Enhanced myelopoiesis and aggravated arthritis in S100a8-deficient mice.

Expressed strongly by myeloid cells, damage-associated molecular pattern (DAMP) proteins S100A8 and S100A9 are found in the serum of patients with infectious and autoimmune diseases. Compared to S100A9, the role of S100A8 is controversial. We investigated its biological activity in collagen-induced arthritis using the first known viable and fertile S100a8-deficient (S100a8-/-) mouse. Although comparable to the wild type (WT) in terms of lymphocyte distribution in blood and in the primary and secondary lymphoid organs, S100a8-/- mice had increased numbers of neutrophils, monocytes and dendritic cells in the blood and bone marrow, and these all expressed myeloid markers such as CD11b, Ly6G and CD86 more strongly. Granulocyte-macrophage common precursors were increased in S100a8-/- bone marrow and yielded greater numbers of macrophages and dendritic cells in culture. The animals also developed more severe arthritic disease leading to aggravated osteoclast activity and bone destruction. These findings were correlated with increased inflammatory cell infiltration and cytokine secretion in the paws. This study suggests that S100A8 is an anti-inflammatory DAMP that regulates myeloid cell differentiation, thereby mitigating the development of experimental arthritis.

The orphan nuclear receptor NR4A3 controls the differentiation of monocyte-derived dendritic cells following microbial stimulation.

In response to microbial stimulation, monocytes can differentiate into macrophages or monocyte-derived dendritic cells (MoDCs) but the molecular requirements guiding these possible fates are poorly understood. In addition, the physiological importance of MoDCs in the host cellular and immune responses to microbes remains elusive. Here, we demonstrate that the nuclear orphan receptor NR4A3 is required for the proper differentiation of MoDCs but not for other types of DCs. Indeed, the generation of DC-SIGN+ MoDCs in response to LPS was severely impaired in Nr4a3-/- mice, which resulted in the inability to mount optimal CD8+ T cell responses to gram-negative bacteria. Transcriptomic analyses revealed that NR4A3 is required to skew monocyte differentiation toward MoDCs, at the expense of macrophages, and allows the acquisition of migratory characteristics required for MoDC function. Altogether, our data identify that the NR4A3 transcription factor is required to guide the fate of monocytes toward MoDCs.

The Notch signaling pathway controls CD8+ T cell differentiation independently of the classical effector HES1.

During CD8+ T cell response, Notch signaling controls short-lived-effector-cell (SLEC) generation, but the exact mechanisms by which it does so remains unclear. The Notch signaling pathway can act as a key regulator of Akt signaling via direct transcriptional induction of Hes1, which will then repress the transcription of Pten, an inhibitor of Akt signaling. As both Notch and Akt signaling can promote effector CD8+ T cell differentiation, we asked whether Notch signaling influences SLEC differentiation via the HES1-PTEN axis. Here, we demonstrate that HES1 deficiency in murine CD8+ T cells did not impact SLEC differentiation. Moreover, we show that Pten transcriptional repression in effector CD8+ T cells is not mediated by Notch signaling although Akt activation requires Notch signaling. Therefore, HES1 is not an effector of Notch signaling during CD8+ T cell response.

Neuropilin-1 expression in adipose tissue macrophages protects against obesity and metabolic syndrome.

Obesity gives rise to metabolic complications by mechanisms that are poorly understood. Although chronic inflammatory signaling in adipose tissue is typically associated with metabolic deficiencies linked to excessive weight gain, we identified a subset of neuropilin-1 (NRP1)-expressing myeloid cells that accumulate in adipose tissue and protect against obesity and metabolic syndrome. Ablation of NRP1 in macrophages compromised lipid uptake in these cells, which reduced substrates for fatty acid ß-oxidation and shifted energy metabolism of these macrophages toward a more inflammatory glycolytic metabolism. Conditional deletion of NRP1 in LysM Cre-expressing cells leads to inadequate adipose vascularization, accelerated weight gain, and reduced insulin sensitivity even independent of weight gain. Transfer of NRP1+ hematopoietic cells improved glucose homeostasis, resulting in the reversal of a prediabetic phenotype. Our findings suggest a pivotal role for adipose tissue-resident NRP1+-expressing macrophages in driving healthy weight gain and maintaining glucose tolerance.

Inflammation enhances the vaccination potential of CD40-activated B cells in mice.

Vaccination with antigen-pulsed CD40-activated B (CD40-B) cells can efficiently lead to the in vivo differentiation of naive CD8+ T cells into fully functional effectors. In contrast to bone marrow-derived dendritic cell (BMDC) vaccination, CD40-B cell priming does not allow for memory CD8+ T-cell generation but the reason for this deficiency is unknown. Here, we show that compared to BMDCs, murine CD40-B cells induce lower expression of several genes regulated by T-cell receptor signaling, costimulation, and inflammation (signals 1-3) in mouse T cells. The reduced provision of signals 1 and 2 by CD40-B cells can be explained by a reduction in the quality and duration of the interactions with naive CD8+ T cells as compared to BMDCs. Furthermore, CD40-B cells produce less inflammatory mediators, such as IL-12 and type I interferon, and increasing inflammation by coadministration of polyriboinosinic-polyribocytidylic acid with CD40-B-cell immunization allowed for the generation of long-lived and functional CD8+ memory T cells. In conclusion, it is possible to manipulate CD40-B-cell vaccination to promote the formation of long-lived functional CD8+ memory T cells, a key step before translating the use of CD40-B cells for therapeutic vaccination.

IL-2 induction of Blimp-1 is a key in vivo signal for CD8+ short-lived effector T cell differentiation.

During infection or vaccination, only a small proportion of CD8(+) T cells differentiate into memory cells. The mechanisms underlying the differentiation of CD8(+) T cells into short-lived effector cells (SLECs) or memory precursor effector cells are poorly defined. It was recently shown in infectious models that the transcriptional repressor B lymphocyte-induced maturation protein 1 (Blimp-1) enhances the formation of SLECs. The factors controlling Blimp-1 expression leading to the in vivo formation of SLECs are still not known. However, it has been shown that cytokines such as IL-2 induce Blimp-1 expression in vitro. In this study, we took advantage of the low-inflammation model of dendritic cell immunization to study the role of the IL-2/Blimp-1 axis in SLEC differentiation as well as the importance of Blimp-1 expression in memory precursor effector cells for proper CD8(+) memory generation. Our results show that Blimp-1 deficiency affects effector differentiation and function in the absence of inflammation. Unexpectedly, memory generation was not affected in Blimp-1-deficient OT-I cells responding to vaccination. In addition, modulation of the bioavailability of IL-2 by injection either of a blocking Ab or of the cytokine, demonstrates a link between IL-2, Blimp-1 induction, and SLEC formation in wild-type cells. Conversely, injection of IL-2 had less effect on Blimp-1-deficient CD8(+) T cells, indicating that the effect of IL-2 on in vivo SLEC differentiation is mediated by Blimp-1. In conclusion, IL-2 induction of Blimp-1 expression is a key regulator of SLEC differentiation in vivo.

The catalytic activity of the mitogen-activated protein kinase extracellular signal-regulated kinase 3 is required to sustain CD4+ CD8+ thymocyte survival.

Extracellular signal-regulated kinase 3 (ERK3) is an atypical member of the mitogen-activated protein kinase (MAPK) family whose function is largely unknown. Given the central role of MAPKs in T cell development, we hypothesized that ERK3 may regulate thymocyte development. Here we have shown that ERK3 deficiency leads to a 50% reduction in CD4(+) CD8(+) (DP) thymocyte number. Analysis of hematopoietic chimeras revealed that the reduction in DP thymocytes is intrinsic to hematopoietic cells. We found that early thymic progenitors seed the Erk3(-/-) thymus and can properly differentiate and proliferate to generate DP thymocytes. However, ERK3 deficiency results in a decrease in the DP thymocyte half-life, associated with a higher level of apoptosis. As a consequence, ERK3-deficient DP thymocytes are impaired in their ability to make successful secondary T cell receptor alpha (TCRα) gene rearrangement. Introduction of an already rearranged TCR transgene restores thymic cell number. We further show that knock-in of a catalytically inactive allele of Erk3 fails to rescue the loss of DP thymocytes. Our results uncover a unique role for ERK3, dependent on its kinase activity, during T cell development and show that this atypical MAPK is essential to sustain DP survival during RAG-mediated rearrangements.

Nanoparticle adjuvant sensing by TLR7 enhances CD8+ T cell-mediated protection from Listeria monocytogenes infection.

Developing new adjuvants and vaccination strategies is of paramount importance to successfully fight against many life-threatening infectious diseases and cancer. Very few adjuvants are currently authorized for human use, and these mainly stimulate a humoral response. However, specific Abs are not sufficient to confer protection against persisting infections or cancer. Therefore, development of adjuvants and immunomodulators able to enhance cell-mediated immune responses represents a major medical need. We recently showed that papaya mosaic virus nanoparticles (PapMV), self-assembled from the coat protein of a plant virus and a noncoding ssRNA molecule, are highly immunogenic in mice. PapMV can be used either as a vaccine delivery platform, through fusion of various epitopes to the coat protein or as adjuvant to enhance humoral immune responses against coadministered Ags or vaccines. However, the mechanisms that confer these immunomodulatory properties to PapMV and its ability to enhance T cell vaccines remain unknown. Using immunization studies in mice, we demonstrate in this paper that PapMV represents a novel TLR7 agonist with strong immunostimulatory properties. More importantly, pretreatment with PapMV significantly improves effector and memory CD8(+) T cell responses generated through dendritic cell vaccination increasing protection against a Listeria monocytogenes challenge.

IL-6 production by dendritic cells is dispensable for CD8+ memory T-cell generation.

Following activation, naïve CD8(+) T cells will differentiate into effectors that differ in their ability to survive: some will persist as memory cells while the majority will die by apoptosis. Signals given by antigen-presenting cells (APCs) at the time of priming modulate this differential outcome. We have recently shown that, in opposition to dendritic cell (DC), CD40-activated B-(CD40-B) cell vaccination fails to efficiently produce CD8(+) memory T cells. Understanding why CD40-B-cell vaccination does not lead to the generation of functional long-lived memory cells is essential to define the signals that should be provided to naïve T cells by APCs. Here we show that CD40-B cells produce very low amount of IL-6 when compared to DCs. However, supplementation with IL-6 during CD40-B-cell vaccination did not improve memory generation. Furthermore, IL-6-deficient DCs maintained the capacity to promote the formation of functional CD8(+) effectors and memory cells. Our results suggest that in APC vaccination models, IL-6 provided by the APCs is dispensable for proper CD8(+) T-cell memory generation.

CD40-activated B cells can efficiently prime antigen-specific naïve CD8+ T cells to generate effector but not memory T cells.

BACKGROUND: The identification of the signals that should be provided by antigen-presenting cells (APCs) to induce a CD8(+) T cell response in vivo is essential to improve vaccination strategies using antigen-loaded APCs. Although dendritic cells have been extensively studied, the ability of other APC types, such as B cells, to induce a CD8(+) T cell response have not been thoroughly evaluated. METHODOLOGY/PRINCIPAL FINDINGS: In this manuscript, we have characterized the ability of CD40-activated B cells, stimulated or not with Toll-like receptor (TLR) agonists (CpG or lipopolysaccharide) to induce the response of mouse naïve CD8(+) T cells in vivo. Our results show that CD40-activated B cells can directly present antigen to naïve CD8(+) T cells to induce the generation of potent effectors able to secrete cytokines, kill target cells and control a Listeria monocytogenes infection. However, CD40-activated B cell immunization did not lead to the proper formation of CD8(+) memory T cells and further maturation of CD40-activated B cells with TLR agonists did not promote the development of CD8(+) memory T cells. Our results also suggest that inefficient generation of CD8(+) memory T cells with CD40-activated B cell immunization is a consequence of reduced Bcl-6 expression by effectors and enhanced contraction of the CD8(+) T cell response. CONCLUSIONS: Understanding why CD40-activated B cell immunization is defective for the generation of memory T cells and gaining new insights about signals that should be provided by APCs are key steps before translating the use of CD40-B cell for therapeutic vaccination.