptive immunity. These results will pave the way for novel and specialized research into the mechanisms, efficiency, and function of V(D)J recombination in mammals.

Different species of Chiroptera: Immune cells and molecules

The distinct composition and immune response characteristics of bats' innate and adaptive immune systems, which enable them to serve as host of numerous serious zoonotic viruses without falling ill, differ substantially from those of other mammals, it have garnered significant attention. In this article, we offer a systematic review of the names, attributes, and functions of innate and adaptive immune cells & molecules across different bat species. This includes descriptions of the differences shown by research between 71 bat species in 10 families, as well as comparisons between bats and other mammals. Studies of the immune cells & molecules of different bat species are necessary to understand the unique antiviral immunity of bats. By providing comprehensive information on these unique immune responses, it is hoped that new insights will be provided for the study of co-evolutionary dynamics between viruses and the bat immune system, as well as human antiviral immunity.

Advances in understanding bat infection dynamics across biological scales

Over the past two decades, research on bat-associated microbes such as viruses, bacteria and fungi has dramatically increased. Here, we synthesize themes from a conference symposium focused on advances in the research of bats and their microbes, including physiological, immunological, ecological and epidemiological research that has improved our understanding of bat infection dynamics at multiple biological scales. We first present metrics for measuring individual bat responses to infection and challenges associated with using these metrics. We next discuss infection dynamics within bat populations of the same species, before introducing complexities that arise in multi-species communities of bats, humans and/or livestock. Finally, we outline critical gaps and opportunities for future interdisciplinary work on topics involving bats and their microbes.