No abstract

Respiratory failure during Pneumocystis pneumonia is mainly a consequence of exaggerated inflammatory responses to the organism. Dendritic cells (DCs) are the most potent APCs in the lung and are key to the regulation of innate and adaptive immune responses. However, their participation in the inflammatory response directed against Pneumocystis infection has not been fully elucidated. Therefore, we studied the role of Pneumocystis carinii, as well as Saccharomyces cerevisiae, cell wall-derived β-glucans, in DC costimulatory molecule expression. We further studied the impact of β-glucans on subsequent T cell activation. Because cytokine secretion by DCs has recently been shown to be regulated by Fas ligand (FasL), its role in β-glucan activation of DCs was also investigated. β-Glucan-induced DC activation occurred in part through dectin-1 receptors. We demonstrated that DC activation by β-glucans elicits T cell activation and polarization into a Th1 patterned response, but with the conspicuous absence of IL-12. These observations differed from LPS-driven T cell polarization, suggesting that β-glucans and LPS signal DC activation through different mechanisms. We additionally determined that IL-1β and TNF-α secretion by β-glucan-stimulated DCs was partially regulated by Fas-FasL. This suggests that dysregulation of FasL could further enhance exuberant and prolonged cytokine production by DCs following DC-T cell interactions, further promoting lung inflammation typical of Pneumocystis pneumonia.

Objective. To study lymphocyte markers in rheumatoid arthritis (RA)-associated interstitial pneumonitis (IP) compared with idiopathic IP.Methods. Paraffin-embedded lung biopsy specimens from patients with RA (n ‫؍‬ 15) and from those without RA (n ‫؍‬ 16), all of whom had a diagnosis of either nonspecific IP or usual IP, were studied. Tissue sections from each patient were reviewed by a pathologist, who was blinded to the clinical data. Age and pulmonary function test results were similar in RA and non-RA patients. After high-temperature antigen unmasking, sections were incubated with mouse monoclonal antibodies directed against CD3, CD4, CD8, CD16, and CD20. All slides were coded, and digital images (100؋ magnification) of the entire tissue area were obtained. Staining was quantified using computerassisted image analysis.Results. Staining for CD4 was more prominent in patients with RA than in the non-RA comparison group (median 9.3 cells/mm 2 , interquartile range [IQR] 5.5-27.3 versus 0.6 cells/mm 2 , IQR 0.2-1.9; P ‫؍‬ 0.002). CD4؉ cell counts were increased in RA patients with nonspecific IP as well as in RA patients with usual IP, with no major difference between these groups. Results were similar for quantification of CD3 (P ‫؍‬ 0.012).

Pneumocystis carinii continues to cause severe pneumonia in immunocompromised patients. Surfactant protein D (SP-D), a lung collectin, markedly accumulates during P. carinii pneumonia and binds to glycoprotein A (gpA) on the surface of P. carinii, thereby enhancing interactions with alveolar macrophages. Herein, we report the structural basis of the interaction of SP-D with gpA. We demonstrate that natural SP-D binds to purified gpA in the presence of 2 mM calcium in a saturable, concentration-dependent manner, which is abolished by 10 mM ethylenediaminetetraacetic acid. Increasing concentrations of calcium under otherwise cation-free conditions significantly enhance SP-D binding to gpA, whereas manganese and magnesium cations have minimal effect. Maximal SP-D binding occurs at pH 7.4, with significant inhibition at pH 4. SP-D binding to gpA is also competitively inhibited by maltose>glucose>mannose>N-acetyl-glucosamine. Comparison of the binding of various natural and recombinant forms of SP-D to gpA reveals that the number of carbohydrate recognition domains (CRDs) in a given SP-D form determines the relative extent of binding to gpA. Maximal binding is observed with natural SP-D (dodecamers and higher order SP-D complexes) followed by recombinant dodecamers. In contrast, recombinant full-length trimers exhibit substantially less binding, which is similar to that observed with a recombinant truncated molecule consisting of the CRD and neck regions, and containing trimers of this portion of the molecule. Taken together, these findings strongly indicate that the CRD of SP-D mediates interaction with P. carinii gpA through its attached oligosaccharides and that the extent of SP-D binding to P. carinii is greatest with dodecamers and higher order forms of SP-D.