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

Alveolar Macrophage–mediated Killing of Pneumocystis carinii f. sp. muris Involves Molecular Recognition by the Dectin-1 β-Glucan Receptor

Innate immune mechanisms against Pneumocystis carinii, a frequent cause of pneumonia in immunocompromised individuals, are not well understood. Using both real time polymerase chain reaction as a measure of organism viability and fluorescent deconvolution microscopy, we show that nonopsonic phagocytosis of P. carinii by alveolar macrophages is mediated by the Dectin-1 β-glucan receptor and that the subsequent generation of hydrogen peroxide is involved in alveolar macrophage–mediated killing of P. carinii. The macrophage Dectin-1 β-glucan receptor colocalized with the P. carinii cyst wall. However, blockage of Dectin-1 with high concentrations of anti–Dectin-1 antibody inhibited binding and concomitant killing of P. carinii by alveolar macrophages. Furthermore, RAW 264.7 macrophages overexpressing Dectin-1 bound P. carinii at a higher level than control RAW cells. In the presence of Dectin-1 blockage, killing of opsonized P. carinii could be restored through FcγRII/III receptors. Opsonized P. carinii could also be efficiently killed in the presence of FcγRII/III receptor blockage through Dectin-1–mediated phagocytosis. We further show that Dectin-1 is required for P. carinii–induced macrophage inflammatory protein 2 production by alveolar macrophages. Taken together, these results show that nonopsonic phagocytosis and subsequent killing of P. carinii by alveolar macrophages is dependent upon recognition by the Dectin-1 β-glucan receptor

Pulmonary Immune Cell Trafficking Promotes Host Defense against Alcohol-Associated Klebsiella Pneumonia

The intestinal microbiota generates many different metabolites which are critical for the regulation of host signaling pathways. In fact, a wide-range of diseases are associated with increased levels of local or systemic microbe-derived metabolites. In contrast, certain bacterial metabolites, such as tryptophan metabolites, are known to contribute to both local and systemic homeostasis. Chronic alcohol consumption is accompanied by alterations to intestinal microbial communities, and their functional capacities. However, little is known about the role of alcohol-associated dysbiosis on host defense against bacterial pneumonia. Our previous work using fecal transplantation demonstrated that alcohol-associated intestinal dysbiosis, independent of ethanol consumption, increased susceptibility to Klebsiella pneumonia. Here, we demonstrate that intestinal microbiota treatments mitigate the increased risk of alcohol-associated pneumonia. Treatment with the microbial metabolite indole or with probiotics reduced pulmonary and extrapulmonary bacterial burden, restored immune responses, and improved cellular trafficking required for host defense. Protective effects were, in part, mediated by aryl hydrocarbon receptors (AhR), as inhibition of AhR diminished the protective effects. Thus, alcohol appears to impair the production/processing of tryptophan catabolites resulting in immune dysregulation and impaired cellular trafficking. These data support microbiota therapeutics as novel strategies to mitigate the increased risk for alcohol-associated bacterial pneumonia

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