CD4+ T cell–independent vaccination against Pneumocystis carinii in mice

Host defenses are profoundly compromised in HIV-infected hosts due to progressive depletion of CD4(+) T lymphocytes. Moreover, deficient CD4(+) T lymphocytes impair vaccination approaches to prevent opportunistic infection. Therefore, we investigated a CD4(+) T cell–independent vaccine approach to a prototypic AIDS-defining infection, Pneumocystis carinii (PC) pneumonia. Here, we demonstrate that bone marrow–derived dendritic cells (DCs) expressing the murine CD40 ligand, when pulsed ex vivo by PC antigen, elicited significant titers of anti-PC IgG in CD4-deficient mice. Vaccinated animals demonstrated significant protection from PC infection, and this protection was the result of an effective humoral response, since adoptive transfer of CD4-depleted splenocytes or serum conferred this protection to CD4-deficient mice. Western blot analysis of PC antigen revealed that DC-vaccinated, CD4-deficient mice predominantly reacted to a 55-kDa PC antigen. These studies show promise for advances in CD4-independent vaccination against HIV-related pathogens

Divergent roles of IL-23 and IL-12 in host defense against Klebsiella pneumoniae

Interleukin (IL)-23 is a heterodimeric cytokine that shares the identical p40 subunit as IL-12 but exhibits a unique p19 subunit similar to IL-12 p35. IL-12/23 p40, interferon γ (IFN-γ), and IL-17 are critical for host defense against Klebsiella pneumoniae. In vitro, K. pneumoniae–pulsed dendritic cell culture supernatants elicit T cell IL-17 production in a IL-23–dependent manner. However, the importance of IL-23 during in vivo pulmonary challenge is unknown. We show that IL-12/23 p40–deficient mice are exquisitely sensitive to intrapulmonary K. pneumoniae inoculation and that IL-23 p19−/−, IL-17R−/−, and IL-12 p35−/− mice also show increased susceptibility to infection. p40−/− mice fail to generate pulmonary IFN-γ, IL-17, or IL-17F responses to infection, whereas p35−/− mice show normal IL-17 and IL-17F induction but reduced IFN-γ. Lung IL-17 and IL-17F production in p19−/− mice was dramatically reduced, and this strain showed substantial mortality from a sublethal dose of bacteria (103 CFU), despite normal IFN-γ induction. Administration of IL-17 restored bacterial control in p19−/− mice and to a lesser degree in p40−/− mice, suggesting an additional host defense requirement for IFN-γ in this strain. Together, these data demonstrate independent requirements for IL-12 and IL-23 in pulmonary host defense against K. pneumoniae, the former of which is required for IFN-γ expression and the latter of which is required for IL-17 production

Regulation of Lung Immunity and Host Defense by the Intestinal Microbiota

Every year in the United States approximately 200,000 people die from pulmonary infections, such as influenza and pneumonia, or from lung disease that is exacerbated by pulmonary infection. In addition, respiratory diseases such as, asthma, affect 300 million people worldwide. Therefore, understanding the mechanistic basis for host defense against infection and regulation of immune processes involved in asthma are crucial for the development of novel therapeutic strategies. The identification, characterization, and manipulation of immune regulatory networks in the lung represents one of the biggest challenges in treatment of lung associated disease. Recent evidence suggests that the gastrointestinal (GI) microbiota plays a key role in immune adaptation and initiation in the GI tract as well as at other distal mucosal sites, such as the lung. This review explores the current research describing the role of the GI microbiota in the regulation of pulmonary immune responses. Specific focus is given to understanding how intestinal dysbiosis affects lung health

In Vitro Effector Activity of Pneumocystis murina-Specific T-Cytotoxic-1 CD8(+) T Cells: Role of Granulocyte-Macrophage Colony-Stimulating Factor

Human immunodeficiency virus (HIV)-related opportunistic infections continue to occur in patients who are newly diagnosed with HIV infection, those in the early course of highly active antiretroviral therapy or nonadherent to HIV care, and other immunosuppressed individuals. One of the most common opportunistic infections in these patients is Pneumocystis pneumonia. CD8(+) T cells are recruited to the lung after P. carinii infection and have been associated with both lung injury and host defense. This variability may be due to subpopulations of CD8(+) T cells recruited to the lung. We have previously shown using adoptive transfer studies that in vivo-generated T-cytotoxic-1 (Tc1) CD8(+) T cells, defined by the secretion of gamma interferon (IFN-γ), have effector activity against Pneumocystis spp. in vitro as well as in vivo. To better understand the mechanisms of these effects, we generated, expanded, and tested Tc1 and Tc2 CD8(+) T cells specific for P. murina ex vivo. Tc1-polarized CD8(+) T cells secreted higher levels of IFN-γ and granulocyte-macrophage colony-stimulating factor (GM-CSF) and lower levels of interleukin-4 (IL-4), IL-5, IL-10, and IL-13 than Tc2 CD8(+) T cells when stimulated with P. murina antigen. Moreover, Tc1 CD8(+) T cells demonstrated enhanced effector activity in a macrophage-mediated killing assay which was independent of cell contact. The augmentation in macrophage-mediated P. murina killing was significantly abrogated when GM-CSF was neutralized in the Tc1 CD8(+) T cells. These data support the possibility that antigen-specific GM-CSF secretion is critical for effector activity of P. murina-specific Tc1 CD8(+) T cells in vitro

Increased Host Resistance against Pneumocystis carinii Pneumonia in γδ T-Cell-Deficient Mice: Protective Role of Gamma Interferon and CD8(+) T Cells

Although a clear relationship between αβ T-cell receptor-positive (αβ-TCR(+)) CD4(+) T cells and susceptibility to Pneumocystis carinii infection exists, the role of other T-cell subsets is less clearly defined. Previous studies have shown that γδ-TCR(+) T cells infiltrate into the lung during P. carinii pneumonia. Therefore, the present study examined the role of γδ-TCR(+) T cells in host defense against P. carinii pneumonia. C57BL/6 (control) and B6.129P2-Tcrd(tm1Mom) (γδ-TCR(+) T-cell-deficient) mice were inoculated intratracheally with P. carinii. At specific time points, mice were sacrificed and analyzed for P. carinii burden, T-cell subsets, and cytokine levels in lung tissue. Analysis of P. carinii burden showed a more rapid and complete resolution of infection in γδ-TCR(+) T-cell-deficient mice than in C57BL/6 controls. This augmented resolution was associated with elevated gamma interferon (IFN-γ) levels in bronchoalveolar lavage fluid predominantly produced by CD8(+) T cells, as well as an increased recruitment of CD8(+) T cells in general. In separate experiments, neutralization of IFN-γ or depletion of CD8(+) T cells early during infection abolished the augmented resolution previously observed in γδ-TCR(+) T-cell-deficient mice. These results show that the presence of γδ-TCR(+) T cells modulates host susceptibility to P. carinii pneumonia through interactions with pulmonary CD8(+) T cells and tissue production of IFN-γ

Local Delivery of the Viral Interleukin-10 Gene Suppresses Tissue Inflammation in Murine Pneumocystis carinii Infection

The relationship between tissue inflammation and clearance of the opportunistic pathogen Pneumocystis carinii is poorly understood. We asked whether the anti-inflammatory cytokine interleukin-10 (IL-10) is released during the host response to infection with P. carinii and whether local delivery of the IL-10 gene could suppress tissue inflammatory responses without compromising clearance of infection. Control and CD4-depleted mice were inoculated with P. carinii, and at serial intervals after inoculation, lung tissue was assayed for IL-10 by enzyme-linked immunosorbent assay. We found that IL-10 was released in lung tissue in control mice and was present in higher concentrations in CD4-depleted mice with progressive infection. Control and CD4-depleted mice were then pretreated with 10(9) PFU of intratracheally administered adenoviral vector containing the viral IL-10 gene or the luciferase gene followed by inoculation with P. carinii. Pretreatment with viral IL-10 did not alter clearance of infection in control mice or severity of infection in CD4-depleted mice but did decrease tissue inflammation. We then asked whether gene transfer of viral IL-10 could decrease tissue inflammation during immune reconstitution. In these experiments, immunodeficient scid mice were inoculated with P. carinii and were heavily infected after 4 weeks. When these mice are immunologically reconstituted by intravenous administration of spleen cells from normal mice, a hyperinflammatory reaction developed in lung tissue, associated with high mortality. In comparison to control mice, mice treated with viral IL-10 prior to reconstitution showed significantly decreased lung wet weight, bronchoalveolar lavage fluid (BALF) lactate dehydrogenase, and BALF neutrophils. In contrast, infection intensity, as measured by PCR for P. carinii rRNA, was unchanged between the IL-10 and luciferase groups. Survival was also improved in the IL-10-treated mice. We conclude that release of IL-10 is part of the host response to infection with P. carinii and that gene therapy with viral IL-10 can lessen excessive tissue inflammation without altering pathogen clearance. In the setting of immune reconstitution and P. carinii pneumonia, pretreatment with the viral IL-10 gene decreases excessive tissue inflammation and improves survival. These results are relevant to acute respiratory failure after initiation of antibiotic treatment for human P. carinii pneumonia and to immune reconstitution syndromes in human immunodeficiency virus-positive patients started on highly active antiretroviral therapy