Protease-Activated Receptor 2 Agonist as Adjuvant: Augmenting Development of Protective Memory CD8 T Cell Responses Induced by Influenza Virosomes.

Protease-activated receptor 2 (PAR-2) is expressed in various tissues, including lung, and when activated, promotes inflammation, differentiation, and migration of dendritic cells. We found that combining influenza virosomes containing hemagglutinin and neuraminidase with a PAR-2 agonist peptide (PAR-2AP) in an intranasal prime boost approach increased survival of mice challenged weeks later with lethal influenza virus over that by virosome or PAR-2AP prime boost alone. No weight loss occurred from influenza challenge after virosome-plus-PAR-2AP prime boost compared with either virosomes or PAR-2AP alone. Thus, virosomes plus PAR-2AP prevented morbidity as well as mortality. Through adoptive transfer, CD8+ lung T cells but not CD4+ T cells from virosomes plus PAR-2AP-primed mice protected from lethal influenza virus challenge and enhanced survival with less weight loss and faster recovery. Virosome-plus-PAR-2AP prime boost resulted in greater percentages of T effector memory phenotype cells (Tem) in lung, and higher frequencies of CD8 Tem and T central memory cells displayed effector functions in response to virus challenge in vivo. Virosome-plus-PAR-2AP prime boost also resulted in greater percentages of Ag-specific CD8+ T cells, both Tem and T central memory cells, in lungs of animals subsequently challenged with live influenza virus. Our findings indicate that PAR-2AP, a short peptide, may be a new and useful mucosal adjuvant.

NK cells exacerbate the pathology of influenza virus infection in mice.

NK cells offer a first line of defense against viruses and are considered beneficial to the host during infection. Nevertheless, little is understood regarding the phenotype and function of NK cells in the lung during influenza virus infection. We found that the frequency of NK cells in mouse lung increased during influenza infection, with the majority of a mature phenotype. Cell surface CD107a and intracellular IFN-γ were detected in cells expressing multiple NK-cell receptors in infected lung, suggesting that NK cells were activated during infection. The activating receptor NKp46 was predominantly negative on such cells, possibly as a result of encountering influenza HA. Depletion of NK cells in vivo with anti-asialo GM1 or anti-NK1.1 reduced mortality from influenza infection and surviving mice recovered their body weight. Pathology induced by NK cells was only observed with high, not medium or low-dose influenza infection, indicating that the severity of infection influences NK-cell-mediated pathology. Furthermore, adoptive transfer of NK cells from influenza-infected lung, but not uninfected lung, resulted in more rapid weight loss and increased mortality of influenza-infected mice. Our results indicate that during severe influenza infection of the lung, NK cells have a deleterious impact on the host, promoting mortality.

The activating Ly49W and inhibitory Ly49G NK cell receptors display similar affinities for identical MHC class I ligands.

The Ly49 receptor family plays an important role in the regulation of murine natural killer (NK) cell effector function. They recognize cell surface-expressed class I MHC (MHC-I) and are functionally equivalent to the killer Ig-related receptors (KIRs) in human NK cells. Ly49s exist in activating and inhibitory forms with highly homologous extracellular domains, displaying greater variability in the stalk regions. Inhibitory Ly49s can recognize self-MHC-I and therefore mediate tolerance to self. The role of activating Ly49 receptors is less clear. Some activating Ly49 receptors have been shown to recognize MHC-I molecules. The binding affinity of activating Ly49 receptors with MHC-I is currently unknown, and we sought to examine the affinities of two highly related receptors, an activating and an inhibitory Ly49 receptor, for their shared MHC-I ligands. The ectodomain of inhibitory Ly49G of the BALB/c mouse strain is highly similar to the Ly49W activating receptor in the nonobese diabetic (NOD) mouse. Recombinant soluble Ly49G and W were expressed, refolded, and analyzed for binding affinity with MHC-I by surface plasmon resonance. We found that Ly49G and Ly49W bound with similar affinity to the same MHC-I molecules. These results are a first determination of an activating Ly49 receptor affinity for MHC-I and show that, unlike prior results obtained with activating and inhibitory KIR receptors, functional homologues to Ly49 receptors, activating and inhibitory Ly49, can recognize common MHC-I ligands, with similar affinities.

Seasonal H1N1 influenza virus infection induces cross-protective pandemic H1N1 virus immunity through a CD8-independent, B cell-dependent mechanism.

During the 2009 H1N1 influenza virus pandemic (pdmH1N1) outbreak, it was found that most individuals lacked antibodies against the new pdmH1N1 virus, and only the elderly showed anti-hemagglutinin (anti-HA) antibodies that were cross-reactive with the new strains. Different studies have demonstrated that prior contact with the virus can confer protection against strains with some degree of dissimilarity; however, this has not been sufficiently explored within the context of a pdmH1N1 virus infection. In this study, we have found that a first infection with the A/Brisbane/59/2007 virus strain confers heterologous protection in ferrets and mice against a subsequent pdmH1N1 (A/Mexico/4108/2009) virus infection through a cross-reactive but non-neutralizing antibody mechanism. Heterologous immunity is abrogated in B cell-deficient mice but maintained in CD8(-/-) and perforin-1(-/-) mice. We identified cross-reactive antibodies from A/Brisbane/59/2007 sera that recognize non-HA epitopes in pdmH1N1 virus. Passive serum transfer showed that cross-reactive sH1N1-induced antibodies conferred protection in naive recipient mice during pdmH1N1 virus challenge. The presence or absence of anti-HA antibodies, therefore, is not the sole indicator of the effectiveness of protective cross-reactive antibody immunity. Measurement of additional antibody repertoires targeting the non-HA antigens of influenza virus should be taken into consideration in assessing protection and immunization strategies. We propose that preexisting cross-protective non-HA antibody immunity may have had an overall protective effect during the 2009 pdmH1N1 outbreak, thereby reducing disease severity in human infections.

Recognition of class I MHC by a rat Ly49 NK cell receptor is dependent on the identity of the P2 anchor amino acid of bound peptide.

Members of the rodent Ly49 receptor family control NK cell responsiveness and demonstrate allele specificity for MHC class I (MHC-I) ligands. For example, the rat Ly49i2 inhibitory NK cell receptor binds RT1-A1(c) but not other rat MHC class Ia or Ib molecules. RT1-A1(c) preferentially binds peptides with proline at the second, or P2, position, which defines it as an HLA-B7 supertype MHC-I molecule. Previously, our laboratory showed that mutations within the MHC-I supertype-defining B-pocket of RT1-A1(c) could lead to alterations in P2 anchor residues of the peptide repertoire bound by RT1-A1(c) and loss of recognition by Ly49i2. Although suggestive of peptide involvement, it was unclear whether the peptide P2 anchor residue or alteration of the RT1-A1(c) primary sequence influenced Ly49i2 recognition. Therefore, we directly investigated the role of the P2 anchor residue of RT1-A1(c)-bound peptides in Ly49i2 recognition. First, fluorescent multimers generated by refolding soluble recombinant RT1-A1(c) with individual synthetic peptides differing only at the P2 anchor residue were examined for binding to Ly49i2 NK cell transfectants. Second, cytotoxicity by Ly49i2-expressing NK cells toward RMA-S target cells expressing RT1-A1(c) bound with peptides that only differ at the P2 anchor residue was evaluated. Our results demonstrate that Ly49i2 recognizes RT1-A1(c) bound with peptides that have Pro or Val at P2, whereas little or no recognition is observed when RT1-A1(c) is complexed with peptide bearing Gln at P2. Thus, the identity of the P2 peptide anchor residue is an integral component of MHC-I recognition by Ly49i2.

TCR complex-activated CD8 adhesion function by human T cells.

The CD8 receptor plays a central role in the recognition and elimination of virally infected and malignant cells by cytolytic CD8(+) T cells. In conjunction with the TCR, the CD8 coreceptor binds Ag-specific class I MHC (MHC-I) molecules expressed by target cells, initiating signaling events that result in T cell activation. Whether CD8 can further function as an adhesion molecule for non-Ag MHC-I is currently unclear in humans. In this study, we show that in human CD8(+) T cells, TCR complex signaling activates CD8 adhesion molecule function, resulting in a CD8 interaction with MHC-I that is sufficient to maintain firm T cell adhesion under shear conditions. Secondly, we found that while CD8 adhesive function was triggered by TCR complex activation in differentiated cells, including in vitro generated CTL and ex vivo effector/memory phenotype CD8(+) T cells, naive CD8(+) T cells were incapable of activated CD8 adhesion. Lastly, we examine the kinetics of, and signaling for, activated CD8 adhesion in humans and identify notable differences from the equivalent CD8 function in mouse. Activated CD8 adhesion induced by TCR signaling may contribute to the more rapid and robust elimination of pathogen-infected cells by differentiated CD8(+) T cells.

Vesicle-associated membrane protein 7 (VAMP-7) is essential for target cell killing in a natural killer cell line.

Natural killer cells recognize and induce apoptosis in foreign, transformed or virus-infected cells through the release of perforin and granzymes from secretory lysosomes. Clinically, NK-cell mediated killing is a major limitation to successful allo- and xenotransplantation. The molecular mechanisms that regulate the fusion of granzyme B-containing secretory lysosomes to the plasma membrane in activated NK cells, prior to target cell killing, are not fully understood. Using the NK cell line YT-Indy as a model, we have investigated the expression of SNAP REceptors (SNAREs), both target (t-) and vesicular (v-) SNAREs, and their function in granzyme B-mediated target cell killing. Our data showed that YT-Indy cells express VAMP-7 and SNAP-23, but not VAMP-2. VAMP-7 was associated with granzyme B-containing lysosomal granules. Using VAMP-7 small interfering RNA (siRNA), we successfully knocked down the expression of VAMP-7 protein in YT-Indy to less than 10% of untreated cells in 24h. VAMP7-deficient YT-Indy cells activated via co-culture with Jurkat cells released <1ng/mL of granzyme B, compared to 1.5-2.5 microg/mL from controls. Using Jurkat cells as targets, we showed a 7-fold reduction in NK cell-mediated killing by VAMP-7 deficient YT-Indy cells. Our results show that VAMP-7 is a crucial component of granzyme B release and target cell killing in the NK cell line YT-Indy. Thus, targeting VAMP-7 expression specifically with siRNA, following transplantation, may be a viable strategy for preventing NK cell-mediated transplant rejection, in vivo.

Listeria monocytogenes infection enhances the interaction between rat non-classical MHC-Ib molecule and Ly49 receptors.

Murine NK cell Ly49 receptors, functionally analogous to KIRs in humans recognize MHC class I molecules and play a key role in controlling NK cell function. We have previously shown that the paired activating Ly49s4 and inhibitory Ly49i4 receptors recognize undefined non-classical MHC-Ib ligands from the RT1-CE region in rats. Here, the RT1-CE16 gene of the RT1d haplotype was stably transfected into the mouse RAW macrophage cell line, termed RAW-CE16d cells. Combining RAW-CE16d cells with Ly49 expressing reporter cells demonstrated Ly49i4 and Ly49s4 specificity for CE16d. The Ly49s4/i4:CE16d interaction was confirmed by specific MHC-I blocking monoclonal Abs. Further, we used our in vitro model to study the effect of Listeria monocytogenes (LM) on CE16d after infection. LM infection and IFN-γ stimulation both led to enhanced CE16d expression on the surface of transfected RAW-CE16d cells. Interestingly, the reporter cells displayed increased response to LM-infected RAW-CE16d cells compared with IFN-γ-treated RAW-CE16d cells, suggesting a fundamental difference between these stimuli in supporting enhanced Ly49 recognition of CE16d. Collectively, our data show that Ly49s4 and Ly49i4 recognize the non-classical RT1-CE16d molecule, which in turn is up-regulated during LM infection and thereby may contribute to NK-mediated responses against infected cells.

Listeria monocytogenes infection differentially affects expression of ligands for NK cells and NK cell responses, depending on the cell type infected.

The pivotal role of NK cells in viral infection is extensively studied, whereas the role of NK cells in bacterial infection has been poorly investigated. Here, we have examined how Listeria monocytogenes (LM) affects expression of ligands for NK cell receptors and subsequent NK cell responses, depending on the type of cell infected. LM infected rat cell lines derived from different tissues were coincubated with splenic NK cells, and NK cell proliferation and IFN-γ production were measured. In addition, expression of ligands for the NK cell receptors Ly49 and NK cell receptor protein 1 (NKR-P1), MHC class I and C-type lectin-related molecules, respectively, was assessed. Infected pleural R2 cells, but not epithelium-derived colon carcinoma cell line CC531 cells, induced proliferation of NK cells. Reporter cells expressing the inhibitory NKR-P1G receptor or the activating NKR-P1F receptor were less stimulated under incubation with infected CC531 cells versus uninfected CC531 controls, suggesting that the ligand(s) in question were down-regulated by infection. Conversely, LM infection of R2 cells did not affect reporter cell stimulation compared with uninfected R2 controls. We characterized a rat monocyte cell line, termed RmW cells. In contrast to LM infected R2 cells that up-regulate MHC class I molecules, RmW cells displayed unchanged MHC class I expression following infection. In line with MHC class I expression, more NK cells produced a higher amount of IFN-γ against infected R2 cells compared with RmW cells. Together, L. monocytogenes infection may variously regulate cellular ligands for NK cells, depending on the cell type infected, affecting the outcome of NK cell responses.

Direct detection of cytolytic T lymphocyte-mediated cytotoxicity on antigen-transfected cell microarray.

CD8(+) T lymphocytes are capable of recognizing and destroying cancer cells or virally infected cells and can thus offer protection from cellular malignant transformation and pathogenic challenges. With large numbers of genes discovered in genome analyses, rapid identification of cancer or viral antigens would facilitate better exploitation of CD8(+) T lymphocyte-mediated immune protection. Reverse transfection microarray technology allows expression of individual cDNAs at defined positions in a cell monolayer and direct detection of corresponding phenotypic changes of transfected cells at specific locations. In this study, we have integrated reverse transfection with image-based fluorometric detection of antigen-specific CTL-mediated cytotoxicity on transfected cell microarrays. As a result, the antigen recognition of cloned CTL cells has been successfully detected on the cell microarray, in which the specific or non-specific mini-gene DNA in the expression vector or vector alone was spotted. Moreover, the cellular capability of antigen processing and presentation on microarray has also been evaluated by using chimeric DNA constructs containing the antigen-encoding mini-gene sequence. This novel approach may facilitate high throughput screens of cancer cell or virus cDNA libraries to identify individual cDNAs that encode targets for immune intervention.

Evaluating antigen-specific cytotoxic T lymphocyte responses by a novel mouse granzyme B ELISPOT assay.

We have established novel ELISA- and ELISPOT-based assays specific for the detection of a potent cytotoxic mediator, granzyme B (GrB), for the assessment of antigen-specific cytotoxic T lymphocyte responses in mice. The sensitivity and specificity of our assays was demonstrated by ELISA using purified mouse GrB and supernatants and cell lysates of cytotoxic lymphocytes derived from GrB-deficient mice. No reactivity was observed by the GrB ELISA in GrB-deficient cells. The mouse GrB ELISPOT was successfully employed to detect antigen-specific effector cell responses of two CTL clones, producing GrB ELISPOT results that correlated strongly with target cell lysis, as assessed by 51Cr-release. Furthermore, we were able to demonstrate direct correlations between GrB ELISPOT and killing by LCMV gp33-specific effector and memory T cells generated in vivo. Thus, the mouse GrB ELISPOT may be used to detect cytotoxic responses, at the single-cell level, for the functional assessment of antigen-specific CD8+ T cell responses in mouse models of infection.

Epitope mapping of Ly-49G and G-like receptors: CK-1 antibody defines a polymorphic site of functional interaction with class I ligand.

Ly-49 receptors regulate mouse natural killer cell functions. Members of the polymorphic Ly-49 multigene family recognize specific alleles of major histocompatibility complex class I (MHC I) or MHC I-like proteins. Previous studies have provided insight into the nature of Ly-49A and -C interaction with their high-affinity MHC I ligands, H-2Dd and Kb, respectively. Unlike Ly-49C, recognition of MHC I by Ly-49A is regulated in part by residues within the beta4-beta5 loop of its ectodomain. Ly-49A and -G are within the same Ly-49 subfamily, and both receptors recognize Dd. However, there have been no studies that define specific sites on Ly-49G that mediate class I MHC recognition. The Ly-49G receptors of different inbred mouse strains can differ as a result of amino acid polymorphisms within their ectodomains. In this report, we have generated a novel antibody, CK-1, which recognizes Ly-49G(B6) and a Ly-49G(B6)-like receptor, Ly-49M(nonobese diabetic), but not Ly-49G(BALB/c). By exploiting the differences within ectodomains of C57BL/6 and BALB/c Ly-49G allele products, we identified epitopes recognized by the Ly-49G-specific antibodies CK-1 and Cwy-3, whose epitopes mapped within the beta4-beta5 loop and the beta1 strand, respectively, and were nonoverlapping. Although both antibodies specifically recognized the Ly-49G(B6) ectodomain, Cwy-3 was unable to block its interaction with MHC I, and CK-1 significantly inhibited it. The importance of residues within the beta4-beta5 loop in Ly-49G recognition demonstrates that its interaction with MHC I is similar to that of Ly-49A but not Ly-49C.

Ly-49 receptors and their functions.

Ly-49 receptors are lectin-like type II transmembrane disulfide-bonded homodimers expressed on natural killer (NK) cells and some T-cell subsets. Cell-mediated cytotoxicity and release of cytokines/chemokines are functions regulated by Ly-49 recognition of class I major histocompatibility complex proteins (MHC-I) or virus-encoded MHC-like product(s). Here we examine diversity and conservation found within the Ly-49 gene family and explore the importance of polymorphism in Ly-49 receptor expression, specificity, and function. Several parallels are evident between Ly-49 receptors in rodents and killer Ig-related (KIR) receptors in humans, including receptor gene amplification and diversification, expression patterns, MHC-I specificity, shared signaling, and ultimate effects on NK-cell functions. These similarities suggest that insights gained in defining Ly-49 receptor functions in small animal models could have direct relevance to existing clinical challenges where there may be opportunities to manipulate human NK cells and KIR receptors for therapeutic benefit.

Identities of P2 and P3 Residues of H-2Kb-Bound Peptides Determine Mouse Ly49C Recognition.

Ly49 receptors can be peptide selective in their recognition of MHC-I-peptide complexes, affording them a level of discrimination beyond detecting the presence or absence of specific MHC-I allele products. Despite this ability, little is understood regarding the properties that enable some peptides, when bound to MHC-I molecules, to support Ly49 recognition, but not others. Using RMA-S target cells expressing MHC-I molecules loaded with individual peptides and effector cells expressing the ectodomain of the inhibitory Ly49C receptor, we found that two adjacent amino acid residues, P2 and P3, both buried in the peptide binding groove of H-2Kb, determine mouse Ly49C specificity. If both are aliphatic residues, this is supportive. Whereas, small amino acids at P2 and aromatic amino acids at the P3 auxiliary anchor residue are detrimental to Ly49C recognition. These results resemble those with a rat Ly49 where the identity of a peptide anchor residue determines recognition, suggesting that dependence on specific peptide residues buried in the MHC-I peptide-binding groove may be fundamental to Ly49 peptide selectivity and recognition.

A novel cytotoxicity assay to evaluate antigen-specific CTL responses using a colorimetric substrate for Granzyme B.

We have utilized the unique enzymatic properties of a key cytotoxic mediator in target cell destruction, Granzyme B (GrB), to establish an attractive alternative to 51Cr-release assays for the assessment of antigen-specific CTL responses. A number of potential colorimetric peptide substrates were compared to evaluate levels of GrB activity in cytolytic cells. The most specific and sensitive substrate for GrB was Ac-IEPD-pNA, as shown by the minimal enzymatic hydrolysis in apoptotic Jurkat cells and strong hydrolysis in human NK cells. When human peripheral blood lymphocytes were stimulated in vitro, elevated GrB levels were detected by both Ac-IEPD-pNA and a GrB ELISA. Analysis of allo-antigen-specific murine CTLs revealed that GrB exocytosis was only detectable upon challenge with appropriate allogeneic target cells and strongly correlated to 51Cr-release data. The validity of using Ac-IEPD-pNA in vaccine trials was demonstrated in mice immunized with allogeneic P815 cells, where GrB enzymatic activity was measurable in ex vivo splenocytes cell cultures only upon co-incubation with P815 targets. Additionally, influenza-infected mice were also assessed for GrB activity following in vitro peptide-stimulation of splenocytes and strongly reflected both peptide-specific tetramer staining and 51Cr-release results. The novel cytotoxic assay presented here should give investigators a sensitive, cross-species, nonradioactive alternative to 51Cr-release assays as a means to assess antigen-specific CTL responses in vaccine trials.

Esomeprazole 40 mg and 20 mg is efficacious in the long-term management of patients with endoscopy-negative gastro-oesophageal reflux disease: a placebo-controlled trial of on-demand therapy for 6 months.

BACKGROUND: On-demand therapy may offer an effective approach to the long-term management of gastro-oesophageal reflux disease (GORD) without oesophagitis. AIM: To examine the efficacy of the novel proton pump inhibitor esomeprazole as on-demand therapy in endoscopy-negative GORD. PATIENTS AND METHODS: Endoscopy-negative GORD patients who achieved complete resolution of heartburn after short-term esomeprazole or omeprazole treatment (n = 721) were randomized to esomeprazole 20 mg (n = 282), 40 mg (n = 293) or placebo (n = 146) on demand (maximum one dose/day) for 6 months. The primary and secondary efficacy endpoints were time to study discontinuation due to (i) unwillingness to continue and (ii) inadequate control of heartburn, respectively. RESULTS: Both doses of esomeprazole were more effective than placebo. During the 6-month period, 42% of placebo recipients discontinued treatment due to unwillingness to continue, compared with 8% and 11% of esomeprazole 20 mg and 40 mg recipients, respectively. Overall, more patients treated with esomeprazole were free from gastrointestinal symptoms after 6 months of on-demand therapy. CONCLUSIONS: Esomeprazole 20 mg was superior to placebo for on-demand treatment of GORD; a higher dose did not confer additional clinical benefit. Over 90% of patients were willing to continue on-demand treatment with esomeprazole 20 mg over a 6-month period.

Granzyme H induces cell death primarily via a Bcl-2-sensitive mitochondrial cell death pathway that does not require direct Bid activation.

Natural killer and T cell-mediated cytotoxicity is important for the elimination of viruses and transformed cells. The granule lytic pathway utilizes perforin and granzymes to induce cell death, while receptor-mediated lytic pathways rely on molecules such as FasL. Pro-apoptotic activities of Granzyme B (GrB) and Fas are well-established, and many of their cellular targets have been identified. However, humans express additional related granzymes - GrA, GrM, GrK, and GrH. Neither the cytotoxic potential of GrH, nor the mechanism by which GrH may induce target cell death is currently understood. We proposed that GrH would have pro-apoptotic activity that would be distinct from that of GrB and FasL, which could be relevant when Fas/FasL or GrB activity or death pathways were impaired. Our results, using a purified recombinant form of GrH, revealed that GrH induced cell death via a Bcl-2-sensitive mitochondrial pathway without direct processing of Bid. Additionally, neither the apoptosome nor caspase-3 was essential to the induction of GrH-mediated cell death. However, GrH did directly process DFF45, potentially leading to DNA damage. Our findings support the idea that multiple, non-redundant death pathways may be initiated by cytotoxic cells to counteract various immune evasion strategies.

Determining ligand specificity of Ly49 receptors.

Ly49 receptors in rodents, like KIR in humans, play an integral role in the regulation of NK cell activity. Some inhibitory Ly49 are known to interact with specific MHC I alleles to maintain tolerance to self tissues, and NK activation is triggered upon the loss of inhibitory signals due to pathological downregulation of self MHC I. Although a virally encoded ligand has been identified that can trigger NK cytotoxicity through an activating Ly49, some activating Ly49 also recognize MHC I and the role of most activating receptors in NK effector function remains poorly defined. As many Ly49 remain orphan receptors, we describe methods to unambiguously discern receptor-ligand pairs. Additionally, we describe a method for the mutagenesis of Ly49 and MHC ligands that can be used to define the motifs conferring receptor specificity for their ligands. Further elucidation of Ly49 ligands is required to continue to define the role of Ly49 in regulating NK cell effector function and may give vital clues to the role of KIR in human health and disease.

Granzyme B: Correlates with protection and enhanced CTL response to influenza vaccination in older adults.

This study compared serum antibody titers and granzyme B (GrzB) levels in virus-stimulated peripheral blood mononuclear cells following influenza vaccination. Twelve of 239 older adults who subsequently developed laboratory-diagnosed influenza illness (LDI) had significantly lower GrzB levels compared to subjects without LDI (p=0.004). Eight subjects with LDI in the previous year showed an enhanced GrzB response to vaccination (p=0.02). Serum antibody titers following vaccination did not distinguish those older adults who developed LDI from those who did not. These results suggest that GrzB levels could be combined with antibody titers to more effectively predict vaccine efficacy in older adults.

IL-15 transpresentation augments CD8+ T cell activation and is required for optimal recall responses by central memory CD8+ T cells.

Although the adaptive immune system has a remarkable ability to mount rapid recall responses to previously encountered pathogens, the cellular and molecular signals necessary for memory CD8(+) T cell reactivation are poorly defined. IL-15 plays a critical role in memory CD8(+) T cell survival; however, whether IL-15 is also involved in memory CD8(+) T cell reactivation is presently unclear. Using artificial Ag-presenting surfaces prepared on cell-sized microspheres, we specifically addressed the role of IL-15 transpresentation on mouse CD8(+) T cell activation in the complete absence of additional stimulatory signals. In this study we demonstrate that transpresented IL-15 is significantly more effective than soluble IL-15 in augmenting anti-CD3epsilon-induced proliferation and effector molecule expression by CD8(+) T cells. Importantly, IL-15 transpresentation and TCR ligation by anti-CD3epsilon or peptide MHC complexes exhibited synergism in stimulating CD8(+) T cell responses. In agreement with previous studies, we found that transpresented IL-15 preferentially stimulated memory phenotype CD8(+) T cells; however, in pursuing this further, we found that central memory (T(CM)) and effector memory (T(EM)) CD8(+) T cells responded differentially to transpresented IL-15. T(CM) CD8(+) T cells undergo Ag-independent proliferation in response to transpresented IL-15 alone, whereas T(EM) CD8(+) T cells are relatively unresponsive to transpresented IL-15. Furthermore, upon Ag-specific stimulation, T(CM) CD8(+) T cell responses are enhanced by IL-15 transpresentation, whereas T(EM) CD8(+) T cell responses are only slightly affected, both in vitro and in vivo. Thus, our findings distinguish the role of IL-15 transpresentation in the stimulation of distinct memory CD8(+) T cell subsets, and they also have implications for ex vivo reactivation and expansion of Ag-experienced CD8(+) T cells for immunotherapeutic approaches.