The Fates of Dendritic Cells and Antigen Regulate CD4+ T Cell Responses

<p>The rapid activation of effector T cells by antigen-presenting dendritic cells (DCs) is necessary to contain and eradicate pathogens. Upon eradication of the pathogens by effector T cells, the immune response eventually resolves, and the clearance of residual antigen is necessary to prevent immune cell exhaustion or immunopathology. It has been proposed that the elimination of antigen-presenting DCs by CD8+ cytotoxic T cells (CTLs) limits the duration of antigen presentation, hence resolving ongoing immune responses. However, inter-DC antigen transfer spreads antigens for further antigen presentation and may reduce the effect of CTL-mediated DC killing. The aim of my thesis was to examine the impact of CTL-mediated DC killing and inter-DC antigen transfer on the induction and the quality of resulting T cell responses. Initial experiments established that CTLs eliminated antigen-bearing DCs mainly through the cytolytic molecule perforin, whereas FasL played a minor role. CTL-mediated DC killing prevented antigen-bearing DCs from stimulating naive CD4+ and CD8+ T cells in the draining lymph nodes. Thus, CTLs regulated the clonal expansion of naive T cells by controlling the survival of antigen-presenting DCs. The efficiency of CTL-mediated DC killing depended on the method of antigen loading onto DCs, and to a lesser extent, the method of generating CTLs. Surprisingly, efficient CTL-mediated DC killing that completely prevented the accumulation of injected DCs in the lymph nodes did not abolish T cell proliferation, indicating that other antigen presenting cells (APCs) were inducing the residual T cell proliferation when the antigen-bearing DCs were eliminated by CTLs. Further investigations revealed that the antigen from the injected DCs was transferred to host DCs. In the absence of direct antigen presentation by injected DCs, host DCs stimulated local T cell proliferation but did not induce a systemic effector T cell response. In contrast, in the presence of efficient CTL-mediated DC killing, inter-DC antigen transfer enabled the host DCs to stimulate T cell proliferation. These T cells then developed into iii functional effector T cells. In conclusion, in the absence of inter-DC antigen transfer, CTLmediated DC killing reduces the size of T cell responses. However, in the presence of inter- DC antigen transfer, the impact of CTL-mediated DC killing is reduced, hence influencing the size and quality of T cell responses. My findings shed light on how CTL-mediated DC killing and inter-DC antigen transfer regulate immune responses and how DC vaccine regimens for immunotherapy can be improved.</p>

The Fates of Dendritic Cells and Antigen Regulate CD4+ T Cell Responses

<p>The rapid activation of effector T cells by antigen-presenting dendritic cells (DCs) is necessary to contain and eradicate pathogens. Upon eradication of the pathogens by effector T cells, the immune response eventually resolves, and the clearance of residual antigen is necessary to prevent immune cell exhaustion or immunopathology. It has been proposed that the elimination of antigen-presenting DCs by CD8+ cytotoxic T cells (CTLs) limits the duration of antigen presentation, hence resolving ongoing immune responses. However, inter-DC antigen transfer spreads antigens for further antigen presentation and may reduce the effect of CTL-mediated DC killing. The aim of my thesis was to examine the impact of CTL-mediated DC killing and inter-DC antigen transfer on the induction and the quality of resulting T cell responses. Initial experiments established that CTLs eliminated antigen-bearing DCs mainly through the cytolytic molecule perforin, whereas FasL played a minor role. CTL-mediated DC killing prevented antigen-bearing DCs from stimulating naive CD4+ and CD8+ T cells in the draining lymph nodes. Thus, CTLs regulated the clonal expansion of naive T cells by controlling the survival of antigen-presenting DCs. The efficiency of CTL-mediated DC killing depended on the method of antigen loading onto DCs, and to a lesser extent, the method of generating CTLs. Surprisingly, efficient CTL-mediated DC killing that completely prevented the accumulation of injected DCs in the lymph nodes did not abolish T cell proliferation, indicating that other antigen presenting cells (APCs) were inducing the residual T cell proliferation when the antigen-bearing DCs were eliminated by CTLs. Further investigations revealed that the antigen from the injected DCs was transferred to host DCs. In the absence of direct antigen presentation by injected DCs, host DCs stimulated local T cell proliferation but did not induce a systemic effector T cell response. In contrast, in the presence of efficient CTL-mediated DC killing, inter-DC antigen transfer enabled the host DCs to stimulate T cell proliferation. These T cells then developed into iii functional effector T cells. In conclusion, in the absence of inter-DC antigen transfer, CTLmediated DC killing reduces the size of T cell responses. However, in the presence of inter- DC antigen transfer, the impact of CTL-mediated DC killing is reduced, hence influencing the size and quality of T cell responses. My findings shed light on how CTL-mediated DC killing and inter-DC antigen transfer regulate immune responses and how DC vaccine regimens for immunotherapy can be improved.</p>

Antigen cross-presentation by macrophages

В обзоре рассматриваются механизмы кросс-презентации антигена и особенности этого процесса в макрофагах. Представлено сравнение особенностей кросс-презентации в дендритных клетках и разных фенотипах макрофагов. Описаны пути кросс-презентации -протеасомный и вакуолярный. Протеасомный путь состоит из следующих стадий: 1) захват антигена в фагосому; 2) сохранение антигена в фагосоме; 3) перенос антигена в цитозоль и его расщепление в протеасоме до олигопептидов; 4) перенос олигопептидов в компартменты, содержащие главный комплекс гистосовместимости I типа (major histocompatibility complex I, MHC I); 5) загрузка олигопептида на MHC-I и перенос на поверхность клетки. Вакуолярный путь начинается сходно с протеасомным, но отличается в том, что захваченный антиген не покидает фагосому, а там же расщепляется и нагружается на MHC-I. Макрофаги могут использовать любой из этих путей. Макрофаги, происходящие из моноцитов крови, используют вакуолярный путь, макрофаги красной пульпы селезенки - протеасомный, а перитонеальные - и тот, и другой. Эффективность кросс-презентации макрофагов зависит от его тканевого типа. При разработке методов иммунотерапии, основанной на макрофагах, важно понимать стадии обоих путей кросс-презентации, поскольку каждая из них может рассматриваться как мишень для повышения эффективности кросс-презентации антигена и соответственно, эффективности иммунотерапии рака. This review focuses on mechanisms of antigen cross-presentation and features of this process in macrophages. Features of the cross-presentation in dendritic cells and in various macrophage phenotypes are compared. The cross-presentation can be the result of either the proteasomal or vacuolar pathway. The proteasomal pathway includes the following stages: 1) antigen capture into the phagosome; 2) antigen preservation in the phagosome; 3) antigen transfer to the cytosol and its cleavage in the proteasome to oligopeptides; 4) oligopeptide transfer into major histocompatibility complex (MHC) I-containing compartments; 5) oligopeptide loading onto the MHC I and transferring it to the cell surface. The vacuolar pathway begins in a similar way as the proteasomal pathway but differs in that the captured antigen does not leave the phagosome, but is cleaved there and loaded onto MHC I. Macrophages can use any of these pathways. Macrophages originating from blood monocytes use the vacuolar pathway; macrophages of the red pulp of the spleen use the proteasomal pathway, and peritoneal macrophages use both. The effectiveness of cross-presentation of macrophages depends on the macrophage tissue type. When developing macrophage-based methods of immunotherapy, it is important to understand the stages of both cross-presentation pathways since each of them can be considered as a target for increasing the efficiency of antigen cross-presentation and, accordingly, the effectiveness of cancer immunotherapy.

A model of preferential pairing between epithelial and dendritic cells in thymic antigen transfer

Medullary thymic epithelial cells (mTECs) which produce and present self-antigens are essential for the establishment of central tolerance. Since mTEC numbers are limited, their function is complemented by thymic dendritic cells (DCs), which transfer mTEC-produced self-antigens via cooperative antigen transfer (CAT). While CAT is required for effective T cell selection, many aspects remain enigmatic. Given the recently described heterogeneity of mTECs and DCs, it is unclear whether the antigen acquisition from a particular TEC subset is mediated by preferential pairing with specific subset of DCs. Using several relevant Cre-based mouse models controlling the expression of fluorescent proteins, we found that in regards to CAT, each subset of thymic DCs preferentially targets distinct mTEC subset(s) and importantly, XCR1+ activated DCs represented the most potent subset in CAT. Interestingly, one thymic DC can acquire antigen repetitively and of these, monocyte-derived DCs (moDC) were determined to be the most efficient in repetitive CAT. moDCs also represented the most potent DC subset in the acquisition of antigen from other DCs. These findings suggest a preferential pairing model for the distribution of mTEC-derived antigens among distinct populations of thymic DCs.

History of the Rhesus factor and of neonatal jaundice

The history of icterus and neonatal jaundice has been recorded since the 17th century, when a French midwife first described jaundice (jaune) in twins. In 1940, Alexander Wiener and Karl Landsteiner discovered the Rh blood group, and they investigated the isoimmunization via antigen transfer across the placenta from the fetus. Other blood group systems implicated in isoimmunization were discovered between 1901 and 1965. Between 1940-1960, many studies have focused on the etiology of hemolytic disease of the newborn, on incompatibility in the Rh system, cholestasis, metabolic diseases, inhibitors of breast milk, and the association between prematurity and jaun-dice or extremely nuclear jaundice. It is the merit of AW Liley, in 1963, who described the diagram of the same name based on the level of bilirubin in the amniotic fluid and who performed the first fetal transfusions for fetal anemia. Last decades, non-invasive methods of diagnosis and treatment were described.

Involvement of Astrocytes and microRNA Dysregulation in Neurodegenerative Diseases: From Pathogenesis to Therapeutic Potential

Astrocytes are the most widely distributed and abundant glial cells in the central nervous system (CNS). Neurodegenerative diseases (NDDs) are a class of diseases with a slow onset, progressive progression, and poor prognosis. Common clinical NDDs include Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington’s disease (HD). Although these diseases have different etiologies, they are all associated with neuronal loss and pathological dysfunction. Accumulating evidence indicates that neurotransmitters, neurotrophic factors, and toxic metabolites that are produced and released by activated astrocytes affect and regulate the function of neurons at the receptor, ion channel, antigen transfer, and gene transcription levels in the pathogenesis of NDDs. MicroRNAs (miRNAs) are a group of small non-coding RNAs that play a wide range of biological roles by regulating the transcription and post-transcriptional translation of target mRNAs to induce target gene expression and silencing. Recent studies have shown that miRNAs participate in the pathogenesis of NDDs by regulating astrocyte function through different mechanisms and may be potential targets for the treatment of NDDs. Here, we review studies of the role of astrocytes in the pathogenesis of NDDs and discuss possible mechanisms of miRNAs in the regulation of astrocyte function, suggesting that miRNAs may be targeted as a novel approach for the treatment of NDDs.

Plasmacytoid dendritic cells cross-prime naive CD8 T cells by transferring antigen to conventional dendritic cells through exosomes

Although plasmacytoid dendritic cells (pDCs) have been shown to play a critical role in generating viral immunity and promoting tolerance to suppress antitumor immunity, whether and how pDCs cross-prime CD8 T cells in vivo remain controversial. Using a pDC-targeted vaccine model to deliver antigens specifically to pDCs, we have demonstrated that pDC-targeted vaccination led to strong cross-priming and durable CD8 T cell immunity. Surprisingly, cross-presenting pDCs required conventional DCs (cDCs) to achieve cross-priming in vivo by transferring antigens to cDCs. Taking advantage of an in vitro system where only pDCs had access to antigens, we further demonstrated that cross-presenting pDCs were unable to efficiently prime CD8 T cells by themselves, but conferred antigen-naive cDCs the capability of cross-priming CD8 T cells by transferring antigens to cDCs. Although both cDC1s and cDC2s exhibited similar efficiency in acquiring antigens from pDCs, cDC1s but not cDC2s were required for cross-priming upon pDC-targeted vaccination, suggesting that cDC1s played a critical role in pDC-mediated cross-priming independent of their function in antigen presentation. Antigen transfer from pDCs to cDCs was mediated by previously unreported pDC-derived exosomes (pDCexos), that were also produced by pDCs under various conditions. Importantly, all these pDCexos primed naive antigen-specific CD8 T cells only in the presence of bystander cDCs, similarly to cross-presenting pDCs, thus identifying pDCexo-mediated antigen transfer to cDCs as a mechanism for pDCs to achieve cross-priming. In summary, our data suggest that pDCs employ a unique mechanism of pDCexo-mediated antigen transfer to cDCs for cross-priming.

Perivascular dendritic cells elicit anaphylaxis by relaying allergens to mast cells via microvesicles

Anaphylactic reactions are triggered when allergens enter the blood circulation and activate immunoglobulin E (IgE)–sensitized mast cells (MCs), causing systemic discharge of prestored proinflammatory mediators. As MCs are extravascular, how they perceive circulating allergens remains a conundrum. Here, we describe the existence of a CD301b+ perivascular dendritic cell (DC) subset that continuously samples blood and relays antigens to neighboring MCs, which vigorously degranulate and trigger anaphylaxis. DC antigen transfer involves the active discharge of surface-associated antigens on 0.5- to 1.0-micrometer microvesicles (MVs) generated by vacuolar protein sorting 4 (VPS4). Antigen sharing by DCs is not limited to MCs, as neighboring DCs also acquire antigen-bearing MVs. This capacity of DCs to distribute antigen-bearing MVs to various immune cells in the perivascular space potentiates inflammatory and immune responses to blood-borne antigens.