Biomedical subjects

M Kopf

Publications and source records attributed to M Kopf.

At least 37 records · Page 2Linked to original sources

PubMed1999

Developmental regulation of Lck targeting to the CD8 coreceptor controls signaling in naive and memory T cells.

The question of whether enhanced memory T cell responses are simply due to an increased frequency of specific cells or also to an improved response at the single cell level is widely debated. In this study, we analyzed T cell receptor (TCR) transgenic memory T cells and bona fide memory T cells isolated from virally infected normal mice using the tetramer technology. We found that memory T cells are qualitatively different from naive T cells due to a developmentally regulated rearrangement of the topology of the signaling machinery. In naive cytotoxic T cells, only a few CD8 molecules are associated with Lck and the kinase is homogeneously distributed inside the cell. However, in vivo priming of naive T cells induces the targeting of Lck to the CD8 coreceptor in the cell membrane and the consequent organization of a more efficient TCR signaling machinery in effector and memory cells.

Acetyltransferases↗

PubMed1999

Distinct kinetics of cytokine production and cytolysis in effector and memory T cells after viral infection.

In the present study, naive T cells were compared with in vivo generated effector and memory T cells expressing the same TCR specific for lymphocytic choriomeningitis virus. Upon restimulation in vitro, the same minimal concentrations of the full agonist peptide p33 and also of weak and partial agonist peptides were required for proliferation of naive, effector and memory T cells, indicating no difference in threshold of activation. However, activation kinetics were distinct. While effector cytotoxic T cells exhibited immediate ex vivo lytic effector function, naive and memory T cells required 12 h and more exposure to antigen to develop lytic activity. However, both effector and memory T cells contained IFN-gamma mRNA in vivo and required less than 3 h for secretion of cytokines upon restimulation in vitro. In contrast, naive T cells did not contain IFN-gamma mRNA and required more than 12 h for cytokine secretion. Our results show that memory T cells exhibit a unique phenotype in that they produce cytokines and commit to proliferation as rapidly as effector cells, whereas they resemble naive T cells in the time requirement for development of cytolytic function.

Animals↗

PubMed1999

Outcome of Staphylococcus aureus-triggered sepsis and arthritis in IL-4-deficient mice depends on the genetic background of the host.

Disruption of the IL-4 gene in two inbred mouse strains revealed a dual role of IL-4 in Staphylococcus aureus sepsis and arthritis depending on the host's genetic background. IL-4 was protective in 129SV mice, since 5 days after S. aureus inoculation IL-4(-/-) mice displayed 70% mortality as compared to survival of all 129SV wild-type counterparts. On the other hand, IL-4 was detrimental in C57BL/6 mice, since survival of IL-4(-/-) C57BL/6 mice was increased, as compared to wild-type controls, due to decreased staphylococcal growth. Altogether, our results show the dual role of IL-4 in S. aureus sepsis and arthritis, depending on the genetic background of the host.

Animals↗

PubMed1999

The role of B cells in acute and chronic infections.

The important role of B cells in protection against secondary viral infections has been recognized for a long time. Recent evidence suggests that B cells are also critically involved in protective immune reactions classically attributed to T cells. Specifically, antibodies have been documented to protect from many primary viral and parasitic infections and to be indispensable for the control of latent viral infections. Current vaccine strategies should take into account this pivotal role of antibodies.

Acute Disease↗

PubMed1999

OX40-deficient mice are defective in Th cell proliferation but are competent in generating B cell and CTL Responses after virus infection.

OX40, a member of the TNF receptor superfamily, is expressed on activated T cells and implicated in stimulation of T cells and T-dependent humoral responses. We generated OX40-/- mice and found that the formation of extrafollicular plasma cells, germinal centers, and antibody responses was independent of OX40. After infection with LCMV and influenza virus, OX40-/- mice retain primary and memory cytotoxic T cell responses with normal expansion and decline of specific CTL. In contrast, CD4+ T cell proliferation and the number of IFN-gamma-producing CD4+ T cells were reduced in OX40-/- mice. Moreover, the number of CD4+ T cells infiltrating the lungs of influenza virus-infected OX40-/- mice was reduced. These results define a unique role of OX40 in the generation of optimal CD4+ T cell responses in vivo.

Animals↗

PubMed1999

Antifungal type 1 responses are upregulated in IL-10-deficient mice.

C57BL/6 mice are highly resistant to infections caused by Candida albicans and Aspergillus fumigatus. To elucidate the role of IL-10 produced by C57BL/6 mice during these infections, parameters of infection and immunity to it were evaluated in IL-10-deficient and wild-type mice with disseminated or gastrointestinal candidiasis or invasive pulmonary aspergillosis. Unlike parasitic protozoan infection, C. albicans or A. fumigatus infection did not induce significant acute toxicity in IL-10-deficient mice, who, instead, showed reduced fungal burden and fungal-associated inflammatory responses. The increased resistance to infections as compared to wild-type mice was associated with upregulation of innate and acquired antifungal Th1 responses, such as a dramatically higher production of IL-12, nitric oxide (NO) and TNF-alpha as well as IFN-gamma by CD4+ T cells. Pharmacological inhibition of NO production greatly reduced resistance to gastrointestinal candidiasis, thus pointing to the importance of IL-10-dependent NO regulation at mucosal sites in fungal infections. These results are reminiscent of those obtained in genetically susceptible mice, in which IL-10 administration increased, and IL-10 neutralization decreased, susceptibility to C. albicans and A. fumigatus infections. Collectively, these observations indicate that the absence of IL-10 augments innate and acquired antifungal immunity by upregulating type 1 cytokine responses. The resulting protective Th1 responses lead to a prompt reduction of fungal growth, thus preventing tissue destruction and lethal levels of proinflammatory cytokines.

Animals↗

PubMed1999

Interleukin-4 causes susceptibility to invasive pulmonary aspergillosis through suppression of protective type I responses.

Aspergillus fumigatus, an opportunistic fungal pathogen, causes multiple allergic and nonallergic airway diseases. Invasive pulmonary aspergillosis (IPA) is a nonallergic, life-threatening disease of immunocompromised patients. In a murine model of IPA, interleukin (IL)-4-deficient (IL-4-/-) BALB/c mice were used to examine the role of IL-4 in lung pathology and immune responses. IL-4-/- mice were more resistant than wild-type mice to infection caused by multiple intranasal injections of viable A. fumigatus conidia. Resistance was associated with decreased lung inflammatory pathology, impaired T helper (Th)-2 responses (including lung eosinophilia), and an IL-12-dependent Th1 response. In contrast, development of host-detrimental antifungal Th2 cells occurred in IL-12-/- and interferon-gamma-/- mice and in IL-4-/- mice when subjected to IL-12 neutralization. These results demonstrate that IL-4 renders mice susceptible to infection with A. fumigatus by inhibition of protective Th1 responses. IL-4 appears to have a distinct role in the pathogenesis of allergic and nonallergic lung diseases caused by the fungus.

Animals↗

PubMed1998

Interleukin 6 influences germinal center development and antibody production via a contribution of C3 complement component.

Mice rendered deficient for interleukin (IL) 6 by gene targeting were evaluated for their response to T cell-dependent antigens. Antigen-specific immunoglobulin (Ig)M levels were unaffected whereas all IgG isotypes showed varying degrees of alteration. Germinal center reactions occurred but remained physically smaller in comparison to those in the wild-type mice. This concurred with the observations that molecules involved in initial signaling events leading to germinal center formation were not altered (e.g., B7.2, CD40 and tumor necrosis factor R1). T cell priming was not impaired nor was a gross imbalance of T helper cell (Th) 1 versus Th2 cytokines observed. However, B7.1 molecules, absent from wild-type counterparts, were detected on germinal center B cells isolated from the deficient mice suggesting a modification of costimulatory signaling. A second alteration involved impaired de novo synthesis of C3 both in serum and germinal center cells from IL-6-deficient mice. Indeed, C3 provided an essential stimulatory signal for wild-type germinal center cells as both monoclonal antibodies that interrupted C3-CD21 interactions and sheep anti-mouse C3 antibodies caused a significant decrease in antigen-specific antibody production. In addition, germinal center cells isolated from C3-deficient mice produced a similar defect in isotype production. Low density cells with dendritic morphology were the local source of IL-6 and not the germinal center lymphocytes. Adding IL-6 in vitro to IL-6-deficient germinal center cells stimulated cell cycle progression and increased levels of antibody production. These findings reveal that the germinal center produces and uses molecules of the innate immune system, evolutionarily pirating them in order to optimally generate high affinity antibody responses.

Animals↗

PubMed1998

Differential effects of the absence of interferon-gamma and IL-4 in acute graft-versus-host disease after allogeneic bone marrow transplantation in mice.

Graft-versus-host disease (GVHD), in which immunocompetent donor cells attack the host, remains a major cause of morbidity after allogeneic bone marrow transplantation (BMT). To understand the role of cytokines in the pathobiology of GVHD, we used cytokine knockout (KO) mice as a source of donor T cells. Two different MHC-disparate strain combinations were examined: BALB/c (H2(d)) donors into lethally irradiated C57BL/6 (H2(b)) recipients or C57BL/6 (H2(b)) donors into B10.BR (H2(k)) recipients. Donor cells were from mice in which either the interferon-gamma (IFN-gamma) or the IL-4 gene was selectively disrupted to understand the role of these cytokines in acute GVHD. In both strain combinations the same pattern was noted with regard to GVHD onset and morbidity. All mice exhibited the classic signs of acute GVHD: weight loss with skin, gut, and liver pathology resulting in morbidity and mortality. Surprisingly, donor cells obtained from mice lacking IFN-gamma gave rise to accelerated morbidity from GVHD when compared with cells from wild-type control donors. Similar results were obtained using normal donors when neutralizing antibodies to IFN-gamma were administered immediately after the BMT. These results suggest that IFN-gamma plays a role in protection from acute GVHD. In marked contrast, cells obtained from IL-4 KO mice resulted in protection from GVHD compared with control donors. Splenocytes from IFN KO mice stimulated with a mitogen proliferated to a significantly greater extent and produced more IL-2 compared with splenocytes obtained from IL-4 KO or control mice. Additionally, there was increased IL-2 production in the spleens of mice undergoing GVHD using IFN-gamma KO donors. These results therefore indicate, with regard to the TH1/ TH2 cytokine paradigm, the absence of a TH1-type cytokine can be deleterious in acute GVHD, whereas absence of a TH2 cytokine can be protective.

Animals↗

PubMed1998

IFN-gamma is required for IL-12 responsiveness in mice with Candida albicans infection.

To elucidate the role of IFN-gamma in antifungal CD4+ Th-dependent immunity, 129/Sv/Ev mice deficient for IFN-gamma receptor (IFN-gammaR(-/-)) were assessed for susceptibility to gastrointestinal or systemic Candida albicans infection and for parameters of innate and adaptive T helper immunity. IFN-gammaR(-/-) mice failed to mount protective Th1-mediated acquired immunity upon mucosal immunization or in response to a live vaccine strain of the yeast. The impaired Th1-mediated resistance correlated with defective IL-12 responsiveness, but not IL-12 production, and occurred in the presence of an increased innate antifungal resistance. The development of nonprotective Th2 responses was observed in IFN-gammaR(-/-) mice upon mucosal infection and subsequent reinfection. However, under experimental conditions of Th2 cell activation, the occurrence of Th2 cell responses was similar in IFN-gammaR(-/-) and in IFN-gammaR(+/+) mice. These results indicate the complex immunoregulatory role of IFN-gamma in the induction of mucosal and nonmucosal anticandidal Th cell responses; IFN-gamma is not essential for the occurrence of Th2 responses but is required for development of IL-12-dependent protective Th1-dependent immunity.

Animals↗

PubMed1998

Interleukin 6 plays a key role in the development of antigen-induced arthritis.

To investigate the direct role of interleukin (IL) 6 in the development of rheumatoid arthritis, IL-6-deficient (IL-6 -/-) mice were backcrossed for eight generations into C57BL/6 mice, a strain of mice with a genetic background of susceptibility for antigen-induced arthritis (AIA). Both histological and immunological comparisons were made between IL-6-deficient (IL-6 -/-) mice and wild-type (IL-6 +/+) littermates after the induction of AIA. Although all IL-6 +/+ mice developed severe arthritis, only mild arthritis was observed in IL-6 -/- mice. Safranin O staining demonstrated that articular cartilage was well preserved in IL-6 -/- mice, whereas it was destroyed completely in IL-6 +/+ mice. In addition, comparable mRNA expression for both IL-1beta and tumor necrosis factor alpha, but not for IL-6, was detected in the inflamed joints of IL-6 -/- mice, suggesting that IL-6 may play a more crucial role in cartilage destruction than either IL-1beta or tumor necrosis factor alpha. In immunological comparisons, both antigen-specific in vitro proliferative response in lymph node cells and in vivo antibody production were elicited in IL-6 -/- mice, but they were reduced to less than half of that found in IL-6 +/+ mice. Lymph node cells of IL-6 -/- mice produced many more Th2 cytokines than did IL-6 +/+ mice with either antigen-specific or nonspecific stimulation in in vitro culture. Taken together, these results indicate that IL-6 may play a key role in the development of AIA at the inductive as well as the effector phase, and the blockade of IL-6 is possibly beneficial in the treatment of rheumatoid arthritis.

Animals↗

PubMed1998

Differences between IL-4R alpha-deficient and IL-4-deficient mice reveal a role for IL-13 in the regulation of Th2 responses.

Allergens and infections with parasitic helminths preferentially induced Th2 immune responses associated with elevated levels of serum immunoglobulin E (IgE) and expansion of eosinophils and mast cells. Interleukin-4 (IL-4) is a key cytokine in the differentiation of naive CD4+ T cells into Th2 cells, which produce a panel of cytokines including IL-4, IL-5, IL-6, IL-9, IL-10, and IL-13 [1] and have been shown to trigger recovery from gastrointestinal nematodes [2]. Nonetheless, mice deficient for IL-4 have been shown to develop residual Th2 responses [3-5] and can expel the nematode Nippostrongylus brasiliensis [6], suggesting that there is a functional equivalent of IL-4 in these processes. IL-13 is a cytokine that shares some, but not all, biological activities with IL-4 [7,8]. There is now compelling evidence that IL-4 and IL-13 share receptor components, including IL-4R alpha and IL-13R alpha 1 [9]. In order to dissect the roles of IL-4 and IL-13 in the regulation of Th2 cells and in the response to nematode infections, we looked for differences between mice deficient for either the IL-4 gene or the IL-4R alpha gene. Unlike IL-4, IL-4R alpha was required for control of N. brasiliensis, and Th2 development during infection--as characterized by cytokine production, GATA-3 and surface CD30 expression--was more severely affected in IL-4R alpha-/- mice than in IL-4-/- mice. Injection of recombinant IL-13 induced worm expulsion in otherwise incompetent RAG2-/- mice. Our results suggest that IL-13 regulates Th2 responses to nematode infection and requires IL-4R alpha.

Animals↗

PubMed1998

Staphylococcus aureus-induced septic arthritis and septic death is decreased in IL-4-deficient mice: role of IL-4 as promoter for bacterial growth.

Lack of IL-4 has been shown to be protective in some experimental models of infectious diseases in mice such as cutaneous leishmaniasis. At the same time IL-4, together with other Th2 cytokines, including IL-10 and IL-13, is known as an anti-inflammatory cytokine with the potential to down-regulate proinflammatory cytokine production. To investigate the role of IL-4 in experimental Staphylococcus aureus-induced and T lymphocyte-mediated arthritis, IL-4-deficient C57BL/6 mice (IL-4(-/-)) and their congenic controls (IL-4(+/+)) were inoculated with a toxic shock syndrome toxin-1-producing S. aureus strain. In IL-4(+/+) mice, arthritis peaked 14 days after bacterial inoculation, whereas, at that time, IL-4(-/-) mice displayed significantly less frequent (p < 0.05) joint inflammation. Paralleling lower frequency of arthritis, IL-4-deficient mice showed a decreased bacterial burden in joints (p = 0.014) and kidneys (p = 0.029), as well as lower infection-triggered weight decrease and mortality. In vitro, IL-4 inhibited intracellular killing of S. aureus in infected macrophages, without affecting phagocytosis. This finding may explain the enhanced staphylococcal clearance observed in IL-4(-/-) mice in vivo. Our results suggest that IL-4 and IL-4-dependent Th2 responses promote septic arthritis and sepsis-related mortality by inhibition of bacterial clearance during S. aureus infection.

Animals↗

PubMed1998

Endogenous interleukin 4 is required for development of protective CD4+ T helper type 1 cell responses to Candida albicans.

Interleukin (IL)-4-deficient mice were used to assess susceptibility to systemic or gastrointestinal Candida albicans infections, as well as parameters of innate and elicited T helper immunity. In the early stage of systemic infection with virulent C. albicans, an unopposed interferon (IFN)-gamma response renders IL-4-deficient mice more resistant than wild-type mice to infection. Yet, IL-4-deficient mice failed to efficiently control infection in the late stage and succumbed to it. Defective IFN-gamma and IL-12 production, but not IL-12 responsiveness, was observed in IL-4-deficient mice that failed to mount protective T helper type 1 cell (Th1)-mediated acquired immunity in response to a live vaccine strain of the yeast or upon mucosal immunization in vivo. In vitro, IL-4 primed neutrophils for cytokine release, including IL-12. However, late treatment with exogenous IL-4, while improving the outcome of infection, potentiated CD4(+) Th1 responses even in the absence of neutrophils. These findings indicate that endogenous IL-4 is required for the induction of CD4(+) Th1 protective antifungal responses, possibly through the combined activity on cells of the innate and adaptive immune systems.

Animals↗

PubMed1998

Neutrophils but not eosinophils are involved in growth suppression of IL-4-secreting tumors.

Local expression of IL-4 by gene-modified tumor cells increases their immunogenicity by inducing an inflammatory response that is dominated by eosinophils. Eosinophils have been implicated as antitumor effector cells because the application of a granulocyte-depleting Ab inhibited rejection of IL-4 transfected tumors. This Ab did not discriminate between eosinophils and neutrophils and, therefore, this experiment could not exclude neutrophils as primary effector cells, whereas eosinophils were innocent bystander cells in IL-4 transfected tumors. We analyzed tumor growth suppression and granulocyte infiltration in IL-5-deficient (IL-5(-/-)) mice that had a deficiency of eosinophils, using two tumor lines (B16-F10 and MCA205) transfected to secrete IL-4. IL-4-expressing tumors were at least as efficiently rejected in IL-5(-/-) mice as in wild-type mice, despite an almost complete absence of tumor-infiltrating eosinophils. However, neutrophils were present in undiminished amounts and their depletion partially restored tumor growth. Furthermore, the growth of IL-5-secreting tumors was not impaired in either wild-type or IL-5(-/-) mice, even though it induced eosinophilia in both mouse strains. These findings demonstrate that eosinophils can be induced in IL-5(-/-) mice by exogenous IL-5 and argue against a compensatory effect of neutrophils in the absence of eosinophils. We conclude that 1) infiltration of IL-4 transfected tumors by eosinophils is completely IL-5 dependent, 2) eosinophils have no tumoricidal activity, and 3) neutrophils are responsible, at least in part, for tumor suppression.

Animals↗

PubMed1998

IL-6-deficient mice resist myelin oligodendrocyte glycoprotein-induced autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is induced by immunization with myelin components including myelin oligodendrocyte glycoprotein (MOG). Myelin-specific Th1 cells enter the central nervous system (CNS) via binding of very late antigen 4 (VLA-4) to the endothelial vascular cell adhesion molecule 1 (VCAM-1). In the present study, mice with a homologous disruption of the gene encoding IL-6 are found to be resistant to MOG-induced EAE as evidenced by absence of clinical symptoms, minimal infiltration of CD3+ T cells and monocytes into the CNS and lack of demyelination. The failure to induce EAE in IL-6-/- mice is not due to the absence of priming, since lymphocytes of immunized IL-6-/- mice proliferate in response to MOG and produce pro-inflammatory cytokines including IL-2 and IFN-gamma. However, in MOG-immunized IL-6-/- mice, serum anti-MOG antibody titers were found to be drastically reduced. This observation is unlikely to be responsible for resistance to EAE, because B cell-deficient (microMT) mice proved to be fully susceptible to the disease. A striking difference between MOG-immunized wild-type (wt) and IL-6-/- mice was the expression of endothelial VCAM-1 and ICAM-1, which were dramatically up-regulated in the CNS in wt but not in IL-6-/- mice. Taking into account recent studies on the role of VCAM-1 in the entry of Th1 cells into the CNS, the absence of VCAM-1 on endothelial cells in IL-6-/- mice may explain their resistance to EAE.

Animals↗

PubMed1998

Eosinophils are not required to induce airway hyperresponsiveness after nematode infection.

Eosinophilic inflammation of the airways is believed to play a central role in the pathogenesis of bronchial asthma. Inoculation of mice with the nematode Nippostrongylus brasiliensis induces pulmonary inflammation, characterized by a marked infiltration of eosinophils, subsequent to the migration of parasites through the lungs. Infection is associated with polarized Th2 responses in different strains of mice tested. Thus, this model may be useful to determine the relationship between established pulmonary eosinophilic inflammation, Th2 immune responses and airway changes in a nonallergic background. In the present study, we have used IL-5-deficient mice to evaluate the role of IL-5 in eosinophilic lung inflammation and airway hyperresponsiveness (AHR). In wild-type C57B/6 mice, infection with N. brasiliensis resulted in eosinophil accumulation, associated with extensive lung damage characterized by hemorrhage and alveolar wall destruction, and a strong AHR following methacholine treatment. In IL-5-deficient mice, eosinophil infiltration and the associated lung damage was abrogated. Nonetheless, AHR was unimpaired. Our results suggest that eosinophil accumulation plays a central role in lung damage but is not responsible for the induction of airway constriction following N. brasiliensis infection.

Animals↗

PubMed1998

Induction of gut mucosal immune responses: importance of genetic background and Th1/Th2 cross-regulation.

The reciprocal regulation of T-helper cell (Th) subsets is widely documented in various animal models of infectious diseases. In this study IFN-gamma/IL-4 double knockout (DKO) mice were used to analyse the role of Th subsets in mucosal immune responses. We found that the DKO mice had normal IgA differentiation but impaired induction of specific gut mucosal antibody responses after oral immunization using cholera toxin adjuvant. Both Th1 and Th2 responses were reduced compared with wild-type mice. Despite the absence of both IFN-gamma and IL-4 in the DKO mice the overall results were similar to previous observations in IFN-gamma receptor-knockout (IFN-gammaR-/-) mice and did not suggest a strict cross-regulation of the two Th subsets in the gut mucosa. To further examine the role of IFN-gamma in mucosal immunity we compared two different mouse strains lacking IFN-gamma, i.e. IFN-gamma-/- (C57BL/6) and IFN-gammaR-/- mice (129/Sv). We found that IFN-gammaR-/- mice exhibited reduced mucosal antibody responses and decreased Th1 and Th2 activity after oral immunization, while IFN-gamma-/- mice had intact antibody responses and increased Th2 responses. Thus, genetic differences were found to critically affect the development of a specific gut mucosal immune response. An enhanced Th2 activity in the Peyer's patches following oral immunization was associated with an ability to mount strong intestinal IgA immunity.

Animals↗