Lymphocyte-mediated cytotoxicity in vitro and in vivo: mechanisms and significance

Rubella vaccine-induced granulomas are a novel phenotype with incomplete penetrance of genetic defects in cytotoxicity

BACKGROUND

Rubella virus-induced granulomas have been described in patients with various inborn errors of immunity. Most defects impair T-cell immunity, suggesting a critical role of T cells in rubella elimination. However, the molecular mechanism of virus control remains elusive.

OBJECTIVE

This study sought to understand the defective effector mechanism allowing rubella vaccine virus persistence in granulomas.

METHODS

Starting from an index case with Griscelli syndrome type 2 and rubella skin granulomas, this study combined an international survey with a literature search to identify patients with cytotoxicity defects and granuloma. The investigators performed rubella virus immunohistochemistry and PCR and T-cell migration assays.

RESULTS

This study identified 21 patients with various genetically confirmed cytotoxicity defects, who presented with skin and visceral granulomas. Rubella virus was demonstrated in all 12 accessible biopsies. Granuloma onset was typically before 2 years of age and lesions persisted from months to years. Granulomas were particularly frequent in MUNC13-4 and RAB27A deficiency, where 50% of patients at risk were affected. Although these proteins have also been implicated in lymphocyte migration, 3-dimensional migration assays revealed no evidence of impaired migration of patient T cells. Notably, patients showed no evidence of reduced control of concomitantly given measles, mumps, or varicella live-attenuated vaccine or severe infections with other viruses.

CONCLUSIONS

This study identified lymphocyte cytotoxicity as a key effector mechanism for control of rubella vaccine virus, without evidence for its need in control of live measles, mumps, or varicella vaccines. Rubella vaccine-induced granulomas are a novel phenotype with incomplete penetrance of genetic disorders of cytotoxicity.

Interferon Gamma and Contact-dependent Cytotoxicity Are Each Rate Limiting for Natural Killer Cell-Mediated Antibody-dependent Chronic Rejection

Natural killer (NK) cells are key components of the innate immune system. In murine cardiac transplant models, donor-specific antibodies (DSA), in concert with NK cells, are sufficient to inflict chronic allograft vasculopathy independently of T and B cells. In this study, we aimed to determine the effector mechanism(s) required by NK cells to trigger chronic allograft vasculopathy during antibody-mediated rejection. Specifically, we tested the relative contribution of the proinflammatory cytokine interferon gamma (IFN-γ) versus the contact-dependent cytotoxic mediators of perforin and the CD95/CD95L (Fas/Fas ligand [FasL]) pathway for triggering these lesions. C3H/HeJ cardiac allografts were transplanted into immune-deficient C57BL/6 rag-/- γc-/- recipients, who also received monoclonal anti-major histocompatibility complex (MHC) class I DSA. The combination of DSA and wild-type NK cell transfer triggered aggressive chronic allograft vasculopathy. However, transfer of IFN-γ-deficient NK cells or host IFN-γ neutralization led to amelioration of these lesions. Use of either perforin-deficient NK cells or CD95 (Fas)-deficient donors alone did not alter development of vasculopathy, but simultaneous disruption of NK cell-derived perforin and allograft Fas expression resulted in prevention of these abnormalities. Therefore, both NK cell IFN-γ production and contact-dependent cytotoxic activity are rate-limiting effector pathways that contribute to this form of antibody-induced chronic allograft vasculopathy.

The CD70/CD27 pathway is critical for stimulation of an effective cytotoxic T cell response against B cell precursor acute lymphoblastic leukemia

For effective immunotherapy, maintaining the frequency and cytotoxic potential of effector cells is critical. In this context costimulation via the CD70/CD27 pathway has been proven essential. CD70 has been reported to be expressed to varying degrees on malignant B cells. However, in B cell precursor acute lymphoblastic leukemia, the most common childhood malignancy, the role of CD70 in stimulation of antileukemic T cell responses has so far not been delineated. Herein we demonstrate that in B cell precursor acute lymphoblastic leukemia expression of CD70 is low but can be induced upon blast activation via CD40. Both CD70 and CD80/CD86 up-regulated on CD40-stimulated blasts contribute to primary stimulation of T cell proliferation and cytokine production in an additive manner. These two signals also cooperate in the prevention of T cell anergy. In contrast to blockade of CD70 during the effector phase, inhibition of CD70-mediated costimulation during generation of antileukemic T cells prevents effector cell proliferation and reduces their cytotoxic capacity. Modulation of the CD70/CD27 pathway may thus represent a novel therapeutic approach for augmenting magnitude and quality of the antileukemic response in B cell precursor acute lymphoblastic leukemia.

MyD88 intrinsically regulates CD4 T-cell responses

Myeloid differentiation factor 88 (MyD88) is an essential adaptor protein in the Toll-like receptor-mediated innate signaling pathway, as well as in interleukin-1 receptor (IL-1R) and IL-18R signaling. The importance of MyD88 in the regulation of innate immunity to microbial pathogens has been well demonstrated. However, its role in regulating acquired immunity to viral pathogens and neuropathogenesis is not entirely clear. In the present study, we examine the role of MyD88 in the CD4(+) T-cell response following lymphocytic choriomeningitis virus (LCMV) infection. We demonstrate that wild-type (WT) mice developed a CD4(+) T-cell-mediated wasting disease after intracranial infection with LCMV. In contrast, MyD88 knockout (KO) mice did not develop wasting disease in response to the same infection. This effect was not the result of MyD88 regulation of IL-1 or IL-18 responses since IL-1R1 KO and IL-18R KO mice were not protected from weight loss. In the absence of MyD88, naïve CD4(+) T cells failed to differentiate to LCMV-specific CD4 T cells. We demonstrated that MyD88 KO antigen-presenting cells are capable of activating WT CD4(+) T cells. Importantly, when MyD88 KO CD4(+) T cells were reconstituted with an MyD88-expressing lentivirus, the rescued CD4(+) T cells were able to respond to LCMV infection and support IgG2a antibody production. Overall, these studies reveal a previously unknown role of MyD88-dependent signaling in CD4(+) T cells in the regulation of the virus-specific CD4(+) T-cell response and in viral infection-induced immunopathology in the central nervous system.

Cytokine and antibody responses in gnotobiotic pigs after infection with human norovirus genogroup II.4 (HS66 strain)

A human norovirus genogroup II.4 strain HS66 (HuNoV-HS66) infects and causes mild diarrhea in gnotobiotic (Gn) pigs (S. Cheetham, M. Souza, T. Meulia, S. Grimes, M. G. Han, and L. J. Saif, J. Virol. 80:10372-10381, 2006). In this study we evaluated systemic and intestinal humoral and cellular immune responses to HuNoV-HS66 in orally inoculated pigs. Antibodies and type I interferon (IFN-I or IFN-alpha), proinflammatory interleukin-6 (IL-6), Th1 (IL-12 and IFN-gamma), Th2 (IL-4), and Th2/regulatory T ([T(reg)] IL-10) cytokine profiles in serum and intestinal contents (IC) of the HuNoV-HS66-inoculated pigs and controls were assessed by enzyme-linked immunosorbent assay at selected postinoculation days (0 to 28). Using an enzyme-linked immunospot assay, we evaluated immunoglobulin M (IgM), IgA, and IgG antibody-secreting cells (ASC) and cytokine-secreting cells (CSC) in intestine, spleen, and blood. In the HuNoV-inoculated pigs, antibody titers in serum and IC were generally low, and 65% seroconverted. Pigs with higher diarrhea scores were more likely to seroconvert and developed higher intestinal IgA and IgG antibody titers. The numbers of IgA and IgG ASC were higher systemically than in the gut. In serum, HuNoV induced persistently higher Th1 (low transient IFN-gamma and high IL-12) than the other cytokines, but also low Th2 (IL-4) and Th2/T(reg) (IL-10) levels; low, transient proinflammatory (IL-6) cytokines; and, notably, a delayed IFN-alpha response. In contrast, intestinal innate (IFN-alpha early and late) and Th1 (IL-12 late) cytokines were significantly elevated postinfection. HuNoV-HS66 also elicited higher numbers of Th1 (IL-12 and IFN-gamma) CSC than Th2 (IL-4) and proinflammatory (IL-6) CSC, with the latter responses low in blood and intestine, reflecting low intestinal inflammation in the absence of gut lesions. These data provide insights into the kinetics of cytokine secretion in serum and IC of HuNoV-inoculated Gn pigs and new information on intestinal humoral and cellular immune responses to HuNoV that are difficult to assess in human volunteers.

CD8(+) T cell-mediated immune responses in West Nile virus (Sarafend strain) encephalitis are independent of gamma interferon

The flavivirus West Nile virus (WNV) can cause fatal encephalitis in humans and mice. It has recently been demonstrated, in an experimental model using WNV strain Sarafend and C57BL/6 mice, that both virus- and immune-mediated pathology is involved in WNV encephalitis, with CD8(+) T cells being the dominant subpopulation of lymphocyte infiltrates in the brain. Here, the role of activated WNV-immune CD8(+) T cells in mouse WNV encephalitis was investigated further. Passive transfer of WNV-immune CD8(+) T cells reduced mortality significantly and prolonged survival times of mice infected with WNV. Early infiltration of WNV-immune CD8(+) T cells into infected brains is shown, suggesting a beneficial contribution of these lymphocytes to recovery from encephalitis. This antiviral function was not markedly mediated by gamma interferon (IFN-gamma), as a deficiency in IFN-gamma did not affect mortality to two strains of WNV (Sarafend and Kunjin) or brain virus titres significantly. The cytolytic potential, as well as precursor frequency, of WNV-immune CD8(+) T cells were not altered by the absence of IFN-gamma. This was reflected in transfer experiments of WNV-immune CD8(+) T cells from IFN-gamma(-/-) mice into WNV-infected wild-type mice, which showed that IFN-gamma-deficient T cells were as effective as those from WNV-immune wild-type mice in ameliorating disease outcome. It is speculated here that one of the pleiotropic functions of IFN-gamma is mimicked by WNV-Sarafend-mediated upregulation of cell-surface expression of major histocompatibility complex antigens, which may explain the lack of phenotype of IFN-gamma(-/-) mice in response to WNV.

Herpes simplex virus genes Us3, Us5, and Us12 differentially regulate cytotoxic T lymphocyte-induced cytotoxicity

Many viruses, including Herpes Simplex Virus (HSV), have developed strategies to avoid detection by cytotoxic T lymphocytes (CTLs). In this article, we evaluated the role of individual HSV-1 genes in preventing cytolysis and apoptosis, and in decreasing viral yield after CTL exposure of HSV-infected fibroblasts, using viruses deleted for the immune evasion gene Us12 or one of the two antiapoptotic genes Us3 and Us5. To evaluate CTL-mediated apoptosis, we used a flow cytometry assay measuring active caspase-3 in target cells. This assay was more sensitive than the chromium release assay used to evaluate cytolysis, and measured a different aspect of CTL cytotoxicity. Although virus with deletion of Us12 was markedly defective in the ability to prevent lysis of target fibroblasts, it retained most of its ability to protect target fibroblasts from CTL-induced apoptosis. Virus with deletion of Us3 was also defective in the ability to prevent lysis of target fibroblasts, yet such virus protected target fibroblasts from CTL-induced apoptosis as well as wild-type viruses. In contrast, Us5-deleted virus showed defects in the ability to protect target fibroblasts from both cytolysis and apoptosis after CTL attack. In addition, the replication of Us12-deleted virus was reduced compared with wild-type virus in fibroblasts subjected to CTL attack 6 h after infection, but showed equivalent replication when CTL attack occurred later. In contrast, Us3- or Us5-deleted virus showed no measurable defect in their ability to replicate in fibroblasts under CTL attack. Our data suggest that cytolysis, apoptosis, and viral yield do not necessarily correlate in infected cells under CTL attack. Furthermore, the Us3, Us5, and Us12 viral genes each have unique inhibitory effects on the different T lymphocyte cytotoxic effects. Taken together, these results suggest that HSV evasion of cellular immunity is multifacterial and complex, and relies on the partially redundant activities of various individual HSV proteins.

Rapid Functional Exhaustion and Deletion of CTL following Immunization with Recombinant Adenovirus

Replication-deficient adenoviruses (recombinant adenovirus (rec-AdV)) expressing different transgenes are widely used vectors for gene therapy and vaccination. In this study, we describe the tolerization of transgene-specific CTL following administration of beta-galactosidase (beta gal)-recombinant adenovirus (Ad-LacZ). Using MHC class I tetramers to track beta gal-specific CTL, we found that a significant expansion of beta gal-specific CTL was restricted to a very narrow dose range. Functional analysis revealed that adenovirus-induced beta gal-specific CTL produced only very low amounts of effector cytokines and were unable to exhibit cytolytic activity in a 51Cr release assay. Furthermore, Ad-LacZ vaccination failed to efficiently clear established beta gal-positive tumors. The impaired function of Ad-LacZ-induced CTL correlated with the presence of persisting beta gal Ag in the liver. A further increase in the peripheral Ag load by injection of Ad-LacZ into SM-LacZ transgenic mice which express beta gal as self-Ag exclusively in peripheral nonlymphoid organs, resulted in the physical deletion of beta gal-specific CTL. Our results indicate first that CTL deletion in the course of adenoviral vaccination is preceded by their functional impairment and second, that the outcome of rec-AdV vaccination depends critically on the Ag load in peripheral tissues.

Different Diabetogenic Potential of Autoaggressive CD8+ Clones Associated with IFN-γ-Inducible Protein 10 (CXC Chemokine Ligand 10) Production but Not Cytokine Expression, Cytolytic Activity, or Homing Characteristics

Type 1 diabetes mellitus is an autoimmune disease characterized by T cell-mediated destruction of the insulin-producing beta cells in the islets of Langerhans. From studies in animal models, CD8(+) T cells recognizing autoantigens such as islet-specific glucose-6-phosphatase catalytic subunit-related protein, insulin, or glutamic acid decarboxylase (GAD) are believed to play important roles in both the early and late phases of beta cell destruction. In this study, we investigated the factors governing the diabetogenic potential of autoreactive CD8(+) clones isolated from spleens of NOD mice that had been immunized with GAD65(515-524) or insulin B-chain(15-23) peptides. Although these two clones were identical in most phenotypic and functional aspects, for example cytokine production and killing of autologous beta cells, they differed in the expression of IFN-gamma-inducible protein-10, which was only produced at high levels by the insulin-specific clone, but not by the GAD65-specific clone, and other autoantigen-specific nonpathogenic CD8 T cell clones. Interestingly, upon i.p. injection into neonatal mice, only the insulin B-chain(15-23)-reactive CD8(+) T clone accelerated diabetes in all recipients after 4 wk, although both insulin- and GAD-reactive clones homed to pancreas and pancreatic lymph nodes with similar kinetics. Diabetes was associated with increased pancreatic T cell infiltration and, in particular, recruitment of macrophages. Thus, secretion of IFN-gamma-inducible protein-10 by autoaggressive CD8(+) lymphocytes might determine their diabetogenic capacity by affecting recruitment of cells to the insulitic lesion.

Immune responses against SARS-coronavirus nucleocapsid protein induced by DNA vaccine

The nucleocapsid (N) protein of SARS-coronavirus (SARS-CoV) is the key protein for the formation of the helical nucleocapsid during virion assembly. This protein is believed to be more conserved than other proteins of the virus, such as spike and membrane glycoprotein. In this study, the N protein of SARS-CoV was expressed in Escherichia coli DH5α and identified with pooled sera from patients in the convalescence phase of SARS. A plasmid pCI-N, encoding the full-length N gene of SARS-CoV, was constructed. Expression of the N protein was observed in COS1 cells following transfection with pCI-N. The immune responses induced by intramuscular immunization with pCI-N were evaluated in a murine model. Serum anti-N immunoglobulins and splenocytes proliferative responses against N protein were observed in immunized BALB/c mice. The major immunoglobulin G subclass recognizing N protein was immunoglobulin G2a, and stimulated splenocytes secreted high levels of gamma interferon and IL-2 in response to N protein. More importantly, the immunized mice produced strong delayed-type hypersensitivity (DTH) and CD8⁺ CTL responses to N protein. The study shows that N protein of SARS-CoV not only is an important B cell immunogen, but also can elicit broad-based cellular immune responses. The results indicate that the N protein may be of potential value in vaccine development for specific prophylaxis and treatment against SARS.

Mapping herpes simplex virus type 1 latency-associated transcript sequences that protect from apoptosis mediated by a plasmid expressing caspase-8

LAT (latency-associated transcript) is the only herpes simplex virus type 1 (HSV-1) transcript abundantly expressed during neuronal latency. LAT expression is required for the high reactivation phenotype of HSV-1 and this phenotype correlates with LAT's anti-apoptosis properties. LAT nucleotides 1 to 1499 inhibit caspase-8 (death receptor apoptotic pathway), but not caspase-9 (mitochondrial apoptotic pathway), -induced apoptosis as efficiently as larger LAT fragments. LAT sequences important for inhibiting caspase-8-induced apoptosis were also localized. The ability of LAT nucleotides 1 to 1499 to efficiently inhibit caspase-8-induced apoptosis correlates with the high reactivation phenotype of a mutant virus expressing just the first 1.5 kb of LAT (nucleotides 1 to 1499).

Granzymes in cytolytic lymphocytes--to kill a killer?

Granzymes (gzm) are major components of the granules of cytolytic lymphocytes, natural killer and cytotoxic T cells. Their generally accepted mode of action consists of their directed secretion towards a virus-infected or neoplastic target cell and perforin-dependent delivery to the target cell cytosol, where they engage in various actions resulting in target cell apoptosis. Here, based on observations of infection of gzmAxB(-/-) mice with ectromelia virus, mousepox, we propose an additional--and distinct--function for gzmA and B. In this model, gzm constitute one of the first lines of defence of immune cells against virus infection of immune cells themselves. Accordingly, endogenous gzm interfere with viral replication in cytolytic lymphocytes either directly, as a result of their proteolytic activity, leading to destruction of viral proteins, or indirectly, via: (i) processes akin to the caspase cascade when acting as effector molecules in the induction of target cell apoptosis; or (ii) their capacity to induce early inflammatory mediators. We discuss the predictions of the model in the light of available data.

HTLV-1 carriers with B-cell lymphoma of localized stage head and neck: prognosis, clinical and immunopathological features

Human T-lymphotropic virus type I (HTLV-I) is closely associated with T-cell lymphoma/leukaemia, which always shows monoclonal HTLV-1 provirus DNA integration. HTLV-1 is not associated with B-cell lymphoma. The relationship between B-cell lymphoma and HTLV-1 was analysed retrospectively in early stage B-cell non-Hodgkin's lymphoma (NHL) according to HTLV-1 infection and pathological features. We analysed 198 cases of head and neck B-cell NHL treated with radiotherapy and/or chemotherapy; 21 were seropositive and 177 were seronegative for HTLV-1. We also immunostained 26 cases of diffuse large B-cell lymphoma (DLBL), including 12 seropositive and 14 seronegative for HTLV-1 respectively, for CD20, CD3, CD4, CD8, CD56, MIB-1 and T-cell-restricted intracellular antigen (TIA-1) to examine the phenotype, immunity and proliferation activity. The 5-year overall survival rates were 78% and 49% (P = 0.007, log rank test) for HTLV-1 seronegative and seropositive cases respectively. Infection with HTLV-1 was significantly associated with poor survival in patients with B-cell lymphoma by multivariate analysis. For DLBL, HTLV-1 infection was not a significant factor, but the overall survival curve was similar to that of the 21 seropositive B-cell lymphoma cases. Lymphoma cells were negative for TIA-1, but the background lymphocytes were positive for this marker. The number of TIA-1-positive cells was higher in HTLV-1-negative cases than in-positive cases. In conclusion, patients with B-cell-NHL (B-NHL) who are also HTLV-1 carriers have a poorer prognosis than non-carriers. HTLV-1 does not seem to be associated with lymphomagenesis of the B phenotype itself, but correlates with host immunity by reducing the number of cytotoxic T-cells.

Discordant expression of perforin and granzyme A in total and HIV-specific CD8 T lymphocytes of HIV infected children and adolescents

OBJECTIVE

Perforin and granzyme are cytotoxic effector molecules that are believed to play essential roles in cytotoxic T cell (CTL) activity. We tested the hypothesis that dysregulation of these effector molecules contributes to defects of CD8 antiviral immune responses in pediatric subjects in chronic stages of perinatal HIV infection.

DESIGN/METHOD

Studies of CD8 T cells were conducted in 33 treatment experienced HIV+ patients (median age, 10.6 years) and in 14 age-matched healthy controls. CD8 T cells specific for HIV Gag and Pol peptides were identified in HLA-A2+ patients by tetramer binding assays. HIV-specific and total CD8 T cells were examined for perforin, granzyme and expression of CD27, a marker that is lost in terminally differentiated cells.

RESULTS

Three populations of CD8 T cells were identified: granzyme+ perforin+; granzyme+ perforin- and cells negative for both perforin and granzyme. In HIV infected patients, granzyme+ cells were increased in total CD8 T cells (39% versus 13% in controls) and were highest in HIV Gag-specific CD8 cells (42%). Perforin+ CD8 T cells were approximately fivefold fewer than granzyme+ CD8 T cells and were enriched in CD27 negative cells. Most HIV-specific CD8 cells were CD27+. Granzyme expression in CD8 T cells correlated negatively with CD4 percentage and positively with virus load.

CONCLUSION

A disproportionate and generalized increase in CD27+, granzyme+, CD8 T cells is a hallmark of established pediatric HIV infection. These findings support the concept of skewed maturation, with failure of CD8 T cells to mature into perforin-enriched, CD27-negative, effector cells.

Apoptosis prevention as a mechanism of immune evasion

When cells are infected with viruses, they may trigger their apoptosis programs. In unicellular organisms, this may have protected cell populations by limiting viral replication from infected cells. Multicellular organisms can also trigger the apoptosis program after viral infection. In response, viruses have evolved a wide variety of inhibitors of apoptosis. In higher organisms, the outcome of viral infections is largely determined by the immune system. Since apoptosis is intimately linked to the function and regulation of the immune system, the ability of viruses to inhibit apoptosis could profoundly alter the immune response. Viral antiapoptotic proteins could protect infected cells from apoptosis induced by cytotoxic lymphocytes, alter antigen cross-presentation and the priming of the immune response, or modulate the expression of danger signals from sites of infection. The virus/host interaction is likely to provide useful lessons regarding the workings of the mammalian immune system.

A novel domain in adenovirus L4-100K is required for stable binding and efficient inhibition of human granzyme B: possible interaction with a species-specific exosite

Lymphocyte granule serine proteases (granzymes) play a critical role in protecting higher organisms against intracellular infections and cellular transformation. The proteases have also been implicated in the generation of tissue damage in a variety of chronic human conditions, including autoimmunity and transplant rejection. Granzyme B (GrB), one cytotoxic member of this family, achieves its effect through cleavage and activation of caspases as well as through caspase-independent proteolysis of cellular substrates. The 100,000-molecular-weight (100K) assembly protein of human adenovirus type 5 (Ad5-100K) was previously defined as a potent and specific inhibitor of human GrB. We now show that although human, mouse, and rat GrB proteases are well conserved in terms of structure, substrate specificity, and function, Ad5-100K inhibitory activity is directed exclusively against the human protease. Biochemical analysis demonstrates that the specificity of the 100K protein for human GrB resides in two distinct interactions with the protease: (i) a unique sequence within the reactive site loop (P(1))Asp(48)-(P(1'))Pro(49) in Ad5-100K which interacts with the active site and (ii) the presence of an additional inhibitor-enzyme interaction likely outside the enzyme catalytic site (i.e., an exosite). We have located this extended macromolecular interaction site in Ad5-100K within amino acids 688 to 781, and we have demonstrated that this region is essential for stable inhibitor-enzyme complex formation as well as efficient inhibition of human GrB. This novel component of the inhibitory mechanism of the 100K protein identifies a distinct target for selective inhibitor design, a finding which may be of benefit for diseases in which GrB plays a pathogenic role.

Cell-mediated cytotoxicity in recovery from poxvirus infections

The availability of mutant and gene targeted knockout mice with defects in components of cellular cytotoxicity mediated by either the Fas or the exocytosis pathway permitted an analysis of their role in recovery from poxvirus infections. Ectromelia (EV), a natural mouse pathogen causing mousepox, the closely related orthopoxviruses cow pox (CPV) and vaccinia virus (VV), each encode serpins that inhibit Fas mediated apoptosis and lysis of target cells. Nevertheless, distinct differences were seen when the three viruses were inoculated into perforin-deficient mice: highly resistant C57Bl/6 mice became susceptible to low doses of EV; resistance to CPV increased whereas there was no effect on VV infections. Absence of the cytolytic granule associated granzymes (gzm) A and B rendered C57Bl/6 mice increasingly more susceptible to EV infections. Lack of both gzms rendered them as susceptible as perforin deficient mice, despite the presence of functionally active perforin. Elevated EV titres in liver and spleen of gzmA x B deficient mice, early after infection and before cytotoxic T cells were detectable, strongly suggests that these two gzms exert an antiviral effect by a mechanism distinct from effector molecules of NK and cytotoxic T cells.

Local immune responses to influenza virus infection in mice with a targeted disruption of perforin gene

The role of perforin in the local defense mechanisms against influenza virus infection was investigated. Mice deficient in the perforin gene (perforin(-/-)) were more susceptible to influenza virus infection than the ordinary wild-type C57BL/6 mice, showing an increased mortality with elevated virus growth and prolonged virus shedding. The lung parenchyma cells of perforin(-/-) mice showed no cytolytic activities of natural killer cells or virus-specific cytotoxic T lymphocytes in vitro, although the local antibody production system in the respiratory tract functioned well. In perforin(-/-) mice, the appearance of apoptotic degeneration in virally infected lung cells was delayed. This might cause cellular infiltration, including CD4, CD8, and CD19 positive cells, in the lung, peaking at day 8 after infection and maintaining a high level for a longer period. In the virus-induced local cytokine production, interferon-gamma (IFN-gamma) was prominent. The adoptive transfer of immune-competent spleen cells from wild-type C57BL/6 mice achieved a complete protection of perforin(-/-) mice against lethal challenge infection. These results suggest that perforin plays a crucial role in the host defense system against influenza virus infection, especially in its early stage, by inducing apoptosis of virus-infected cells.

Perforin-mediated effector function within the central nervous system requires IFN-gamma-mediated MHC up-regulation

CD8(+) T cells infiltrating the CNS control infection by the neurotropic JHM strain of mouse hepatitis virus. Differential susceptibility of infected cell types to clearance by perforin or IFN-gamma uncovered distinct, nonredundant roles for these antiviral mechanisms. To separately evaluate each effector function specifically in the context of CD8(+) T cells, pathogenesis was analyzed in mice deficient in both perforin and IFN-gamma (PKO/GKO) or selectively reconstituted for each function by transfer of CD8(+) T cells. Untreated PKO/GKO mice were unable to control the infection and died of lethal encephalomyelitis within 16 days, despite substantially higher CD8(+) T cell accumulation in the CNS compared with controls. Uncontrolled infection was associated with limited MHC class I up-regulation and an absence of class II expression on microglia, coinciding with decreased CD4(+) T cells in CNS infiltrates. CD8(+) T cells from perforin-deficient and wild-type donors reduced virus replication in PKO/GKO recipients. By contrast, IFN-gamma-deficient donor CD8(+) T cells did not affect virus replication. The inability of perforin-mediated mechanisms to control virus in the absence of IFN-gamma coincided with reduced class I expression. These data not only confirm direct antiviral activity of IFN-gamma within the CNS but also demonstrate IFN-gamma-dependent MHC surface expression to guarantee local T cell effector function in tissues inherently low in MHC expression. The data further imply that IFN-gamma plays a crucial role in pathogenesis by regulating the balance between virus replication in oligodendrocytes, CD8(+) T cell effector function, and demyelination.

Control of lymphocytic choriomeningitis virus infection in granzyme B deficient mice

We have investigated whether granzyme B (GzmB) is required for effective cytotoxic T lymphocyte (CTL) mediated control of lymphocytic choriomeningitis virus (LCMV) infection. Clearance of LCMV from tissues of GzmB-deficient (GzmB-) mice following intraperitoneal infection with LCMV was impaired compared with control mice; however, the virus was ultimately eliminated. The impaired clearance of LCMV in GzmB- mice was not due to a deficiency in the generation of LCMV-specific T cells. In addition, CTL from LCMV-infected GzmB- mice efficiently lysed virus-infected cells in vitro, but were deficient in their ability to induce rapid DNA fragmentation in target cells. We examined whether the development of protective immunity against intracranial (i.c.) rechallenge with LCMV was compromised in GzmB- mice. We found that clearance of LCMV from the brain following secondary i.c. infection also was slower in the absence of GzmB; however, the virus was ultimately eliminated and the mice survived. Our data indicate that clearance of LCMV is delayed in the absence of GzmB expression, but that other CTL effector molecules can compensate for the absence of this granule constituent in vivo.

Localization of Fas ligand in cytoplasmic granules of CD8+ cytotoxic T lymphocytes and natural killer cells: participation of Fas ligand in granule exocytosis model of cytotoxicity

Fas ligand (FasL) has been implicated in cytotoxic T lymphocyte (CTL)- and natural killer (NK) cell-mediated cytotoxicity. In the present study, we investigated the localization of FasL in murine CTL and NK cells. Immunocytochemical staining showed that FasL was stored in cytoplasmic granules of CD8+ CTL clones and in vivo activated CTL and NK cells, where perforin and granzyme A also resided. Immunoelectron microscopy revealed that FasL was localized on outer membrane of the cytoplasmic granules, while perforin was localized in internal vesicles. Western blot analysis showed that the membrane-type FasL of 40 kDa was stored in CD8+ CTL clones but not in CD4+ CTL clones. By utilizing a granule exocytosis inhibitor (TN16), we demonstrated that FasL translocated onto cell surface upon degranulation of anti-CD3-stimulated CD8+ CTL clones. Moreover, TN16 markedly inhibited the FasL-mediated cytotoxicity by CD8+ T cell clones and NK cells. These results suggested a substantial contribution of FasL to granule exocytosis-mediated target cell lysis by CD8+ CTL and NK cells.

Antigen-dependent release of IFN-gamma by cytotoxic T cells up-regulates Fas on target cells and facilitates exocytosis-independent specific target cell lysis

Effector cytolytic T (Tc) lymphocytes, deficient in the exocytosis-mediated pathway of target cell lysis, induce Fas on target cells and, in turn, delayed cell death and apoptosis via the Fas ligand-Fas interaction. The induction of Fas can be blocked by anti- IFN-gamma Abs. This Fas up-regulation on initially Fas-negative target cells is not mediated by TCR-MHC/peptide signaling per se, but by secreted IFN-gamma from Tc cells after Ag engagement. The Fas up-regulation by Tc cells can be mimicked by treatment of target cells with rIFN-gamma. Tc cells from IFN-gamma knockout mice do not induce Fas expression on target cells. Tc cell-mediated Fas expression on third party, bystander, target cells does not enhance their susceptibility to lysis by these nominal effector cells. The results are discussed as to the possible relevance of the phenomenon in efficiency and regulation of the Tc cell response to infections by viruses.

Role of T cells in development of chronic pancreatitis in male Wistar Bonn/Kobori rats: effects of tacrolimus

We assessed T cell association with acinar cell apoptosis and a preventive effect of tacrolimus, a T cell suppressant, on the development of chronic pancreatitis in male Wistar Bonn/Kobori rats. At 15 wk, cellular infiltrates composed of F4/80-positive cells (monocytes/macrophages), CD4-positive cells, and CD8-positive cells were extensive in the interlobular connective tissue and parenchyma. In particular, CD8-positive cells invaded pancreatic lobules and formed close associations with acinar cells, some of which demonstrated features of apoptosis. At 20 wk, CD8-positive cells were still abundant in the fibrotic tissue formed with loss of acinar cells. Repeated subcutaneous injection of 0.1 mg x kg(-1) x day(-1) but not 0.025 mg x kg(-1) x day(-1) of tacrolimus for 10 wk completely prevented the occurrence of acinar cell apoptosis, infiltration of CD4- and CD8-positive cells, and development of pancreatitis at the age of 20 wk, but these maneuvers did not recover the decreased plasma corticosterone levels, which may be responsible for the development of disease. We demonstrated that T cells, possibly CD8-positive cells, are involved in inducing apoptosis of acinar cells, raising the possibility that tacrolimus might find clinical application in the treatment of autoimmune chronic pancreatitis.

Rejection of intraocular tumors by CD4(+) T cells without induction of phthisis

Immune privilege of the eye protects against sight-threatening inflammatory events, but can also permit outgrowth of otherwise nonlethal immunogenic tumors. Nonetheless, ocular tumor growth can be controlled by cellular immune responses. However, this will normally result in phthisis of the eye, in case tumor rejection is mediated by a delayed-type hypersensitivity response orchestrated by CD4(+) T cells. We now show that intraocular tumors can be eradicated by CD4(+) Th cells without inducing collateral damage of neighboring ocular tissue. Injection of tumor cells transformed by the early region 1 of human adenovirus type 5 in the anterior chamber of the eye leads to intraocular tumor formation. Tumor growth is transient in immunocompetent mice, but lethal in immunodeficient nude mice, indicating that T cell-dependent immunity is responsible for tumor clearance. Tumor rejection has all the characteristics of a CD8(+) T cell-mediated immune response, as the tumor did not express MHC class II and only tumor tissue was the subject of destruction. However, analysis of the molecular and cellular mechanisms involved in tumor clearance revealed that perforin, TNF-alpha, Fas ligand, MHC class I, and CD8(+) T cells did not play a crucial role in tumor eradication. Instead, effective tumor rejection was entirely dependent on CD4(+) Th cells, as CD4-depleted as well as MHC class II-deficient mice were unable to reject their intraocular tumor. Taken together, these observations demonstrate that CD4(+) T cells are able to eradicate MHC class II-negative tumors in an immune-privileged site without affecting surrounding tissues or the induction of phthisis.

An improved protocol for measuring cytotoxic T cell activity in anatomic compartments with low cell numbers

The study of target cell lysis and cytokine production are valuable tools to characterize antigen-specific T and NK cell function during virus infections. After localized infections in compartments such as the lung or the brain, however, cell numbers isolated from these organs are too low to perform standard assays with individual mice. Here, we report a few simple modifications of the classical 51Cr release assay allowing reduction of the number of required effector cells by a factor of 10 without loosing sensitivity or specificity. Using not more than 4x10(5) effector cells, we were able to study ex vivo virus-specific CTL or NK activity from the lungs of individual mice after infection with respiratory syncytial virus (RSV) and from the brains of mice infected with Borna disease virus (BDV). Flow cytometric analysis of interferon-gamma production by virus-specific T cells including appropriate controls was achieved with as few as 10(5) effector cells.

Expression of cutaneous lymphocyte-associated antigen and TIA-1 by lymphocytes in pityriasis lichenoides et varioliformis acuta and lymphomatoid papulosis: immunohistochemical study

BACKGROUND

Pityriasis lichenoides et varioliformis acuta (PLEVA) and lymphomatoid papulosis (LyP) are benign self-healing cutaneous eruptions that may be clinically and histologically similar. The purposes of this study were to evaluate immunohistological characteristics of PLEVA and LyP and to investigate whether Epstein-Barr virus (EBV) may be present in PLEVA and LyP.

METHODS

We performed an immunohistochemical staining in 12 cases of PLEVA and 8 cases of LyP using nine antibodies for CD3, CD4, CD8, CD30, CD45RO, CD56, CD79, cutaneous lymphocyte-associated antigen (CLA), and TIA-1. In situ hybridization was performed using fluorescein-conjugated oligonucleotide probes for EBV early regions (EBER).

RESULTS

In PLEVA, immunohistochemical studies revealed that infiltrated lymphocytes consisted of mainly CD3-positive (5+), CD8-positive (4+ to 5+), CLA-positive (4+ to 5+) T cells and partly CD79 positive (+ to 2+) B cells. CD4-positive T cells were less than 25%. In LyP, immunohistochemical studies revealed that infiltrated lymphocytes consisted of partly CD3-positive (5+), CD8-positive (2+ to 3+), CLA-positive (3+ to 4+) T cells and partly CD79-positive (2+ to 3+) B cells. CD4-positive T cells were less than 10%. CD8 and CLA were more strongly expressed in PLEVA than in LyP. CD30 was strongly expressed in LyP but not expressed in PLEVA. CD79 was more expressed in LyP than in PLEVA. TIA-1 was not expressed in any cases. In situ hybridization using antisense EBER probe showed negative reaction in all cases.

CONCLUSIONS

Immunohistochemical stains for CD8, CD30, CD79 and CLA may be valuable tools in the differential diagnosis between PLEVA and LyP. TIA-1 was negative in LyP, which means cytotoxic cells may not be implicated in the pathogenesis of LyP. It was a contradictory result to the previous results. The absence of EBV in PLEVA and LyP suggests that this virus may not be operative in the pathogenesis of these diseases. These results suggest that LyP and PLEVA are separate disorders, thus accounting for their variable prognosis.

Dressed to kill? A review of why antiviral CD8 T lymphocytes fail to prevent progressive immunodeficiency in HIV-1 infection

CD8 T cells play an important role in protection and control of HIV-1 by direct cytolysis of infected cells and by suppression of viral replication by secreted factors. However, although HIV-1-infected individuals have a high frequency of HIV-1-specific CD8 T cells, viral reservoirs persist and progressive immunodeficiency generally ensues in the absence of continuous potent antiviral drugs. Freshly isolated HIV-specific CD8 T cells are often unable to lyse HIV-1-infected cells. Maturation into competent cytotoxic T lymphocytes may be blocked during the initial encounter with antigen because of defects in antigen presentation by interdigitating dendritic cells or HIV-infected macrophages. The molecular basis for impaired function is multifactorial, due to incomplete T-cell signaling and activation (in part related to CD3zeta and CD28 down-modulation), reduced perforin expression, and inefficient trafficking of HIV-specific CD8 T cells to lymphoid sites of infection. CD8 T-cell dysfunction can partially be corrected in vitro with short-term exposure to interleukin 2, suggesting that impaired HIV-specific CD4 T helper function may play a significant causal or exacerbating role. Functional defects are qualitatively different and more severe with advanced disease, when interferon gamma production also becomes compromised.

Concerted action of the FasL/Fas and perforin/granzyme A and B pathways is mandatory for the development of early viral hepatitis but not for recovery from viral infection

Cytotoxic T lymphocytes (CTL) play a major role in the recovery from primary viral infections and the accompanying tissue injuries. However, it is unclear to what extent the two main cytolytic pathways, perforin-granzyme A and B exocytosis and Fas ligand (FasL)-Fas interaction, contribute to these processes. Here we have employed mouse strains with either spontaneous mutations or targeted gene defects in one or more components of either of the two cytolytic pathways to analyze the molecular basis of viral clearance and induction of hepatitis during lymphocytic choriomeningitis virus infection. Our results reveal that viral clearance is solely dependent on perforin but that virus-induced liver damage only occurs when both the FasL/Fas and the perforin pathways, including granzymes A and B, are simultaneously activated. The finding that development of hepatitis but not viral clearance is dependent on the concomitant activation of FasL-Fas and perforin-granzymes may be helpful in designing novel strategies to prevent hepatic failures during viral infections.

Perforin and Fas in murine gammaherpesvirus-specific CD8(+) T cell control and morbidity

The immune system uses both virus-specific T cells and B cells to control the acute and latent phases of respiratory infection with the murine gammaherpesvirus 68 (gammaHV-68). We sought to further define the important effector mechanisms for CD8(+) T cells. First, depletion of the CD4(+) T cells resulted in a failure of most animals to drive the virus into latency, although lytic virus in the lung was reduced by approximately 1000-fold from its peak. Second, the absence of either perforin or Fas alone had no impact on the ability to reduce titres of lytic virus in the lung. Further neutralization of IFN-gamma in CD4-depleted P(+/+), P(-/-) or Fas(-/-) mice had no effect. To define the requirements for Fas or perforin more clearly, two sets of chimeric mice were constructed differing in perforin expression by the T cells, and Fas on infected epithelial cells or lymphocytes. Animals with P(-/-) T cells and a Fas(-/-) lung failed to limit the shedding of infectious virus, regardless of whether CD4 T cells were present. In addition, we noted that having P(-/-) T cells in irradiated Fas(+/+) hosts caused a lethal disease that was not apparent in the non-chimeric (unirradiated) P(-/-) (Fas(+/+)) mice. In another set of chimeric mice, P(-/-) T cells were able to limit persistent infection of B cells that expressed Fas, but not B cells that were Fas-deficient. These studies demonstrate that some degree of cytotoxicity via either perforin or Fas is essential for CD8(+) T cells to control this DNA virus.

A dual role for TNF-alpha in type 1 diabetes: islet-specific expression abrogates the ongoing autoimmune process when induced late but not early during pathogenesis

We report here that islet-specific expression of TNF-alpha can play a dual role in autoimmune diabetes, depending on its precise timing in relation to the ongoing autoimmune process. In a transgenic model (rat insulin promoter-lymphocytic choriomeningitis virus) of virally induced diabetes, TNF-alpha enhanced disease incidence when induced through an islet-specific tetracycline-dependent promoter system early during pathogenesis. Blockade of TNF-alpha during this phase prevented diabetes completely, suggesting its pathogenetic importance early in disease development. In contrast, TNF-alpha expression abrogated the autoimmune process when induced late, which was associated with a reduction of autoreactive CD8 lymphocytes in islets and their lytic activities. Thus, the fine-tuned kinetics of an autoreactive process undergo distinct stages that respond in a differential way to the presence of TNF-alpha. This observation has importance for understanding the complex role of inflammatory cytokines in autoimmunity.

Adenovirus L4-100K assembly protein is a granzyme B substrate that potently inhibits granzyme B-mediated cell death

Cytotoxic lymphocytes kill virus-infected target cells and play a critical role in host recovery from viral infections. Granzyme B (GrB) is a cytotoxic lymphocyte granule protease that plays a critical role in mediating cytotoxicity. In these studies, we demonstrate that the adenovirus assembly protein L4--100K (100K) is a GrB substrate that prevents cytotoxic lymphocyte granule-induced apoptosis in infected target cells by potently inhibiting GrB. This inhibition is absolutely dependent on Asp-48 in 100K, found within a classic GrB consensus motif. 100K is the first viral protein described that exclusively targets the GrB pathway. It represents a novel class of viral protease inhibitor, in which an essential, multifunctional viral protein, which is vulnerable to specific proteolysis by GrB, expresses inhibitory function against that protease.

Characterization of T cell responses to fragrances

Fragrances are worldwide a major cause of allergic contact dermatitis (ACD), a delayed-type hypersensitivity reaction mediated by T lymphocytes. We investigated T cell responses to fragrances using peripheral blood mononuclear cells (PBMC) and T cells from skin lesions of fragrance-allergic patients. The components of a fragrance mixture (eugenol, isoeugenol, geraniol, oak moss, alpha-amyl cinnamic aldehyde, cinnamic aldehyde, cinnamic alcohol, and hydroxycitronellal) that is commonly used in the patch test were studied in vitro in the lymphocyte transformation test (LTT). PBMC from fragrance-allergic patients (n = 32) showed significant stimulations to all eight fragrances. The calculated stimulation indices (SI) varied between 2.1 and 21.8. The influence of metabolic enzymes on T cell stimulation was studied for two fragrances. Interestingly, stimulation of eugenol and isoeugenol was increased in the presence of antigen-modified human liver microsomes (CYP450) or recombinant CYP1A1 in five of seven cases. Furthermore, we established 18 T cell clones (TCC) from a skin lesion reacting specifically to eugenol. FACS analysis revealed that the majority (n = 15, 83%) of TCC were CD3(+), CD4(+), and HLA-DR(+). Seventeen percent (n = 3) of the clones were CD8(+). TCC (n = 4) released significant amounts of IL-2 and IFN-gamma but no IL-4 and IL-5. In addition, CD4(+) TCC (n = 3) showed antigen-induced cytotoxic activities against autologous B cells. In summary, we demonstrated for the first time that fragrance-specific CD4(+) and CD8(+) T lymphocytes are present in fragrance-allergic individuals. In addition, our results suggest that CYPs can be involved in the formation of the nominative antigen.

Fas ligand costimulates the in vivo proliferation of CD8+ T cells

Fas ligand (FasL/CD95L/APO-1L) is one of a growing number of TNF family members whose triggering costimulates maximal proliferation of activated T cells. In this study we show that maximal Ag-dependent accumulation of transferred TCR-transgenic CD8(+) T cells requires Fas (CD95/APO-1) expression by the adoptive hosts. Additionally, adoptively transferred FasL(+) CD8(+) T cells demonstrate a 2-fold advantage in Ag-driven expansion over their FasL(-)counterparts. This study illustrates the in vivo role of TCR-dependent FasL costimulation in the Ag-specific proliferation of both heterogeneous and homogeneous populations of primary CD8(+) T cells and long-term CTL lines. Thus, cross-linking FasL on naive and Ag-experienced CD8(+) T cells whose Ag-specific TCRs are engaged is required to drive maximal cellular proliferation in vivo.

Cytotoxic T cells specifically induce Fas on target cells, thereby facilitating exocytosis-independent induction of apoptosis

Cytotoxic T (Tc) cells deficient in perforin lyse Fas-negative targets after lengthy incubation periods. This process is independent of granzymes, and killing occurs via the Fas pathway for the following reasons. Interaction of perforin-deficient Tc cells with Fas-negative targets leads to an up-regulation of Fas that is dependent on Ag recognition, de novo synthesis, and transport of proteins to the target cell surface. Treatment of effectors with brefeldin A, but not with the exocytosis inhibitor concanamycin, inhibited this process. Lysis of targets is inhibited by anti-Fas Abs, soluble mouse Fas-Fc, and the caspase-cascade inhibitor, crm-A. Targets from Fas-mutant lpr mice are refractory to lysis, and Tc cells from mice deficient in Fas- and perforin-mediated lysis do not lyse Fas-negative targets. The possible relevance of this exocytosis-independent cytolytic process in the regulation of T cell activity and control of pathogens is discussed.

Gastrointestinal T cell lymphoma: predominant cytotoxic phenotypes, including alpha/beta, gamma/delta T cell and natural killer cells

Gastrointestinal T cell lymphoma (TCL) is a rare subset of peripheral TCL, presenting with or without cytotoxic phenotype, a history of coeliac disease (CD) and enteropathy. However, CD is rare in Japan. Here, we describe the clinicopathological features of 18 Japanese cases. Lesions were found in the small intestine (n=13), stomach (n=3) and colon (n=2). Seven patients presented with enteropathy but none had a history of CD. Lymphomas appeared as ulceration (n=11), tumour formation (n=6), or polypoid growth (n=1). Histologically (REAL classification), neoplastic lesions were composed of intestinal type T cell lymphoma (ITCL, n=13, including one case with NK type), anaplastic large cell (ALCL, n=2), adult T cell leukaemia/lymphoma (ATLL, n=2), and lymphoblastic type (n=1). Epstein Barr virus infection was detected by EBER-1 in situ hybridization in 6 of 11 cases with ITCL but not in the other types. ALCL expressed CD30. CD56 was expressed in 3 of 11 cases of ITCL but not in other types. Among the 10 examined cases, 8 were alphabeta T cell type [CD2+, CD3+, T cell receptor (TCR)delta-1-, betaF1+], one was gammadelta T cell type [CD2+, CD3+, TCRdelta-1+, betaF1-], and the remaining case expressed natural killer (NK) cell type [CD2+, CD3-, CD56+, TCRdelta-1-, betaF1-]. Among the 8 examined cases, 3 expressed CD103 molecule, which was associated with extrathymic T cells of intraepithelial lymphocytes. All cases except ATLL expressed the cytotoxicity-associated molecule of TIA-1, and 11 of 14 TIA-1 positive cases expressed activated cytotoxic molecules of perforin, granzyme B, and/or Fas ligand. Despite the morphological, genetic and phenotypic heterogeneity, prognosis was poor, and 11 of 13 patients with small intestinal lesions died albeit appropriate treatment, but 3 of 4 patients with gastric or colonic lesions were still alive. The main cause of death was intestinal perforation. The latter might be due to the site specificity of small intestine and tumour cytotoxicity.

CD3ζ and CD28 down-modulation on CD8 T cells during viral infection

Down-modulation of CD3ζ expression on CD8 T lymphocytes occurs, independently of other T-cell receptor (TCR)-CD3 components, in tumor-infiltrating lymphocytes, human immunodeficiency virus infection, and autoimmune disease. These associations suggest that it might be related to chronic antigenic stimulation. CD3ζ down-modulation was found, however, in CD8 T cells that proliferate in response to acute viral infections. In 3 otherwise healthy donors with acute gastroenteritis, infectious mononucleosis, and Epstein–Barr virus/cytomegalovirus/mononucleosis, 30% to 60% of circulating CD8 T cells had down-modulated CD3ζ to below the level of detection. The CD3ζ-T cells were also CD28− but expressed the activation markers HLA-DR and CD57. CD3ζ–CD28– T cells are effector CTL because they express perforin and produce IFN-γ, but not IL-2, on activation and contain the viral-specific cytotoxic T lymphocyte (CTL). However, CD3ζ–CD28–T cells generally do not express CD25 after anti-CD3 and anti-CD28 stimulation and are not cytotoxic until they are cultured with IL-2 overnight. Cytotoxicity coincides with the re-expression of CD3ζ but not CD28. Down-modulation of CD3ζ and CD28 on effector CTL may control CTL triggering and proliferation to prevent immunopathogenesis.

CD3ζ and CD28 down-modulation on CD8 T cells during viral infection

Down-modulation of CD3ζ expression on CD8 T lymphocytes occurs, independently of other T-cell receptor (TCR)-CD3 components, in tumor-infiltrating lymphocytes, human immunodeficiency virus infection, and autoimmune disease. These associations suggest that it might be related to chronic antigenic stimulation. CD3ζ down-modulation was found, however, in CD8 T cells that proliferate in response to acute viral infections. In 3 otherwise healthy donors with acute gastroenteritis, infectious mononucleosis, and Epstein–Barr virus/cytomegalovirus/mononucleosis, 30% to 60% of circulating CD8 T cells had down-modulated CD3ζ to below the level of detection. The CD3ζ-T cells were also CD28− but expressed the activation markers HLA-DR and CD57. CD3ζ–CD28– T cells are effector CTL because they express perforin and produce IFN-γ, but not IL-2, on activation and contain the viral-specific cytotoxic T lymphocyte (CTL). However, CD3ζ–CD28–T cells generally do not express CD25 after anti-CD3 and anti-CD28 stimulation and are not cytotoxic until they are cultured with IL-2 overnight. Cytotoxicity coincides with the re-expression of CD3ζ but not CD28. Down-modulation of CD3ζ and CD28 on effector CTL may control CTL triggering and proliferation to prevent immunopathogenesis.

IL-1alpha, IL-1beta, and IFN-gamma mark beta cells for Fas-dependent destruction by diabetogenic CD4(+) T lymphocytes

Cytokines such as IL-1alpha, IL-1beta, and IFN-gamma have long been implicated in the pathogenesis of autoimmune diabetes, but the mechanisms through which they promote diabetogenesis remain unclear. Here we show that CD4(+) T lymphocytes propagated from transgenic nonobese diabetic (NOD) mice expressing the highly diabetogenic, beta cell-specific 4.1-T-cell receptor (4.1-TCR) can kill IL-1alpha-, IL-1beta-, and IFN-gamma-treated beta cells from NOD mice. Untreated NOD beta cells and cytokine-treated beta cells from Fas-deficient NOD.lpr mice are not targeted by these T cells. Killing of islet cells in vitro was associated with cytokine-induced upregulation of Fas on islet cells and was independent of MHC class II expression. Abrogation of Fas expression in 4.1-TCR-transgenic NOD mice afforded nearly complete protection from diabetes and did not interfere with the development of the transgenic CD4(+) T cells or with their ability to cause insulitis. In contrast, abrogation of perforin expression did not affect beta cell-specific cytotoxicity or the diabetogenic potential of these T cells. These data demonstrate a novel mechanism of action of IL-1alpha, IL-1beta, and IFN-gamma in autoimmune diabetes, whereby these cytokines mark beta cells for Fas-dependent lysis by autoreactive CD4(+) T cells.

Primary CD30-positive cutaneous T-cell lymphomas and lymphomatoid papulosis frequently express cytotoxic proteins

AIMS

To analyse the relationship between expression of cytotoxic proteins, histopathology and the CD30 status in primary cutaneous T-cell disorders, we investigated the expression of TIA-1, granzyme B and perforin in CD30 negative and CD30 positive cutaneous T-cell lymphomas (CTCL) and lymphomatoid papulosis (LP).

METHODS AND RESULTS

We studied 26 cases of CTCL and 12 cases of LP for the expression of TIA-1, granzyme B and perforin which are granule-associated proteins of cytotoxic lymphocytes involved in the mechanism of apoptosis. We showed that most cases (10/13) of CD30 negative pleomorphic lymphomas expressed cytotoxic proteins only in scattered, apparently reactive lymphocytes, the exception being one CD8+ CTCL and two gammadelta subcutaneous 'panniculitis-like' T-cell lymphomas. We also showed that at least one cytotoxic protein was expressed in a proportion of neoplastic cells in 77% (10/13) of CD30+ T-cell lymphomas (3/4 pleomorphic and 7/9 anaplastic) and in a proportion of atypical cells in 75% (9/12) of LP.

CONCLUSIONS

Our findings show a strong correlation between the CD30 phenotype and the expression of cytotoxic proteins in primary CTCL. In addition, these results provide further evidence for an overlap between lymphomatoid papulosis and cutaneous CD30+ pleomorphic and anaplastic lymphomas. These entities, which belong to the spectrum of CD30 positive cutaneous T-cell lymphoproliferations, appear to be derived from cytotoxic cells.

Granzymes are the essential downstream effector molecules for the control of primary virus infections by cytolytic leukocytes

Analysis of perforin-deficient mice has identified the cytolytic pathway and perforin as the preeminent effector molecule in T cell-mediated control of virus infections. In this paper, we show that mice lacking both granzyme A (gzmA) and granzyme B (gzmB), which are, beside perforin, key constituents of cytolytic vesicles, are as incapable as are perforin-deficient mice of controlling primary infections by the natural mouse pathogen ectromelia, a poxvirus. Death of gzmAxgzmB double knockout mice occurred in a dose-dependent manner, despite the expression of functionally active perforin and the absence of an intrinsic defect to generate splenic cytolytic T cells. These results establish that both gzmA and gzmB are indispensable effector molecules acting in concert with perforin in granule exocytosis-mediated host defense against natural viral pathogens.

Viral-Specific Cytotoxic T Lymphocytes Lyse Human Immunodeficiency Virus–Infected Primary T Lymphocytes by the Granule Exocytosis Pathway

Cytotoxic T lymphocytes (CTL) lyse antigen-bearing target cells by two distinct pathways. Whereas granule exocytosis targets any antigen-bearing cell, fas-mediated cytotoxicity kills only fas-expressing cells and does not require antigen expression. Fas pathway activation can potentially lead to lysis of uninfected bystander cells. We examined the relative usage of the two pathways by CTL clones and cell lines directed against four different human immunodeficiency virus (HIV) proteins in lysing primary HIV-infected targets. Although fas was expressed on HIV-infected primary CD4+ T cells, their lysis by antigen-specific CD8+ CTL was only by the granule pathway. Fas ligand (fasL) was not detectable on antigen-specific CD8 clones, T-cell lines, or circulating HIV-specific CD8 T cells from HIV-infected donors, stained with a tetrameric HLA-A2-HIV-peptide complex. FasL expression by HIV-specific CTL clones was not activated by exposure to HIV-presenting cells, but was after unphysiological stimulation with phorbol myristate acetate (PMA). CTL clones did not lyse bystander Jurkat cells, but HIV-infected primary CD4+ T cells lysed uninfected bystander cells by the fas-mediated pathway. These results suggest that HIV-specific CD8+ CTL do not cause HIV immunopathology by lysing bystander cells. On the contrary, fas-mediated lysis of uninfected cells by HIV-infected cells may contribute to CD4 decline.

Viral-Specific Cytotoxic T Lymphocytes Lyse Human Immunodeficiency Virus–Infected Primary T Lymphocytes by the Granule Exocytosis Pathway

Cytotoxic T lymphocytes (CTL) lyse antigen-bearing target cells by two distinct pathways. Whereas granule exocytosis targets any antigen-bearing cell, fas-mediated cytotoxicity kills only fas-expressing cells and does not require antigen expression. Fas pathway activation can potentially lead to lysis of uninfected bystander cells. We examined the relative usage of the two pathways by CTL clones and cell lines directed against four different human immunodeficiency virus (HIV) proteins in lysing primary HIV-infected targets. Although fas was expressed on HIV-infected primary CD4+ T cells, their lysis by antigen-specific CD8+ CTL was only by the granule pathway. Fas ligand (fasL) was not detectable on antigen-specific CD8 clones, T-cell lines, or circulating HIV-specific CD8 T cells from HIV-infected donors, stained with a tetrameric HLA-A2-HIV-peptide complex. FasL expression by HIV-specific CTL clones was not activated by exposure to HIV-presenting cells, but was after unphysiological stimulation with phorbol myristate acetate (PMA). CTL clones did not lyse bystander Jurkat cells, but HIV-infected primary CD4+ T cells lysed uninfected bystander cells by the fas-mediated pathway. These results suggest that HIV-specific CD8+ CTL do not cause HIV immunopathology by lysing bystander cells. On the contrary, fas-mediated lysis of uninfected cells by HIV-infected cells may contribute to CD4 decline.

Poxvirus-Encoded Serpins Do Not Prevent Cytolytic T Cell-Mediated Recovery from Primary Infections

Previous observations that the highly conserved poxvirus-encoded serpins inhibit cytotoxic activities of alloreactive CTL via granule and/or Fas-mediated pathways was taken to indicate their involvement in immune evasion by poxviruses. We now show that interference with 51Cr release from target cells by ectromelia and cowpoxvirus is limited to alloreactive but not MHC-restricted CTL. The data are in support of the paramount importance of CTL and its effector molecule perforin in the recovery from primary ectromelia virus infection and question the role of serpins in the evasion of poxviruses from killing by CTL. Further analysis of poxvirus interference with target cell lysis by alloreactive CTL revealed that suppression primarily affects the Fas-mediated, and to a lesser extent, the granule exocytosis pathway. Serpin-2 is the main contributor to suppression for both killing pathways. In addition, inhibition of lysis was shown to be both target cell type- and MHC allotype-dependent. We hypothesize that differences in TCR affinities and/or state of activation between alloreactive and MHC-restricted CTL as well as the quality (origin) of target cells are responsible for the observed phenomenon.

Soluble HLA Class I, HLA Class II, and Fas Ligand in Blood Components: A Possible Key to Explain the Immunomodulatory Effects of Allogeneic Blood Transfusions

The immunomodulatory effect of allogeneic blood transfusions (ABT) has been known for many years. However, a complete understanding of the effects of ABT on the recipient’s immune system has remained elusive. Soluble HLA class I (sHLA-I), HLA class II (sHLA-II), and Fas ligand (sFasL) molecules may play immunoregulatory roles. We determined by double-determinant immunoenzymatic assay (DDIA) sHLA-I, sHLA-II, and sFasL concentrations in different blood components. sHLA-I and sFasL levels in red blood cells (RBCs) stored for up to 30 days and in random-donor platelets are significantly (P < .001) higher than in other blood components and their amount is proportionate to the number of residual donor leukocytes and to the length of storage. Blood components with high sHLA-I and sFasL levels play immunoregulatory roles in vitro as in allogeneic mixed lymphocyte responses (MLR) and antigen-specific cytotoxic T-cell (CTL) activity, and induce apoptosis in Fas-positive cells. These data suggest that soluble molecules in blood components are functional. If these results are paralleled in vivo, they should be taken into account in transfusion practice. Blood components that can cause immunosuppression should be chosen to induce transplantation tolerance, whereas blood components that lack immunosuppressive effects should be preferred to reduce the risk of postoperative complications and cancer recurrence.

Soluble HLA Class I, HLA Class II, and Fas Ligand in Blood Components: A Possible Key to Explain the Immunomodulatory Effects of Allogeneic Blood Transfusions

The immunomodulatory effect of allogeneic blood transfusions (ABT) has been known for many years. However, a complete understanding of the effects of ABT on the recipient’s immune system has remained elusive. Soluble HLA class I (sHLA-I), HLA class II (sHLA-II), and Fas ligand (sFasL) molecules may play immunoregulatory roles. We determined by double-determinant immunoenzymatic assay (DDIA) sHLA-I, sHLA-II, and sFasL concentrations in different blood components. sHLA-I and sFasL levels in red blood cells (RBCs) stored for up to 30 days and in random-donor platelets are significantly (P &lt; .001) higher than in other blood components and their amount is proportionate to the number of residual donor leukocytes and to the length of storage. Blood components with high sHLA-I and sFasL levels play immunoregulatory roles in vitro as in allogeneic mixed lymphocyte responses (MLR) and antigen-specific cytotoxic T-cell (CTL) activity, and induce apoptosis in Fas-positive cells. These data suggest that soluble molecules in blood components are functional. If these results are paralleled in vivo, they should be taken into account in transfusion practice. Blood components that can cause immunosuppression should be chosen to induce transplantation tolerance, whereas blood components that lack immunosuppressive effects should be preferred to reduce the risk of postoperative complications and cancer recurrence.