B and CD4+ T‐cell expression of TLR2 is critical for optimal induction of a T‐cell‐dependent humoral immune response to intact Streptococcus pneumoniae

TLR2^?/? mice immunized with Streptococcus pneumoniae (Pn) elicit normal IgM, but defective CD4⁺ T‐cell‐dependent type 1 IgG isotype production, associated with a largely intact innate immune response. We studied the T‐cell‐dependent phosphorylcholine (PC)‐specific IgG3 versus the T‐cell‐independent IgM response to Pn to determine whether TLR2 signals directly via the adaptive immune system. Pn‐activated TLR2^?/? BMDC have only a modest defect in cytokine secretion, undergo normal maturation, and when transferred into naïve WT mice elicit a normal IgM and IgG3 anti‐PC response, relative to WT BMDC. Pn synergizes with BCR and TCR signaling for DNA synthesis in purified WT B and CD4⁺T cells, respectively, but is defective in cells lacking TLR2. Pn primes TLR2^?/? mice for a normal CD4⁺ T‐cell IFN‐γ recall response. Notably, TLR2^?/? B cells transferred into RAG‐2^?/? mice with WT CD4⁺T cells, or TLR2^?/? CD4⁺T cells transferred into athymic nude mice, each elicit a defective IgG3, in contrast to normal IgM, anti‐PC response relative to WT cells. These data are the first to demonstrate a major role for B‐cell and CD4⁺ T‐cell expression of TLR2 for eliciting an anti‐bacterial humoral immune response.     

Mycobacterium tuberculosis RpfE promotes simultaneous Th1‐ and Th17‐type T‐cell immunity via TLR4‐dependent maturation of dendritic cells

Reciprocal induction of the Th1 and Th17 immune responses is essential for optimal protection against Mycobacterium tuberculosis (Mtb); however, only a few Mtb antigens are known to fulfill this task. A functional role for resuscitation‐promoting factor (Rpf) E, a latency‐associated member of the Rpf family, in promoting naïve CD4⁺ T‐cell differentiation toward both Th1 and Th17 cell fates through interaction with dendritic cells (DCs) was identified in this study. RpfE induces DC maturation by increasing expression of surface molecules and the production of IL‐6, IL‐1β, IL‐23p19, IL‐12p70, and TNF‐α but not IL‐10. This induction is mediated through TLR4 binding and subsequent activation of ERK, p38 MAPKs, and NF‐κB signaling. RpfE‐treated DCs effectively caused naïve CD4⁺ T cells to secrete IFN‐γ, IL‐2, and IL‐17A, which resulted in reciprocal expansions of the Th1 and Th17 cell response along with activation of T‐bet and RORγt but not GATA‐3. Furthermore, lung and spleen cells from Mtb‐infected WT mice but not from TLR4^?/? mice exhibited Th1 and Th17 polarization upon RpfE stimulation. Taken together, our data suggest that RpfE has the potential to be an effective Mtb vaccine because of its ability to activate DCs that simultaneously induce both Th1‐ and Th17‐polarized T‐cell expansion.     

Antigen dose‐dependent suppression of murine IgE responses is mediated by CD4−CD8− double‐negative T cells

Background The IgE response against protein antigens is profoundly influenced by the dose used for sensitization. Objective The aim of the study was to identify immune cells that are involved in antigen dose‐dependent regulation of IgE formation. Methods Wild‐type mice as well as T helper (Th)1‐deficient IL‐12p40^?/? and IFN‐γ^?/? mice were immunized by repeated intraperitoneal injection of either low doses (K01 mice) or high doses (K100 mice) of keyhole limpet haemocyanin adsorbed to aluminium hydroxide. Splenocytes of immunized mice were restimulated in vitro and antigen‐dependent T cell proliferation and cytokine production were measured. The frequency of regulatory T cell subsets among splenocytes from K01 and K100 mice was compared using fluorocytometry and RT‐PCR analysis. Splenocytes or T cell subpopulations were transferred into naïve mice and the effect of lymphocyte transfer on IgE production after priming of recipients with low antigen doses was determined. Results Specific IgE production was considerably impaired in K100 mice. Antigenic restimulation revealed hypoproliferation of K100 splenocytes and reduced production of Th2 cytokines IL‐4, IL‐5 and IL‐13, but no induction of IFN‐γ production. Moreover, lymphocytes from K01 and K100 mice did not show significant differences in the expression of molecules associated with the phenotype or activity of conventional regulatory T cells. Transfer of splenocytes or purified T cells from K100 mice substantially suppressed the induction of IgE production in the recipients in an antigen‐ and isotype‐specific manner. Neither CD4⁺ nor CD8⁺ T cells from K100 mice were able to inhibit IgE formation; instead, we identified CD4^?CD8^? double‐negative T cells (dnT cells) as the principal T cell population, which potently suppressed IgE production. Conclusion Our data demonstrate that CD4^?CD8^? dnT cells play a major role in the regulation of IgE responses induced by high antigen doses.     

Differential requirement for CARMA1 in agonist‐selected T‐cell development

Caspase recruitment domain‐containing membrane‐associated guanylate kinase protein‐1 (CARMA1) is a critical component of the NF‐κB signaling cascade mediated by TCR engagement. In addition to activation of naïve T cells, TCR signaling is important for the development of agonist‐selected T‐cell subsets such as Treg, NKT cells, and CD8‐αα T cells. However, little is known about the role of CARMA1 in the development of these lineages. Here we show that CARMA1‐deficient mice (CARMA1^?/?) have altered populations of specific subsets of agonist‐selected T cells. Specifically, CARMA1^?/? mice have impaired natural and adaptive Treg development, whereas NKT cell numbers are normal compared with wild‐type mice. Interestingly, CD8‐αα T cells, which may also be able to develop through an extrathymic selection pathway, are enriched in the gut of CARMA1^?/? mice, whereas memory‐phenotype CD4⁺ T cells (CD62L^low/CD44^high) are present at reduced numbers in the periphery. These results indicate that CARMA1 is essential for Treg development, but is not necessary for the development of other agonist‐selected T‐cell subsets. Overall, these data reveal an important but differential role for CARMA1‐mediated TCR signaling in T‐cell development.     

Increased numbers of thymic and peripheral CD4+ CD25+Foxp3+ cells in the absence of CD5 signaling

It has been suggested that high affinity/avidity interactions are required for the thymic selection of Treg. Here, we investigated the role of CD5, a negative regulator of TCR signaling, in the selection and function of “naturally occurring” CD4⁺CD25⁺ Treg (nTreg). Analysis of CD5^?/? mice showed a significant increase in the percentage and absolute numbers of CD4⁺ CD25⁺Foxp3⁺ thymocytes and peripheral T lymphocytes, compared with BALB/c mice. Thymi from CD5^?/? mice showed reduced cellularity due to increased apoptosis, which preferentially affected naïve T cells. To characterize nTreg selection at the molecular level we investigated the phosphorylation of Erk, c‐Cbl, PI3K and Akt. CD5^?/? nTreg showed increased basal levels of p‐Erk compared with wild‐type nTreg. Interestingly, in response to CD3 plus CD28 costimulation, CD5^?/? naïve T cells but not CD5^?/? nTreg showed lower levels of p‐Akt. Finally, CD5^?/? nTreg were thymus‐derived and fully functional. We conclude that the enrichment of nTreg observed in the absence of CD5 signaling is due to de novo generation of nTreg and selective reduction of CD4⁺CD25^? naïve thymocytes. Furthermore, we provide new evidence supporting a potential role of CD5 in thymocyte survival, through a mechanism that may involve the phosphorylation of Akt.     

In CD28‐costimulated human naïve CD4+ T cells,I‐κB kinase controls the expression of cell cycle regulatory proteins via interleukin‐2‐independent mechanisms

Stimulation of naïve CD4⁺ T cells through engagement of the T‐cell receptor (TCR) and the CD28 co‐receptor initiates cell proliferation which critically depends on interleukin (IL)‐2 secretion and subsequent autocrine signalling via the IL‐2 receptor. However, several studies indicate that in CD28‐costimulated T cells additional IL‐2‐independent signals are also required for cell proliferation. In this study, using a neutralizing anti‐human IL‐2 antibody and two selective, structurally unrelated, cell‐permeable I‐κB kinase (IKK) inhibitors, BMS‐345541 and PS‐1145, we show that in human naïve CD4⁺ T cells stimulated through a short engagement of the TCR and the CD28 co‐receptor, IKK controls the expression of the cell cycle regulatory proteins cyclin D3, cyclin E and cyclin‐dependent kinase 2 (CDK2) and the stability of the F‐box protein S‐phase kinase‐associated protein 2 (SKP2) and its co‐factor CDC28 protein kinase regulatory subunit 1B (CKS1B), through IL‐2‐independent mechanisms.     

Soluble TNF‐α but not transmembrane TNF‐α sensitizes T cells for enhanced activation‐induced cell death

In addition to its proinflammatory effects, TNF‐α exhibits immunosuppression. Here, we compared the capacities of transmembrane TNF‐α (tmTNF) and soluble TNF‐α (sTNF) in regulating expansion of activated T cells by apoptosis. Splenic CD4⁺ T cells from wtTNF, TNF‐α‐deficient (TNF^?/?) and TNF^?/? mice expressing a non‐cleavable mutant tmTNF showed comparable proliferation rates upon TCR‐mediated stimulation. Activation‐induced cell death (AICD), however, was significantly attenuated in tmTNF and TNF^?/?, compared with wtTNF CD4⁺ T cells. Addition of sTNF during initial priming was sufficient to enhance susceptibility to AICD in tmTNF and TNF^?/? CD4⁺ T cells to levels seen in wtTNF CD4⁺ T cells, whereas addition of sTNF only during restimulation failed to enhance AICD. sTNF‐induced, enhanced susceptibility to AICD was dependent on both TNF receptors. The reduced susceptibility of tmTNF CD4⁺ T cells for AICD was also evident in an in vivo model of adoptively transferred CD4⁺ T‐cell‐mediated colonic inflammation. Hence, the presence of sTNF during T‐cell priming may represent an important mechanism to sensitize activated T cells for apoptosis, thereby attenuating the extent and duration of T‐cell reactivities and subsequent T‐cell‐mediated, excessive inflammation.     

Dendritic cell homeostasis is maintained by nonhematopoietic and T‐cell‐produced Flt3‐ligand in steady state and during immune responses

Lymphoid‐tissue dendritic cells (DCs) are short‐lived and need to be continuously replenished from bone marrow‐derived DC progenitor cells. Fms‐related tyrosine kinase 3 is expressed during cellular development from hematopoietic progenitors to lymphoid‐tissue DCs. Fms‐related tyrosine kinase 3 ligand (Flt3L) is an essential, nonredundant cytokine for DC progenitor to lymphoid tissue DC differentiation and maintenance. However, which cells contribute to Flt3L production and how Flt3L cytokine levels are regulated in steady state and during immune reactions remains to be determined. Here we demonstrate that besides nonhematopoietic cells, WT T cells produce Flt3L and contribute to the generation of both classical DCs (cDCs) and plasmacytoid DCs in Flt3L^?/? mice. Upon stimulation in vitro, CD4⁺ T cells produce more Flt3L than CD8⁺ T cells. Moreover, in vivo stimulation of naïve OT‐II CD4⁺ T cells with OVA leads to increase of pre‐cDCs and cDCs in draining lymph nodes of Flt3L^?/? mice in a partially Flt3L‐dependent manner. Thus, Flt3L‐mediated lymphoid tissue DC homeostasis is regulated by steady‐state T cells as well as by proliferative T cells, fostering local development of lymphoid organ resident DCs.     

Cardiolipin activates antigen‐presenting cells via TLR2‐PI3K‐PKN1‐AKT/p38‐NF‐kB signaling to prime antigen‐specific naïve T cells in mice

Mitochondrial defects and antimitochondrial cardiolipin (CL) antibodies are frequently detected in autoimmune disease patients. CL from dysregulated mitochondria activates various pattern recognition receptors, such as NLRP3. However, the mechanism by which mitochondrial CL activates APCs as a damage‐associated molecular pattern to prime antigen‐specific naïve T cells, which is crucial for T‐cell‐dependent anticardiolipin IgG antibody production in autoimmune diseases is unelucidated. Here, we show that CL increases the expression of costimulatory molecules in CD11c⁺ APCs both in vitro and in vivo. CL activates CD11c⁺ APCs via TLR2‐PI3K‐PKN1‐AKT/p38MAPK‐NF‐κB signaling. CD11c⁺ APCs that have been activated by CL are sufficient to prime H‐Y peptide‐specific naïve CD4⁺ T cells and OVA‐specific naïve CD8⁺ T cells. TLR2 is necessary for anti‐CL IgG antibody responses in vivo. Intraperitoneal injection of CL does not activate CD11c⁺ APCs in CD14 KO mice to the same extent as in wild‐type mice. CL binds to CD14 (Kd = 7 × 10^?7 M). CD14, but not MD2, plays a role in NF‐kB activation by CL, suggesting that CD14⁺ macrophages contribute to recognizing CL. In summary, CL activates signaling pathways in CD11c⁺ APCs through a mechanism similar to gram (+) bacteria and plays a crucial role in priming antigen‐specific naïve T cells.     

Suppressive and pro‐inflammatory roles for IL‐4 in the pathogenesis of experimental drug‐induced liver injury

The pathogenesis of immune‐mediated drug‐induced liver injury (DILI) following halogenated anesthetics, carbamazepine or alcohol has not been fully elucidated. Detecting cytochrome P450 2E1 (CYP2E1) IgG4 auto‐antibodies in anesthetic DILI patients suggests a role for IL‐4 in this hapten‐mediated process. We investigated IL‐4‐mediated mechanisms using our model of experimental DILI induced by immunizing BALB/c (WT) and IL‐4^?/? (KO) mice with S100 liver proteins covalently modified by a trifluoroacetyl chloride (TFA) hapten formed following halogenated anesthetic metabolism by CYP2E1. WT mice developed more hepatitis, TFA and S100 antibodies (p<0.01), as well as T‐cell proliferation to CYP2E1 and TFA (p<0.01) than KO mice. Additionally, WT CD4⁺ T cells adoptively transferred hepatitis to naïve Rag^?/? mice (p<0.01). Pro‐inflammatory cytokines were expectedly decreased in TFA hapten‐stimulated KO splenocyte supernatants (p<0.001); however, IL‐2 and IFN‐γ (p<0.05), as well as IL‐6 and IL‐10 (p<0.001) levels were elevated in CYP2E1‐stimulated KO splenocyte supernatants, suggesting dual IL‐4‐mediated pro‐inflammatory and regulatory responses. Anti‐IL‐10 administered to KO mice increased hepatitis, TFA and CYP2E1 antibodies in KO mice confirming a critical role for IL‐4. This is the first demonstration of dual roles for IL‐4 in the pathogenesis of immune‐mediated DILI by suppressing auto‐antigen‐induced regulatory responses while promoting hapten‐induced pro‐inflammatory responses.     

Gadd45b and Gadd45g are important for anti‐tumor immune responses

An effective Th1 type cell‐mediated immune response against cancer cells is critical in limiting cancer progression. Gadd45b, a signaling molecule highly up‐regulated during Th1 type responses, is studied for its role in limiting tumor growth. Mouse B16 melanoma cells implanted into Gadd45b^?/? mice grew faster than those in WT or Gadd45b^+/? littermate controls. The defect of Gadd45b^?/? mice in tumor immunosurveillance was attributed to the reduced expression of IFN‐γ, granzyme B, and CCR5 in Gadd45b^?/? CD8⁺ T cells at the tumor site. Activation of p38 MAP kinase, but not ERK or JNK, by either TCR‐stimuli or IL‐12 and IL‐18 is diminished in Gadd45b^?/? CD8⁺ T cells, resulting in reduced production of IFN‐γ. In addition, mRNA of T‐bet and Eomes were reduced in Gadd45b^?/? CD8⁺ T cells, supporting a critical role of Gadd45b in shaping the Th1 fate. More importantly, the tumor vaccination, which is effective in WT mice, failed in Gadd45b/Gadd45g doubly deficient mice. Collectively, these data demonstrate that members of the Gadd45 gene family are important for anti‐tumor immune responses.     

Interleukin-33 amplifies IgE synthesis and triggers mast cell degranulation via interleukin-4 in naïve mice

Background

The regulation and function of IgE in healthy individuals and in antigen‐naïve animals is not well understood. IL‐33 administration increases serum IgE in mice with unknown mechanism. We tested the hypothesis that IL‐33 provides an antigen‐independent stimulus for IgE production and mast cell degranulation.

Methods

IL‐33 was administered to naïve wild‐type (WT), nude and ST2^?/?, IL‐4^?/?, IL4Rα^?/? and T‐or B‐cell‐specific IL‐4Rα^?/? mice. IgEand cytokines were quantified by ELISA. T‐ and B‐lymphocyte numbers and CD40L expression were determined by flow cytometry. Anaphylaxis was measured by temperature, mast cell degranulation and histamine release.

Results

IL‐33 enhanced IgE production in naïve WT, T‐IL‐4Rα^?/? but not in ST2^?/?, IL‐4^?/?, IL‐4Rα^?/? or B‐cell‐specific IL‐4Rα^?/? mice, demonstrating IL‐33 specificity and IL‐4 dependency. Moreover, IL‐4 was required for IL‐33‐induced B‐cell proliferation and T‐cell CD40L expression, which promotes IgE production. IL‐33‐induced IL‐4 production was mainly from innate cells including mast cells and eosinophils. IL‐33 increased mast cell surface IgE and triggered degranulation and systemic anaphylaxis in allergen‐naïve WT but not in IL‐4Rα^?/? mice.

Conclusion

IL‐33 amplifies IgE synthesis and triggers anaphylaxis in naïve mice via IL‐4, independent of allergen. IL‐33 may play an important role in nonatopic allergy and idiopathic anaphylaxis.

     

IL‐15 is critical for the maintenance and innate functions of self‐specific CD8+ T cells

IL‐15 is a pleiotropic cytokine involved in host defense as well as autoimmunity. IL‐15‐deficient mice show a decrease of memory phenotype (MP) CD8⁺ T cells, which develop naturally in naïve mice and whose origin is unclear. It has been shown that self‐specific CD8⁺ T cells developed in male H‐Y antigen‐specific TCR transgenic mice share many similarities with naturally occurring MP CD8⁺ T cells in normal mice. In this study, we found that H‐Y antigen‐specific CD8⁺ T cells in male but not female mice decreased when they were crossed with IL‐15‐deficient mice, mainly due to impaired peripheral maintenance. The self‐specific TCR transgenic CD8⁺ T cells developed in IL‐15‐deficient mice showed altered surface phenotypes and reduced effector functions ex vivo. Bystander activation of the self‐specific CD8⁺ T cells was induced in vivo during infection with Listeria monocytogenes, in which proliferation but not IFN‐γ production was IL‐15‐dependent. These results indicated important roles for IL‐15 in the maintenance and functions of self‐specific CD8⁺ T cells, which may be included in the naturally occurring MP CD8⁺ T‐cell population in naïve normal mice and participate in innate host defense responses.     

T‐cell tolerance induced by repeated antigen stimulation: Selective loss of Foxp3− conventional CD4 T cells and induction of CD4 T‐cell anergy

Repeated immunization of mice with bacterial superantigens induces extensive deletion and anergy of reactive CD4 T cells. Here we report that the in vitro proliferation anergy of CD4 T cells from TCR transgenic mice immunized three times with staphylococcal enterotoxin B (SEB) (3× SEB) is partially due to an increased frequency of Foxp3⁺ CD4 T cells. Importantly, reduced number of conventional CD25^? Foxp3^? cells, rather than conversion of such cells to Foxp3⁺ cells, was the cause of that increase and was also seen in mice repeatedly immunized with OVA (3× OVA) and OVA—peptide (OVAp) (3× OVAp). Cell‐transfer experiments revealed profound but transient anergy of CD4 T cells isolated from 3× OVAp and 3× SEB mice. However, the in vivo anergy was CD4 T‐cell autonomous and independent of Foxp3⁺ Treg. Finally, proliferation of transferred CD4 T cells was inhibited in repeatedly immunized mice but inhibition was lost when transfer was delayed, despite the maintenance of elevated frequency of Foxp3⁺ cells. These data provide important implications for Foxp3⁺ cell‐mediated tolerance in situations of repeated antigen exposure such as human persistent infections.     

Toll‐like receptor 2 agonist Pam3CSK4 enhances the induction of antigen‐specific tolerance via the sublingual route

Background Sublingual immunotherapy (SLIT) has been established in humans as a safe and efficacious treatment for type I respiratory allergies. Objective In this study, we compared three Toll‐like receptor (TLR) 2 ligands (Pam3CSK4, Porphyromonas gingivalis lipopolysaccharide and lipoteichoic acid) as potential adjuvants for sublingual allergy vaccines. Methods These molecules were tested in co‐cultures of adjuvant‐pre‐treated dendritic cells (DCs) with murine naïve CD4⁺ T lymphocytes. Patterns of cytokine production, phenotype, proliferation and gene expression were analysed by ELISA, cytofluorometry and quantitative PCR, respectively. TLR2 ligands were subsequently tested in a model of SLIT in BALB/c mice sensitized with ovalbumin (OVA). Results Among the three TLR2 ligands tested, the synthetic lipopeptide Pam3CSK4 is the most potent inducer of IL‐12p35 and IL‐10 gene expression in murine bone marrow‐derived DCs, as well as in purified oral myeloid DCs. Only Pam3CSK4‐treated DCs induce IFN‐γ and IL‐10 secretion by naïve CD4⁺ T cells. Sublingual administration of Pam3CSK4 together with the antigen in BALB/c mice sensitized to OVA decreases airway hyperresponsiveness as well as OVA‐specific T‐helper type 2 (Th2) responses in cervical lymph nodes dramatically. Conclusion Pam3CSK4 induces Th1/regulatory T cell responses, and as such, is a valid candidate adjuvant for sublingual allergy vaccines.     

Differential requirements of CD4+ T‐cell signals for effector cytotoxic T‐lymphocyte (CTL) priming and functional memory CTL development at higher CD8+ T‐cell precursor frequency

Increased CD8⁺ T‐cell precursor frequency (PF) precludes the requirement of CD4⁺ helper T (Th) cells for primary CD8⁺ cytotoxic T‐lymphocyte (CTL) responses. However, the key questions of whether unhelped CTLs generated at higher PF are functional effectors, and whether unhelped CTLs can differentiate into functional memory cells at higher PF are unclear. In this study, ovalbumin (OVA) ‐pulsed dendritic cells (DC_OVA) derived from C57BL/6, CD40 knockout (CD40^?/?) or CD40 ligand knockout (CD40L^?/?) mice were used to immunize C57BL/6, Ia^b?/?, CD40^?/? or CD40L^?/? mice, whose PF was previously increased with transfer of 1 × 10⁶ CD8⁺ T cells derived from OVA‐specific T‐cell receptor (TCR) transgenic OTI, OTI(CD40^?/?) or OTI(CD40L^?/?) mice. All the immunized mice were then assessed for effector and memory CTL responses. Following DC immunization, relatively comparable CTL priming occurred without CD4⁺ T‐cell help and Th‐provided CD40/CD40L signalling. In addition, the unhelped CTLs were functional effectors capable of inducing therapeutic immunity against established OVA‐expressing tumours. In contrast, the functional memory development of CTLs was severely impaired in the absence of CD4⁺ T‐cell help and CD40/CD40L signalling. Finally, unhelped memory CTLs failed to protect mice against lethal tumour challenge. Taken together, these results demonstrate that CD4⁺ T‐cell help at higher PF, is not required for effector CTL priming, but is required for functional memory CTL development against cancer. Our data may impact the development of novel preventive and therapeutic approaches in cancer patients with compromised CD4⁺ T‐cell functions.     

IFN‐γ‐producing NKT cells exacerbate sepsis by enhancing C5a generation via IL‐10‐mediated inhibition of CD55 expression on neutrophils

A role for NKT cells has been implicated in sepsis, but the mechanism by which NKT cells contribute to sepsis remains unclear. Here, we examined WT and NKT‐cell‐deficient mice of C57BL/6 background during cecal ligation and puncture‐induced sepsis. The levels of C5a, IFN‐γ, and IL‐10 were higher in the serum and peritoneal fluid of WT mice than in those of CD1d^?/? mice, while the mortality rate was lower in CD1d^?/? mice than in WT mice. C5a blockade decreased mortality of WT mice during sepsis, whereas it did not alter that of CD1d^?/? mice. As assessed by intracellular staining, NKT cells expressed IFN‐γ, while neutrophils expressed IL‐10. Upon coculture, IL‐10‐deficient NKT cells enhanced IL‐10 production by WT, but not IFN‐γR‐deficient, neutrophils. Meanwhile, CD1d^?/? mice exhibited high CD55 expression on neutrophils during sepsis, whereas those cells from WT mice expressed minimal levels of CD55. Recombinant IL‐10 administration into CD1d^?/? mice reduced CD55 expression on neutrophils. Furthermore, adoptive transfer of sorted WT, but not IFN‐γ‐deficient, NKT cells into CD1d^?/? mice suppressed CD55 expression on neutrophils, but increased IL‐10 and C5a levels. Taken together, IFN‐γ‐producing NKT cells enhance C5a generation via IL‐10‐mediated inhibition of CD55 expression on neutrophils, thereby exacerbating sepsis.     

Interrupting CD28 costimulation before antigen rechallenge affects CD8+ T‐cell expansion and effector functions during secondary response in mice

The role of CD28‐mediated costimulation in secondary CD8⁺ T‐cell responses remains controversial. Here, we have used two tools — blocking mouse anti‐mouse CD28‐specific antibodies and inducible CD28‐deleting mice — to obtain definitive answers in mice infected with ovalbumin‐secreting Listeria monocytogenes. We report that both blockade and global deletion of CD28 reveal its requirement for full clonal expansion and effector functions such as degranulation and IFN‐γ production during the secondary immune response. In contrast, cell‐intrinsic deletion of CD28 in transferred TCR‐transgenic CD8⁺ T cells before primary infection leads to impaired clonal expansion but an increase in cells able to express effector functions in both primary and secondary responses. We suggest that the proliferation‐impaired CD8⁺ T cells respond to CD28‐dependent help from their environment by enhanced functional differentiation. Finally, we report that cell‐intrinsic deletion of CD28 after the peak of the primary response does not affect the establishment, maintenance, or recall of long‐term memory. Thus, if given sufficient time, the progeny of primed CD8⁺ T cells adapt to the absence of this costimulator.     

Suppression of antigen-specific CD4<Superscript>+</Superscript> T cell activation by SRA/CD204 through reducing the immunostimulatory capability of antigen-presenting cell

Pattern recognition scavenger receptor SRA/CD204, primarily expressed on specialized antigen-presenting cells (APCs), including dendritic cells (DCs) and macrophages, has been implicated in multiple physiological and pathological processes, including atherosclerosis, Alzheimer’s disease, endotoxic shock, host defense, and cancer development. SRA/CD204 was also recently shown to function as an attenuator of vaccine response and antitumor immunity. Here, we, for the first time, report that SRA/CD204 knockout (SRA^?/?) mice developed a more robust CD4⁺ T cell response than wild-type mice after ovalbumin immunization. Splenic DCs from the immunized SRA^?/? mice were much more efficient than those from WT mice in stimulating naïve OT-II cells, indicating that the suppressive activity of SRA/CD204 is mediated by DCs. Strikingly, antigen-exposed SRA^?/? DCs with or without lipopolysaccharide treatment exhibited increased T-cell-stimulating activity in vitro, which was independent of the classical endocytic property of the SRA/CD204. Additionally, absence of SRA/CD204 resulted in significantly elevated IL12p35 expression in DCs upon CD40 ligation plus interferon gamma (IFN-γ) stimulation. Molecular studies reveal that SRA/CD204 inhibited the activation of STAT1, mitogen activated protein kinase p38, and nuclear factor-kappa B signaling activation in DCs treated with anti-CD40 antibodies and IFN-γ. Furthermore, splenocytes from the generated SRA^?/? OT-II mice showed heightened proliferation upon stimulation with OVA protein or MHC-II-restricted OVA_323–339 peptide compared with cells from the SRA^+/+ OT-II mice. These results not only establish a new role of SRA/CD204 in limiting the intrinsic immunogenicity of APCs and CD4⁺ T cell activation but also provide additional insights into the molecular mechanisms involved in the immune suppression by this molecule.