TNF receptor signaling contributes to chemokine secretion, inflammation, and respiratory deficits during Pneumocystis pneumonia

CD8(+) T cells contribute to the pathophysiology of Pneumocystis pneumonia (PcP) in a murine model of AIDS-related disease. The present studies were undertaken to more precisely define the mechanisms by which these immune cells mediate the inflammatory response that leads to lung injury. Experimental mice were depleted of either CD4(+) T cells or both CD4(+) and CD8(+) T cells and then infected with Pneumocystis: The CD4(+)-depleted mice had significantly greater pulmonary TNF-alpha levels than mice depleted of both CD4(+) and CD8(+) T cells. Elevated TNF-alpha levels were associated with increased lung concentrations of the chemokines RANTES, monocyte chemoattractant protein 1, macrophage-inflammatory protein 2, and cytokine-induced neutrophil chemoattractant. To determine whether TNFR signaling was involved in the CD8(+) T cell-dependent chemokine response, TNFRI- and II-deficient mice were CD4(+) depleted and infected with Pneumocystis: TNFR-deficient mice had significantly reduced pulmonary RANTES, monocyte chemoattractant protein 1, macrophage-inflammatory protein 2, and cytokine-induced neutrophil chemoattractant responses, reduced inflammatory cell recruitment to the alveoli, and reduced histological evidence of PcP-related alveolitis as compared with infected wild-type mice. Diminished pulmonary inflammation correlated with improved surfactant activity and improved pulmonary function in the TNFR-deficient mice. These data indicate that TNFR signaling is required for maximal CD8(+) T cell-dependent pulmonary inflammation and lung injury during PcP and also demonstrate that CD8(+) T cells can use TNFR signaling pathways to respond to an extracellular fungal pathogen.     

Parenchymal cell TNF receptors contribute to inflammatory cell recruitment and respiratory failure in Pneumocystis carinii-induced pneumonia

The opportunistic organism Pneumocystis carinii (Pc) produces a life-threatening pneumonia (PcP) in patients with low CD4(+) T cell counts. Animal models of HIV-AIDS-related PcP indicate that development of severe disease is dependent on the presence of CD8(+) T cells and the TNF receptors (TNFR) TNFRsf1a and TNFRsf1b. To distinguish roles of parenchymal and hematopoietic cell TNF signaling in PcP-related lung injury, murine bone marrow transplant chimeras of wild-type, C57BL6/J, and TNFRsf1a/1b double-null origin were generated, CD4(+) T cell depleted, and inoculated with Pc. As expected, C57 --> C57 chimeras (donor marrow --> recipient) developed significant disease as assessed by weight loss, impaired pulmonary function (lung resistance and dynamic lung compliance), and inflammatory cell infiltration. In contrast, TNFRsf1a/1b(-/-) --> TNFRsf1a/1b(-/-) mice were relatively mildly affected despite carrying the greatest organism burden. Mice solely lacking parenchymal TNFRs (C57 --> TNFRsf1a/1b(-/-)) had milder disease than did C57 --> C57 mice. Both groups of mice with TNFR-deficient parenchymal cells had low bronchoalveolar lavage fluid total cell counts and fewer lavageable CD8(+) T cells than did C57 --> C57 mice, suggesting that parenchymal TNFR signaling contributes to PcP-related immunopathology through the recruitment of damaging immune cells. Interestingly, mice with wild-type parenchymal cells but TNFRsf1a/1b(-/-) hematopoietic cells (TNFRsf1a/1b(-/-) --> C57) displayed exacerbated disease characterized by increased MCP-1 and KC production in the lung and increased macrophage and lymphocyte numbers in the lavage, indicating a dysregulated immune response. This study supports a key role of parenchymal cell TNFRs in lung injury induced by Pc and a potential protective effect of receptors on radiosensitive, bone marrow-derived cells.     

Multiple CD4+ T cell subsets produce immunomodulatory IL-10 during respiratory syncytial virus infection

The host immune response is believed to contribute to the severity of pulmonary disease induced by acute respiratory syncytial virus (RSV) infection. Because RSV-induced pulmonary disease is associated with immunopathology, we evaluated the role of IL-10 in modulating the RSV-specific immune response. We found that IL-10 protein levels in the lung were increased following acute RSV infection, with maximum production corresponding to the peak of the virus-specific T cell response. The majority of IL-10-producing cells in the lung during acute RSV infection were CD4(+) T cells. The IL-10-producing CD4(+) T cells included Foxp3(+) regulatory T cells, Foxp3(-) CD4(+) T cells that coproduce IFN-γ, and Foxp3(-) CD4(+) T cells that do not coproduce IFN-γ. RSV infection of IL-10-deficient mice resulted in more severe disease, as measured by increased weight loss and airway resistance, as compared with control mice. We also observed an increase in the magnitude of the RSV-induced CD8(+) and CD4(+) T cell response that correlated with increased disease severity in the absence of IL-10 or following IL-10R blockade. Interestingly, IL-10R blockade during acute RSV infection altered CD4(+) T cell subset distribution, resulting in a significant increase in IL-17A-producing CD4(+) T cells and a concomitant decrease in Foxp3(+) regulatory T cells. These results demonstrate that IL-10 plays a critical role in modulating the adaptive immune response to RSV by limiting T-cell-mediated pulmonary inflammation and injury.     

Antibody-independent antiviral function of memory CD4+ T cells in vivo requires regulatory signals from CD8+ effector T cells

Previous studies have shown that vaccine-primed CD4(+) T cells can mediate accelerated clearance of respiratory virus infection. However, the relative contributions of Ab and CD8(+) T cells, and the mechanism of viral clearance, are poorly understood. Here we show that control of a Sendai virus infection by primed CD4(+) T cells is mediated through the production of IFN-gamma and does not depend on Ab. This effect is critically dependent on CD8(+) cells for the expansion of CD4(+) T cells in the lymph nodes and the recruitment of memory CD4(+) T cells to the lungs. Passive transfer of a CD8(+) T cell supernatant into CD8(+) T cell-depleted, hemagglutinin-neuraminidase (HN)(421-436)-immune muMT mice substantially restored the virus-specific memory CD4(+) response and enhanced viral control in the lung. Together, the data demonstrate for the first time that in vivo primed CD4(+) T cells have the capacity to control a respiratory virus infection in the lung by an Ab-independent mechanism, provided that CD8(+) T cell "help" in the form of soluble factor(s) is available during the virus infection. These studies highlight the importance of synergistic interactions between CD4(+) and CD8(+) T cell subsets in the generation of optimal antiviral immunity.     

CD4(+) T cells are required for the development of cytotoxic CD8(+) T cells during Mycobacterium tuberculosis infection.

The control of acute and chronic Mycobacterium tuberculosis infection is dependent on CD4(+) T cells. In a variety of systems CD8(+) T cell effector responses are dependent on CD4(+) T cell help. The development of CD8(+) T cell-mediated immune responses in the absence of CD4(+) T cells was investigated in a murine model of acute tuberculosis. In vitro and in vivo, priming of mycobacteria-specific CD8(+) T cells was unaffected by the absence of CD4(+) T cells. Infiltration of CD8(+) T cells into infected lungs of CD4(-/-) or wild-type mice was similar. IFN-gamma production by lung CD8(+) T cells in CD4(-/-) and wild-type mice was also comparable, suggesting that emergence of IFN-gamma-producing mycobacteria-specific CD8(+) T cells in the lungs was independent of CD4(+) T cell help. In contrast, cytotoxic activity of CD8(+) T cells from lungs of M. tuberculosis-infected mice was impaired in CD4(-/-) mice. Expression of mRNA for IL-2 and IL-15, cytokines critical for the development of cytotoxic effector cells, was diminished in the lungs of M. tuberculosis-infected CD4(-/-) mice. As tuberculosis is frequently associated with HIV infection and a subsequent loss of CD4(+) T cells, understanding the interaction between CD4(+) and CD8(+) T cell subsets during the immune response to M. tuberculosis is imperative for the design of successful vaccination strategies.     

Efficient lung recruitment of respiratory syncytial virus-specific Th1 cells induced by recombinant bacillus Calmette-Guérin promotes virus clearance and protects from infection

Infection by the respiratory syncytial virus (RSV) can cause extensive inflammation and lung damage in susceptible hosts due to a Th2-biased immune response. Such a deleterious inflammatory response can be enhanced by immunization with formalin- or UV-inactivated RSV, as well as with vaccinia virus expressing the RSV-G protein. Recently, we have shown that vaccination with rBCG-expressing RSV Ags can prevent the disease in the mouse. To further understand the immunological mechanisms responsible for protection against RSV, we have characterized the T cell populations contributing to virus clearance in mice immunized with this BCG-based vaccine. We found that both CD4(+) and CD8(+) T cells were recruited significantly earlier to the lungs of infected mice that were previously vaccinated. Furthermore, we observed that simultaneous adoptive transfer of CD8(+) and CD4(+) RSV-specific T cells from vaccinated mice was required to confer protection against virus infection in naive recipients. In addition, CD4(+) T cells induced by vaccination released IFN-γ after RSV challenge, indicating that protection is mediated by a Th1 immune response. These data suggest that vaccination with rBCG-expressing RSV Ags can induce a specific effector/memory Th1 immune response consisting on CD4(+) and CD8(+) T cells, both necessary for a fully protective response against RSV. These results support the notion that an effective induction of Th1 T cell immunity against RSV during childhood could counteract the unbalanced Th2-like immune response triggered by the natural RSV infection.     

Human CD8⁺ and CD4⁺ T cell memory to lymphocytic choriomeningitis virus infection

Although cellular immunity to acute lymphocytic choriomeningitis virus (LCMV) infection has been well characterized in experimental studies in mice, the T cell response to this virus in humans is incompletely understood. Thus, we analyzed the breadths, magnitudes, and differentiation phenotypes of memory LCMV-specific CD8(+) and CD4(+) T cells in three human donors displaying a variety of disease outcomes after accidental needle stick injury or exposure to LCMV. Although only a small cohort of donors was analyzed at a single time point postinfection, several interesting observations were made. First, we were able to detect LCMV-specific CD8(+) and CD4(+) T cell responses directly ex vivo at 4 to 8 years after exposure, demonstrating the longevity of T cell memory in humans. Second, unlike in murine models of LCMV infection, we found that the breadths of memory CD8(+) and CD4(+) T cell responses were not significantly different from one another. Third, it seemed that the overall CD8(+) T cell response was augmented with increasing severity of disease, while the LCMV-specific CD4(+) T cell response magnitude was highly variable between the three different donors. Next, we found that LCMV-specific CD8(+) T cells in the three donors analyzed seemed to undergo an effector memory differentiation program distinct from that of CD4(+) T cells. Finally, the levels of expression of memory, costimulatory, and inhibitory receptors on CD8(+) and CD4(+) T cell subsets, in some instances, correlated with disease outcome. These data demonstrate for the first time LCMV-specific CD8(+) and CD4(+) T cells in infected humans and begin to provide new insights into memory T cell responses following an acute virus infection.     

A transgenic model of central nervous system autoimmunity mediated by CD4+ and CD8+ T and B cells

Experimental autoimmune encephalomyelitis (EAE) is a widely used model of multiple sclerosis. In NOD mice, EAE develops as a relapsing-remitting disease that transitions to a chronic progressive disease, making the NOD model the only mouse model that recapitulates the full clinical disease course observed in most multiple sclerosis patients. We have generated a TCR transgenic mouse that expresses the α- and β-chains of a myelin oligodendrocyte glycoprotein (MOG) 35-55-reactive TCR (1C6) on the NOD background. 1C6 TCR transgenic mice spontaneously generate both CD4(+) and CD8(+) T cells that recognize MOG and produce proinflammatory cytokines, allowing for the first time to our knowledge the simultaneous examination of myelin-reactive CD4(+) and CD8(+) T cells in the same host. 1C6 CD8(+) T cells alone can induce optic neuritis and mild EAE with delayed onset; however, 1C6 CD4(+) T cells alone induce severe EAE and predominate in driving disease when both cell types are present. When 1C6 mice are crossed with mice bearing an IgH specific for MOG, the mice develop spontaneous EAE with high incidence, but surprisingly the disease pattern does not resemble the neuromyelitis optica-like disease observed in mice bearing CD4(+) T cells and B cells reactive to MOG on the C57BL/6 background. Collectively, our data show that although myelin-reactive CD8(+) T cells contribute to disease, disease is primarily driven by myelin-reactive CD4(+) T cells and that the coexistence of myelin-reactive T and B cells does not necessarily result in a distinct pathological phenotype.     

Aged Mice Exhibit a Severely Diminished CD8 T Cell Response following Respiratory Syncytial Virus Infection

Respiratory virus infections in the elderly result in increased rates of hospitalization and death. Respiratory syncytial virus (RSV) is a leading cause of severe virus-induced respiratory disease in individuals over the age of 65. CD8 T cells play a critical role in mediating RSV clearance. While it is clear that T cell immunity declines with age, it is not clear to what extent the CD8 T cell response to RSV is altered. Using aged BALB/c mice, we demonstrated that RSV-specific CD8 T cell responses were significantly reduced in the lungs of aged mice at the peak of the T cell response and that this decrease correlated with delayed viral clearance. Despite a decrease in the overall numbers of RSV-specific CD8 T cells during acute infection, their capacity to produce effector cytokines was not impaired. Following viral clearance, the RSV-specific memory CD8 T cells were similar in total number and phenotype in young and aged mice. Furthermore, following infection with a heterologous pathogen expressing an RSV epitope, RSV-specific memory CD8 T cells exhibited similar activation and ability to provide early control of the infection in young and aged mice. These data demonstrate a decrease in the capacity of aged mice to induce a high-magnitude acute CD8 T cell response, leading to prolonged viral replication, which may contribute to the increased disease severity of RSV infection observed for aged individuals.     

CD4+ T cell-associated pathophysiology critically depends on CD18 gene dose effects in a murine model of psoriasis

In a CD18 hypomorphic polygenic PL/J mouse model, the severe reduction of CD18 (beta(2) integrin) to 2-16% of wild-type levels leads to the development of a psoriasiform skin disease. In this study, we analyzed the influence of reduced CD18 gene expression on T cell function, and its contribution to the pathogenesis of this disease. Both CD4(+) and CD8(+) T cells were significantly increased in the skin of affected CD18 hypomorphic mice. But only depletion of CD4(+) T cells, and not the removal of CD8(+) T cells, resulted in a complete clearance of the psoriasiform dermatitis. This indicates a central role of CD4(+) T cells in the pathogenesis of this disorder, further supported by the detection of several Th1-like cytokines released predominantly by CD4(+) T cells. In contrast to the CD18 hypomorphic mice, CD18 null mutants of the same strain did not develop the psoriasiform dermatitis. This is in part due to a lack of T cell emigration from dermal blood vessels, as experimental allergic contact dermatitis could be induced in CD18 hypomorphic and wild-type mice, but not in CD18 null mutants. Hence, 2-16% of CD18 gene expression is obviously sufficient for T cell emigration driving the inflammatory phenotype in CD18 hypomorphic mice. Our data suggest that the pathogenic involvement of CD4(+) T cells depends on a gene dose effect with a reduced expression of the CD18 protein in PL/J mice. This murine inflammatory skin model may also have relevance for human polygenic inflammatory diseases.     

The antiviral CD8+ T cell response is differentially dependent on CD4+ T cell help over the course of persistent infection

Although many studies have investigated the requirement for CD4(+) T cell help for CD8(+) T cell responses to acute viral infections that are fully resolved, less is known about the role of CD4(+) T cells in maintaining ongoing CD8(+) T cell responses to persistently infecting viruses. Using mouse polyoma virus (PyV), we asked whether CD4(+) T cell help is required to maintain antiviral CD8(+) T cell and humoral responses during acute and persistent phases of infection. Though fully intact during acute infection, the PyV-specific CD8(+) T cell response declined numerically during persistent infection in MHC class II-deficient mice, leaving a small antiviral CD8(+) T cell population that was maintained long term. These unhelped PyV-specific CD8(+) T cells were functionally unimpaired; they retained the potential for robust expansion and cytokine production in response to Ag rechallenge. In addition, although a strong antiviral IgG response was initially elicited by MHC class II-deficient mice, these Ab titers fell, and long-lived PyV-specific Ab-secreting cells were not detected in the bone marrow. Finally, using a minimally myeloablative mixed bone marrow chimerism approach, we demonstrate that recruitment and/or maintenance of new virus-specific CD8(+) T cells during persistent infection is impaired in the absence of MHC class II-restricted T cells. In summary, these studies show that CD4(+) T cells differentially affect CD8(+) T cell responses over the course of a persistent virus infection.     

A recombinant Sendai virus is controlled by CD4+ effector T cells responding to a secreted human immunodeficiency virus type 1 envelope glycoprotein

The importance of antigen-specific CD4(+) helper T cells in virus infections is well recognized, but their possible role as direct mediators of virus clearance is less well characterized. Here we describe a recombinant Sendai virus strategy for probing the effector role(s) of CD4(+) T cells. Mice were vaccinated with DNA and vaccinia virus recombinant vectors encoding a secreted human immunodeficiency virus type 1 (HIV-1) envelope protein and then challenged with a Sendai virus carrying a homologous HIV-1 envelope gene. The primed mice showed (i) prompt homing of numerous envelope-primed CD4(+) T cell populations to the virus-infected lung, (ii) substantial production of gamma interferon, and interleukin-2 (IL-2), IL-4, and IL-5 in that site, and (iii) significantly reduced pulmonary viral load. The challenge experiments were repeated with immunoglobulin(-/-) microMT mice in the presence or absence of CD8(+) and/or CD4(+) T cells. These selectively immunodeficient mice were protected by primed CD4(+) T cells in the absence of antibody or CD8(+) T cells. Together, these results highlight the role of CD4(+) T cells as direct effectors in vivo and, because this protocol gives such a potent response, identify an outstanding experimental model for further dissecting CD4(+) T-cell-mediated immunity in the lung.     

Diminished primary and secondary influenza virus-specific CD8(+) T-cell responses in CD4-depleted Ig(-/-) mice

Optimal expansion of influenza virus nucleoprotein (D(b)NP(366))-specific CD8(+) T cells following respiratory challenge of naive Ig(-/-) microMT mice was found to require CD4(+) T-cell help, and this effect was also observed in primed animals. Absence of the CD4(+) population was consistently correlated with diminished recruitment of virus-specific CD8(+) T cells to the infected lung, delayed virus clearance, and increased morbidity. The splenic CD8(+) set generated during the recall response in Ig(-/-) mice primed at least 6 months previously showed a normal profile of gamma interferon production subsequent to short-term, in vitro stimulation with viral peptide, irrespective of a concurrent CD4(+) T-cell response. Both the magnitude and the localization profiles of virus-specific CD8(+) T cells, though perhaps not their functional characteristics, are thus modified in mice lacking CD4(+) T cells.     

T cytotoxic-1 CD8+ T cells are effector cells against pneumocystis in mice

Host defenses are profoundly compromised in HIV-infected hosts due to progressive depletion of CD4+ T lymphocytes. A hallmark of HIV infection is Pneumocystis carinii (PC) pneumonia. Recently, CD8+ T cells, which are recruited to the lung in large numbers in response to PC infection, have been associated with some level of host defense as well as contributing to lung injury in BALB/c mice. In this study, we show that CD8+ T cells that have a T cytotoxic-1 response to PC in BALB/c mice, as determined by secretion of IFN-gamma, have in vitro killing activity against PC and effect clearance of the organism in adoptive transfer studies. Moreover, non-T cytotoxic-1 CD8+ T cells lacked in vitro effector activity and contributed to lung injury upon adoptive transfer. This dichotomous response in CD8+ T cell response may in part explain the clinical heterogeneity in the severity of PC pneumonia.     

An MHC class Ib-restricted CD8+ T cell response to lymphocytic choriomeningitis virus

Conventional MHC class Ia-restricted CD8(+) T cells play a dominant role in the host response to virus infections, but recent studies indicate that T cells with specificity for nonclassical MHC class Ib molecules may also participate in host defense. To investigate the potential role of class Ib molecules in anti-viral immune responses, K(b-/-)D(b-/-)CIITA(-/-) mice lacking expression of MHC class Ia and class II molecules were infected with lymphocytic choriomeningitis virus (LCMV). These animals have a large class Ib-selected CD8(+) T cell population and they were observed to mediate partial (but incomplete) virus clearance during acute LCMV infection as compared with K(b-/-)D(b-/-)β(2)-microglobulin(-/-) mice that lack expression of both MHC class Ia and class Ib molecules. Infection was associated with expansion of splenic CD8(+) T cells and induction of granzyme B and IFN-γ effector molecules in CD8(+) T cells. Partial virus clearance was dependent on CD8(+) cells. In vitro T cell restimulation assays demonstrated induction of a population of β(2)-microglobulin-dependent, MHC class Ib-restricted CD8(+) T cells with specificity for viral Ags and yet to be defined nonclassical MHC molecules. MHC class Ib-restricted CD8(+) T cell responses were also observed after infection of K(b-/-)D(b-/-)mice despite the low number of CD8(+) T cells in these animals. Long-term infection studies demonstrated chronic infection and gradual depletion of CD8(+) T cells in K(b-/-)D(b-/-)CIITA(-/-) mice, demonstrating that class Ia molecules are required for viral clearance. These findings demonstrate that class Ib-restricted CD8(+) T cells have the potential to participate in the host immune response to LCMV.     

T cell TRAIL promotes murine lupus by sustaining effector CD4 Th cell numbers and by inhibiting CD8 CTL activity

T cells play an essential role in driving humoral autoimmunity in lupus. Molecules such as TRAIL exhibit strong T cell modulatory effects and are up-regulated in lupus, raising the possibility that they may influence disease severity. To address this possibility, we examined the role of TRAIL expression on pathogenic T cells in an induced model of murine lupus, the parent-into-F(1) (P-->F(1)) model of chronic graft-vs-host disease (GVHD), using wild-type or TRAIL-deficient donor T cells. Results were compared with mice undergoing suppressive acute GVHD. Although chronic GVHD mice exhibited less donor T cell TRAIL up-regulation and IFN-alpha-inducible gene expression than acute GVHD mice, donor CD4(+) T cell TRAIL expression in chronic GVHD was essential for sustaining effector CD4(+) Th cell numbers, for sustaining help to B cells, and for more severe lupus-like renal disease development. Conversely, TRAIL expression on donor CD8(+) T cells had a milder, but significant down-regulatory effect on CTL effector function, affecting the perforin/granzyme pathway and not the Fas ligand pathway. These results indicate that, in this model, T cell-expressed TRAIL exacerbates lupus by the following: 1) positively regulating CD4(+) Th cell numbers, thereby sustaining T cell help for B cells, and 2) to a lesser degree by negatively regulating perforin-mediated CD8(+) CTL killing that could potentially eliminate activated autoreactive B cells.     

Cellular and humoral immunity against vaccinia virus infection of mice

Despite the widespread use of vaccinia virus (VV) as a vector for other Ags and as the smallpox vaccine, there is little information available about the protective components of the immune response following VV infection. In this study, protection against wild-type VV was evaluated in mice with respect to the relative contributions of CD8(+) T cells vs that of CD4(+) T cells and Ab. C57BL/6 mice primed with the Western Reserve strain of VV mount significant IgM and IgG Ab responses, specific cytotoxic T cell responses, IFN-gamma responses in CD4(+) and CD8(+) T cells, and effectively clear the virus. This protection was abrogated by in vivo depletion of CD4(+) T cells or B cells in IgH(-/-) mice, but was not sensitive to CD8(+) T cell depletion alone. However, a role for CD8(+) T cells in primary protection was demonstrated in MHC class II(-/-) mice, where depleting CD8(+) T cells lead to increase severity of disease. Unlike control MHC class II(-/-) mice, the group depleted of CD8(+) T cells developed skin lesions on the tail and feet and had adrenal necrosis. Adoptive transfer experiments also show CD8(+) T cells can mediate protective memory. These results collectively show that both CD4(+) and CD8(+) T cell-mediated immunity can contribute to protection against VV infection. However, CD4(+) T cell-dependent anti-virus Ab production plays a more important role in clearing virus following acute infection, while in the absence of Ab, CD8(+) T cells can contribute to protection against disease.     

CXCR3 and IFN protein-10 in Pneumocystis pneumonia

We have previously shown that Tc1 CD8(+) T cells have in vitro and in vivo effector activity against Pneumocystis (PC) infection in mice. Because these cells have preferential expression of CXCR3, we investigated whether CXCR3 was required for host defense activity against PC. Mice deficient in CXCR3 but CD4(+) T cell intact, showed an initial delay but were able to clear the infectious challenge, indicating that CXCR3 signaling is not essential for clearance of PC. CD4-depleted mice had lower levels of monokine induced by IFN-gamma, IFN protein-10 (IP-10), and IFN-inducible T cell alpha-chemoattractant at day 7 of infection and are permissive to PC infection. Overexpression of IP-10 in the lungs by adenoviral gene transfer did not accelerate clearance of infection in control mice but accelerated clearance by day 28 in mice depleted of CD4(+) T cells. This effect was associated with increased recruitment of CD8(+) T to the lungs with higher CXCR3(+) expression levels and enhanced IFN-gamma secretion upon in vitro activation compared with control mice. These results indicate that the CXCR3 chemokines are part of the host defense response to PC, and that IP-10 can direct Tc1 CD8(+) T cell recruitment to the lungs and contribute to host defense against PC even in the absence of CD4(+) T cells.     

IL-10 modulates host responses and lung damage induced by Pneumocystis carinii infection

Host responses to Pneumocystis carinii infection mediate impairment of pulmonary function and contribute to the pathogenesis of pneumonia. IL-10 is known to inhibit inflammation and reduce the severity of pathology caused by a number of infectious organisms. In the present studies, IL-10-deficient (IL-10 knockout (KO)) mice were infected with P. carinii to determine whether the severity of pathogenesis and the efficiency of clearance of the organisms could be altered in the absence of IL-10. The clearance kinetics of P. carinii from IL-10 KO mice was significantly enhanced compared with that of wild-type (WT) mice. This corresponded to a more intense CD4(+) and CD8(+) T cell response as well as an earlier neutrophil response in the lungs of IL-10 KO mice. Furthermore, IL-12, IL-18, and IFN-gamma were found in the bronchoalveolar lavage fluids at earlier time points in IL-10 KO mice suggesting that alveolar macrophages were activated earlier than in WT mice. However, when CD4(+) cells were depleted from P. carinii-infected IL-10 KO mice, the ability to enhance clearance was lost. Furthermore, CD4-depleted IL-10 KO mice had significantly more lung injury than CD4-depleted WT mice even though the intensity of the inflammatory responses was similar. This was characterized by increased vascular leakage, decreased oxygenation, and decreased arterial pH. These data indicate that IL-10 down-regulates the immune response to P. carinii in WT mice; however, in the absence of CD4(+) T cells, IL-10 plays a critical role in controlling lung damage independent of modulating the inflammatory response.     

Enhanced neointima formation following arterial injury in immune deficient Rag-1-/- mice is attenuated by adoptive transfer of CD8 T cells

T cells modulate neointima formation after arterial injury but the specific T cell population that is activated in response to arterial injury remains unknown. The objective of the study was to identify the T cell populations that are activated and modulate neointimal thickening after arterial injury in mice. Arterial injury in wild type C57Bl6 mice resulted in T cell activation characterized by increased CD4(+)CD44(hi) and CD8(+)CD44(hi) T cells in the lymph nodes and spleens. Splenic CD8(+)CD25(+) T cells and CD8(+)CD28(+) T cells, but not CD4(+)CD25(+) and CD4(+)CD28(+) T cells, were also significantly increased. Adoptive cell transfer of CD4(+) or CD8(+) T cells from donor CD8-/- or CD4-/- mice, respectively, to immune-deficient Rag-1-/- mice was performed to determine the T cell subtype that inhibits neointima formation after arterial injury. Rag-1-/- mice that received CD8(+) T cells had significantly reduced neointima formation compared with Rag-1-/- mice without cell transfer. CD4(+) T cell transfer did not reduce neointima formation. CD8(+) T cells from CD4-/- mice had cytotoxic activity against syngeneic smooth muscle cells in vitro. The study shows that although both CD8(+) T cells and CD4(+) T cells are activated in response to arterial injury, adoptive cell transfer identifies CD8(+) T cells as the specific and selective cell type involved in inhibiting neointima formation.