HIV-1-Infected CD4+ T Cells Present MHC Class II-Restricted Epitope via Endogenous Processing.

HIV-1-specific CD4+ T cells (TCD4+s) play a critical role in controlling HIV-1 infection. Canonically, TCD4+s are activated by peptides derived from extracellular ("exogenous") Ags displayed in complex with MHC class II (MHC II) molecules on the surfaces of "professional" APCs such as dendritic cells (DCs). In contrast, activated human TCD4+s, which express MHC II, are not typically considered for their APC potential because of their low endocytic capacity and the exogenous Ag systems historically used for assessment. Using primary TCD4+s and monocyte-derived DCs from healthy donors, we show that activated human TCD4+s are highly effective at MHC II-restricted presentation of an immunodominant HIV-1-derived epitope postinfection and subsequent noncanonical processing and presentation of endogenously produced Ag. Our results indicate that, in addition to marshalling HIV-1-specific immune responses during infection, TCD4+s also act as APCs, leading to the activation of HIV-1-specific TCD4+s.

Human erythroid progenitors express antigen presentation machinery.

Early-life immune exposures can profoundly impact lifelong health. However, functional mechanisms underlying fetal immune development remain incomplete. Erythrocytes are not typically considered active immune mediators, primarily because erythroid precursors discard their organelles as they mature, thus losing the ability to alter gene expression in response to stimuli. Erythroid progenitors and precursors circulate in human fetuses and neonates. Although there is limited evidence that erythroid precursors are immunomodulatory, our understanding of the underlying mechanisms remains inadequate. To define the immunobiological role of fetal and perinatal erythroid progenitors and precursors, we analyzed single cell RNA-sequencing data and found that transcriptomics support erythroid progenitors as putative immune mediators. Unexpectedly, we discovered that human erythroid progenitors constitutively express Major Histocompatibility Complex (MHC) class II antigen processing and presentation machinery, which are hallmarks of specialized antigen presenting immune cells. Furthermore, we demonstrate that erythroid progenitors internalize and cleave foreign proteins into peptide antigens. Unlike conventional antigen presenting cells, erythroid progenitors express atypical costimulatory molecules and immunoregulatory cytokines that direct the development of regulatory T cells, which are critical for establishing maternal-fetal tolerance. Expression of MHC II in definitive erythroid progenitors begins during the second trimester, coinciding with the appearance of mature T cells in the fetus, and is absent in primitive progenitors. Lastly, we demonstrate physical and molecular interaction potential of erythroid progenitors and T cells in the fetal liver. Our findings shed light on a unique orchestrator of fetal immunity and provide insight into the mechanisms by which erythroid cells contribute to host defense.

Recombinant Poxviruses: Versatile Tools for Immunological Assays.

The study of antigen processing and presentation is critical to our understanding of the mechanisms that govern immune surveillance. A typical requirement of assays designed to examine antigen processing and presentation is the de novo biosynthesis of a model antigen. Historically, Vaccinia virus, a poxvirus closely related to Cowpox virus, has enjoyed widespread use for this purpose. Recombinant poxvirus-based expression has a number of advantages over other systems. Poxviruses accommodate the insertion of large pieces of recombinant DNA into their genome, and recombination and selection are relatively efficient. Poxviruses readily infect a variety of cell types, and they drive rapid and high levels of antigen expression. Additionally, they can be utilized in a variety of assays to study both MHC class I restricted and MHC class II restricted antigen processing and presentation. Ultimately, the numerous advantages of poxvirus recombinants have made the Vaccinia expression system a mainstay in the study of processing and presentation over the past two decades. In an attempt to address one shortcoming of Vaccinia virus while simultaneously retaining the benefits inherent to poxviruses, our laboratory has begun to engineer recombinant Ectromelia viruses. Ectromelia virus, or mousepox, is a natural pathogen of murine cells and performing experiments in the context of a natural host-pathogen relationship may elucidate unknown factors that influence epitope generation and host response. This chapter will describe several recombinant poxvirus system protocols used to study both MHC class I and class II antigen processing and presentation, as well as provide insight and troubleshooting techniques to improve the reproducibility and fidelity of these experiments.

Human MAIT cells exit peripheral tissues and recirculate via lymph in steady state conditions.

Mucosal-associated invariant T cells (MAIT cells) recognize bacterial metabolites as antigen and are found in blood and tissues, where they are poised to contribute to barrier immunity. Recent data demonstrate that MAIT cells located in mucosal barrier tissues are functionally distinct from their blood counterparts, but the relationship and circulation of MAIT cells between blood and different tissue compartments remains poorly understood. Previous studies raised the possibility that MAIT cells do not leave tissue and may either be retained or undergo apoptosis. To directly address if human MAIT cells exit tissues, we collected human donor-matched thoracic duct lymph and blood and analyzed MAIT cell phenotype, transcriptome, and T cell receptor (TCR) diversity by flow cytometry and RNA sequencing. We found that MAIT cells were present in the lymph, despite being largely CCR7- in the blood, thus indicating that MAIT cells in the lymph migrated from tissues and were capable of exiting tissues to recirculate. Importantly, MAIT cells in the lymph and blood had highly overlapping clonotype usage but distinct transcriptome signatures, indicative of differential activation states.

Stranger and acquaintance sexual assault of adult males.

This study examined victim and assault characteristics and the nature and extent of coercion, violence, and physical injuries among adult male victims of sexual assaults. Client records of three groups presenting to a sexual assault care center were included: males assaulted by a stranger (n = 64), males assaulted by an acquaintance (n = 81), and females assaulted by an acquaintance (n = 106). Study results revealed that male victims of sexual assault tended to be young, single men who reported high rates of vulnerabilities such as homelessness and physical, psychiatric, and cognitive disabilities. Male stranger assailant victims were more likely to experience assaults involving weapons and physical violence. Injuries sustained by victims and services delivered at the sexual assault care center were similar for both male and female clients. The results of this study reveal new information about violence in male sexual assaults and the vulnerability of the male victims.

Immediate and delayed treatment seeking among adult sexual assault victims.

There is a growing body of literature which seeks to better understand the needs of sexual assault victims presenting for specialized treatment. This study explored aspects of immediate and delayed treatment seeking among 1118 women who presented for treatment to a specialized sexual assault care centre within a large urban hospital. Variables related to demographic and assault-specific characteristics were examined for association with immediate (within 12 hours) or delayed (after 12 hours) treatment seeking. Results indicate the severity of the attack prompted women to seek treatment earlier and that women who were assaulted by a known perpetrator were more likely to delay seeking assistance. Findings are conceptualized under the rubric of sociological and feminist frameworks with suggestions for additional research.

Acute forensic medical procedures used following a sexual assault among treatment-seeking women.

Despite the negative physical and mental health outcomes of sexual assault, a minority of sexually assaulted women seek immediate post-assault medical and legal services. This study identified the number and types of acute forensic medical procedures used by women presenting at a hospital-based urgent care centre between 1997 and 2001 within 72 hours following a reported sexual assault. The study also examined assault and non-assault factors associated with the use of procedures. It was hypothesized that assault characteristics resembling the stereotype of rape would be associated with the use of more procedures. The multiple regression indicated that injury severity, coercion severity, homelessness, and delay in presentation were significantly associated with the number of procedures received. Findings provide partial support for the hypothesis that post-assault procedures would be associated with the stereotype of rape, and highlight homeless women as a group particularly at risk for not receiving adequate medical treatment following a sexual assault.