An IFN-γ-IL-18 signaling loop accelerates memory CD8+ T cell proliferation

Rapid proliferation is one of the important features of memory CD8+ T cells, ensuring rapid clearance of reinfection. Although several cytokines such as IL-15 and IL-7 regulate relatively slow homeostatic proliferation of memory T cells during the maintenance phase, it is unknown how memory T cells can proliferate more quickly than naïve T cells upon antigen stimulation. To examine antigen-specific CD8+ T cell proliferation in recall responses in vivo, we targeted a model antigen, ovalbumin(OVA), to DEC-205+ dendritic cells (DCs) with a CD40 maturation stimulus. This led to the induction of functional memory CD8+ T cells, which showed rapid proliferation and multiple cytokine production (IFN-γ, IL-2, TNF-α) during the secondary challenge to DC-targeted antigen. Upon antigen-presentation, IL-18, an IFN-γ-inducing factor, accumulated at the DC:T cell synapse. Surprisingly, IFN-γ receptors were required to augment IL-18 production from DCs. Mice genetically deficient for IL-18 or IFN-γ-receptor 1 also showed delayed expansion of memory CD8+ T cells in vivo. These results indicate that a positive regulatory loop involving IFN-γ and IL-18 signaling contributes to the accelerated memory CD8+ T cell proliferation during a recall response to antigen presented by DCs

Targeting Leishmania major Antigens to Dendritic Cells In Vivo Induces Protective Immunity

Efficient vaccination against the parasite Leishmania major, the causative agent of human cutaneous leishmaniasis, requires development of type 1 T-helper (Th1) CD4+ T cell immunity. Because of their unique capacity to initiate and modulate immune responses, dendritic cells (DCs) are attractive targets for development of novel vaccines. In this study, for the first time, we investigated the capacity of a DC-targeted vaccine to induce protective responses against L. major. To this end, we genetically engineered the N-terminal portion of the stress-inducible 1 protein of L. major (LmSTI1a) into anti-DEC205/CD205 (DEC) monoclonal antibody (mAb) and thereby delivered the conjugated protein to DEC+ DCs in situ in the intact animal. Delivery of LmSTI1a to adjuvant-matured DCs increased the frequency of antigen-specific CD4+ T cells producing IFN-γ+, IL-2+, and TNF-α+ in two different strains of mice (C57BL/6 and Balb/c), while such responses were not observed with the same doses of a control Ig-LmSTI1a mAb without receptor affinity or with non-targeted LmSTI1a protein. Using a peptide library for LmSTI1a, we identified at least two distinct CD4+ T cell mimetopes in each MHC class II haplotype, consistent with the induction of broad immunity. When we compared T cell immune responses generated after targeting DCs with LmSTI1a or other L. major antigens, including LACK (Leishmania receptor for activated C kinase) and LeIF (Leishmania eukaryotic ribosomal elongation and initiation factor 4a), we found that LmSTI1a was superior for generation of IFN-γ-producing CD4+ T cells, which correlated with higher protection of susceptible Balb/c mice to a challenge with L. major. For the first time, this study demonstrates the potential of a DC-targeted vaccine as a novel approach for cutaneous leishmaniasis, an increasing public health concern that has no currently available effective treatment

A subset of dendritic cells induces CD4+ T cells to produce IFN-γ by an IL-12–independent but CD70-dependent mechanism in vivo

Interferon (IFN)-γ, a cytokine critical for resistance to infection and tumors, is produced by CD4+ helper T lymphocytes after stimulation by cultured dendritic cells (DCs) that secrete a cofactor, interleukin (IL)-12. We have identified a major IL-12–independent pathway whereby DCs induce IFN-γ–secreting T helper (Th)1 CD4+ T cells in vivo. This pathway requires the membrane-associated tumor necrosis family member CD70 and was identified by targeting the LACK antigen from Leishmania major within an antibody to CD205 (DEC-205), an uptake receptor on a subset of DCs. Another major DC subset, targeted with 33D1 anti-DCIR2 antibody, also induced IFN-γ in vivo but required IL-12, not CD70. Isolated CD205+ DCs expressed cell surface CD70 when presenting antigen to T cell receptor transgenic T cells, and this distinction was independent of maturation stimuli. CD70 was also essential for CD205+ DC function in vivo. Detection of the IL-12–independent IFN-γ pathway was obscured with nontargeted LACK, which was presented by both DC subsets. This in situ analysis points to CD70 as a decision maker for Th1 differentiation by CD205+ DCs, even in Th2-prone BALB/c animals and potentially in vaccine design. The results indicate that two DC subsets have innate propensities to differentially affect the Th1/Th2 balance in vivo and by distinct mechanisms

Two Novel Variants of the v-srcOncogene Isolated from Low and High Metastatic RSV-Transformed Hamster Cells

AbstractFour different transformed cell lines were isolated as a result of independent infection of primary hamster fibroblasts by Rous sarcoma virus (RSV SR-D stocks). These lines differ by the level of their spontaneous metastatic activity: HET-SR-1, HET-SR-8, and HET-SR-10 cell lines induced 70–200 metastatic nodules in the lung and/or lymph nodes of inoculated animals (high metastatic lines, HM). Metastatic activity was not identified after injection of HET-SR cells (low metastatic line, LM). All cell lines contained one copy of integrated and expressed intact RSV provirus. The difference in the amount of v-srcprotein in cell lines was not correlated with their metastatic potentialin vivo.Complete v-srcHM and v-srcLM genes were cloned from corresponding gene libraries and sequenced. In the unique region of both v-srcisoforms a GC-rich insert of 60 nucleotides (20 a.a.) was found. The presence of this insert explains the unusual apparent molecular weight of protein encoded by v-srcHM and v-srcLM: 62 kDa. Both genes had 10 identical amino acid changes when compared to the known RSV SR-D v-srcsequence. v-srcHM and v-srcLM differ by several amino acid changes. Most of them are localized in the unique domain and the extreme carboxy-terminal region of the oncoprotein. Both v-srcvariants and chimeric v-srcwith mutually substituted parts were subcloned in a retroviral vector and introduced into avian neuroretina cells. Significant differences in the morphology of transformed neuroretina cells were associated with the mutations in the carboxy-terminal region of the v-srconcogene. Low metastatic HET-SR cells transfected with v-srcHM and the chimeric gene v-src-LH remarkably increased their metastatic potential. In contrast, this effect was not observed when the same cells were transfected with v-srcLM and the chimeric v-srcHL gene. Specific changes in the distribution of fibronectin matrix typical for high metastatic cells were found in the lines transfected with v-srcHM

An IFN-γ-IL-18 Signaling Loop Accelerates Memory CD8+ T Cell Proliferation

Rapid proliferation is one of the important features of memory CD8+ T cells, ensuring rapid clearance of reinfection. Although several cytokines such as IL-15 and IL-7 regulate relatively slow homeostatic proliferation of memory T cells during the maintenance phase, it is unknown how memory T cells can proliferate more quickly than naïve T cells upon antigen stimulation. To examine antigen-specific CD8+ T cell proliferation in recall responses in vivo, we targeted a model antigen, ovalbumin(OVA), to DEC-205+ dendritic cells (DCs) with a CD40 maturation stimulus. This led to the induction of functional memory CD8+ T cells, which showed rapid proliferation and multiple cytokine production (IFN-γ, IL-2, TNF-α) during the secondary challenge to DC-targeted antigen. Upon antigen-presentation, IL-18, an IFN-γ-inducing factor, accumulated at the DC:T cell synapse. Surprisingly, IFN-γ receptors were required to augment IL-18 production from DCs. Mice genetically deficient for IL-18 or IFN-γ-receptor 1 also showed delayed expansion of memory CD8+ T cells in vivo. These results indicate that a positive regulatory loop involving IFN-γ and IL-18 signaling contributes to the accelerated memory CD8+ T cell proliferation during a recall response to antigen presented by DCs

Analysis of the cytokine responses after challenge with <i>L. major</i>.

<p>As in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0067453#pone-0067453-g005" target="_blank">Figure 5</a>, but 12 weeks after infection with <i>L. major</i>, total cell suspensions of ear-infected draining LN were restimulated <i>in vitro</i> for 72 h with 10 µg/ml of SLA. The levels of IFN-γ, IL-4, and IL-10 cytokines in the culture supernatants were determined by ELISA. Data is shown as the mean ± SEM of the ratio of (A) IFN-γ/IL-4 and (B) IL-10 (n = 4–10).</p