Both higher- and lower-affinity self-reactive CD4+ T cells are expanded in autoimmunity; however, their individual contribution to disease remains unclear. We addressed this question using peptide-MHCII chimeric antigen receptor (pMHCII-CAR) T cells to specifically deplete peptide-reactive T cells in mice. Integration of improvements in CAR engineering with TCR repertoire analysis was critical for interrogating in vivo the role of TCR affinity in autoimmunity. Our original MOG35-55 pMHCII-CAR, which targeted only higher-affinity TCRs, could prevent the induction of experimental autoimmune encephalomyelitis (EAE). However, pMHCII-CAR enhancements to pMHCII stability, as well as increased survivability via overexpression of a dominant-negative Fas, were required to target lower-affinity MOG-specific T cells and reverse ongoing clinical EAE. Thus, these data suggest a model in which higher-affinity autoreactive T cells are required to provide the "activation energy" for initiating neuroinflammatory injury, but lower-affinity cells are sufficient to maintain ongoing disease.

Currently, there is a lack of understanding on the variations of the indoor airborne microbiotas of different building types within a city, and how operational taxonomic unit (OTU)- and amplicon sequence variant (ASV)-based analyses of the 16S rRNA gene sequences affect interpretation of the indoor airborne microbiota results. Therefore, in this study, the indoor airborne bacterial microbiotas between commercial buildings, residences, and subways within the same city were compared using both OTU- and ASV-based analytic methods. Our findings suggested that indoor airborne bacterial microbiota compositions were significantly different between building types regardless of the bioinformatics method used. The processes of ecological drift and random dispersal consistently played significant roles in the assembly of the indoor microbiota across building types. Abundant taxa tended to be more centralized in the correlation network of each building type, highlighting their importance. Taxonomic changes between the microbiotas of different building types were also linked to changes in their inferred metabolic function capabilities. Overall, the results imply that customized strategies are necessary to manage indoor airborne bacterial microbiotas for each building type or even within each specific building.

Studies of the indoor airborne microbiome have mostly been confined to a single location and time point. Here, we characterized, over the course of a year, the geographic variation, building-function dependence, and dispersal characteristics of indoor and outdoor airborne microbiomes (bacterial members only) of eight mechanically ventilated commercial buildings. Based on the Sloan neutral model, airborne microbiomes were randomly dispersed in the respective indoor and outdoor environments and between the two environments during each season. The dominant taxa in the indoor and outdoor environments showed minor variations at each location among seasons. The airborne microbiomes displayed weak seasonality for both indoor and outdoor environments, while a weak geographic variation was found only for the indoor environments. Source tracking results show that outdoor air and occupant skin were major contributors to the indoor airborne microbiomes, but the extent of the contribution from each source varied within and among buildings over the seasons, which suggests variations in local building use. Based on 32 cases of indoor airborne microbiome data, we determined that the indoor/outdoor (I/O) ratio of PM2.5 was not a robust indicator of the sources found indoors. Alternatively, the indoor concentration of carbon dioxide was more closely correlated with the major sources of the indoor airborne microbiome in mechanically ventilated environments.

Metabolically active bacteria within built environments are poorly understood. This study aims to investigate the active airborne bacterial microbiota and compare the total and active microbiota in eight mechanically ventilated buildings over four consecutive seasons using the 16S rRNA gene (rDNA) and the 16S rRNA (rRNA), respectively. The relative abundances of the taxa of presumptive occupants and environmental origins were significantly different between the active and total microbiota. The Sloan neutral model suggested that ecological drift and random dispersal played a smaller role in the assembly of the active microbiota than the total microbiota. The seasonal nature of the active microbiota was consistent with that of the total microbiota in both indoor and outdoor environments, while only the indoor environment was significantly affected by geography. The relative abundances of the active and total taxa were positively correlated, suggesting that the high-abundance members were also the greatest contributors to the community-level metabolic activity. Based on the rRNA/rDNA ratio, the low-abundance members consistently had a higher taxon-level metabolic activity than the high-abundance members over seasons, suggesting that the low-abundance members may have the ability to survive and thrive in the indoor environment and their impact on the health of occupants cannot be overlooked.

ZBTB32 is a transcription factor that is highly expressed by a subset of memory B cells and restrains the magnitude and duration of recall responses against hapten-protein conjugates. To define physiological contexts in which ZBTB32 acts, we assessed responses by Zbtb32−/− mice or bone marrow chimeras against a panel of chronic and acute challenges. Mixed bone marrow chimeras were established in which all B cells were derived from either Zbtb32−/− mice or control littermates. Chronic infection of Zbtb32−/− chimeras with murine cytomegalovirus led to nearly 20-fold higher antigen-specific IgG2b levels relative to controls by week 9 post-infection, despite similar viral loads. In contrast, IgA responses and specificities in the intestine, where memory B cells are repeatedly stimulated by commensal bacteria, were similar between Zbtb32−/− mice and control littermates. Finally, an infection and heterologous booster vaccination model revealed no role for ZBTB32 in restraining primary or recall antibody responses against influenza viruses. Thus, ZBTB32 does not limit recall responses to a number of physiological acute challenges, but does restrict antibody levels during chronic viral infections that periodically engage memory B cells. This restriction might selectively prevent recall responses against chronic infections from progressively overwhelming other antibody specificities.

The development of T cell tolerance in the thymus requires the presentation of host proteins by multiple antigen-presenting-cell (APC) types. However, the importance of transferring host antigens from transcription factor AIRE-dependent medullary thymic epithelial cells (mTECs) to bone marrow (BM) APCs is unknown. We report that antigen was primarily transferred from mTECs to CD8α+ dendritic cells (DCs) and showed that CD36, a scavenger receptor selectively expressed on CD8α+ DCs, mediated the transfer of cell-surface, but not cytoplasmic, antigens. The absence of CD8α+ DCs or CD36 altered thymic T cell selection, as evidenced by TCR repertoire analysis and the loss of allo-tolerance in murine allogeneic BM transplantation (allo-BMT) studies. Decreases in these DCs and CD36 expression in peripheral blood of human allo-BMT patients correlated with graft-vs-host disease. Our findings suggest that CD36 facilitates transfer of mTEC-derived cell-surface antigen on CD8α+ DCs to promote tolerance to host antigens during homeostasis and allo-BMT.

The development of T cell tolerance in the thymus requires the presentation of host proteins by multiple antigen-presenting cell (APC) types. However, the importance of transferring host antigens from transcription factor AIRE-dependent medullary thymic epithelial cells (mTECs) to bone marrow (BM) APCs is unknown. We report that antigen was primarily transferred from mTECs to CD8α+ dendritic cells (DCs) and showed that CD36, a scavenger receptor selectively expressed on CD8α+ DCs, mediated the transfer of cell-surface, but not cytoplasmic, antigens. The absence of CD8α+ DCs or CD36 altered thymic T cell selection, as evidenced by TCR repertoire analysis and the loss of allo-tolerance in murine allogeneic BM transplantation (allo-BMT) studies. Decreases in these DCs and CD36 expression in peripheral blood of human allo-BMT patients correlated with graft-versus-host disease. Our findings suggest that CD36 facilitates transfer of mTEC-derived cell-surface antigen on CD8α+ DCs to promote tolerance to host antigens during homeostasis and allo-BMT.

Trillions of commensal bacteria cohabit our bodies to mutual benefit. In the past several years, it has become clear that the adaptive immune system is not ignorant of intestinal commensal bacteria, but is constantly interacting with them. For T cells, the response to commensal bacteria does not appear uniform, as certain commensal bacterial species appear to trigger effector T cells to reject and control them, whereas other species elicit Foxp3 + regulatory T (Treg) cells to accept and be tolerant of them. Here, we review our current knowledge of T cell differentiation in response to commensal bacteria, and how this process leads to immune homeostasis in the intestine.