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In 328 immunocompromised patients, 105 with and 193 without Pneumocystis jiroveci pneumonia (PCP), serum lactate dehydrogenase (LDH) was analysed retrospectively, taking into consideration the time interval from the onset of symptoms to the start of specific therapy. 97 of the 105 PCP patients were negative for human immunodeficiency virus (HIV). Eight were positive. Of the 193 patients without PCP 134 were HIV-negative and 59 were HIV-positive. In HIV-negative patients the sensitivity of LDH elevation was 63% and specificity 43%. In HIV-positive patients sensitivity was 100% and specificity 47%. The overall accuracy of LDH for the diagnosis of PCP was 52%, 51% in HIV-negative and 58% in HIV-positive patients. Except for its sensitivity in HIV-positive patients, the value of LDH for the diagnosis of PCP should not be overestimated.

Oxygen-dependent antimicrobial activity of human polymorphonuclear leukocytes (PMNs) relies on the phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase to generate oxidants. As the oxidase transfers electrons from NADPH the membrane will depolarize and concomitantly terminate oxidase activity, unless there is charge translocation to compensate. Most experimental data implicate proton channels as the effectors of this charge compensation, although large-conductance Ca 2؉ -activated K ؉ (BK) channels have been suggested to be essential for normal PMN antimicrobial activity. To test this latter notion, we directly assessed the role of BK channels in phagocyte function, including the NADPH oxidase. PMNs genetically lacking BK channels (BK ؊/؊ ) had normal intracellular and extracellular NADPH oxidase activity in response to both receptor-independent and phagocytic challenges. Furthermore, NADPH oxidase activity of human PMNs and macrophages was normal after treatment with BK channel inhibitors. Although BK channel inhibitors suppressed endotoxin-mediated tumor necrosis factor-␣ secretion by bone marrowderived macrophages (BMDMs), BMDMs of BK ؊/؊ and wild-type mice responded identically and exhibited the same ERK, PI3K/Akt, and nuclear factor-B activation. Based on these data, we conclude that the BK channel is not required for NADPH oxidase activity in PMNs or macrophages or for endotoxin-triggered tumor necrosis factor-␣ release and signal transduction BMDMs. IntroductionMany important compositional, physiologic, and biochemical features of the polymorphonuclear leukocyte (PMN) oxidase are now understood. 1 Assembled and active at the membrane of the cell surface or phagosome, the phagocyte oxidase operates as an electron transferase, shuttling electrons from cytoplasmic nicotinamide adenine dinucleotide phosphate (NADPH) across the membrane to oxygen, which is reduced to superoxide anion, the proximal product of the active enzyme. 2 Uncompensated, the directional electron flow would eventually depolarize the membrane to the equilibrium potential of electron transfer and prematurely terminate oxidase activity and superoxide anion generation. Evidence indicates that voltage-gated proton channels compensate most, if not all, of the charge and thus support continued oxidase activity. 3 An alternative mechanism for these events has been proposed, whereby a flux of K ϩ into the phagosome mediates charge compensation for oxidase-triggered electron flow, raises the pH of phagosome, and triggers the release of cationic granule proteases. 4 According to this model, K ϩ flux is mediated through the large conductance Ca ϩϩ -activated K ϩ channels (BK channel), and there is no role for proton channels, as the authors reported that Zn ϩϩ , at concentrations in excess of those that nearly completely block proton channel activity, 5 did not inhibit phagocyte oxidase activity. 6 We reasoned that, if BK channels contributed a functionally significant compensatory force during phagocyte oxidase activation, then the...

Legionella pneumophila, the causative agent of Legionnaires' disease, is able to survive and multiply efficiently in a variety of mammalian cells. By using in vitro assays, the uptake of L. pneumophila into monocytes has shown to be mediated, at least in part, through attachment of complement-coated bacteria to complement receptors, but complement-independent phagocytosis could also be demonstrated. Since complement levels in the human lung are normally low, the role of complement-dependent phagocytosis in the pathogenesis of Legionnaires' disease is doubtful. However, the contribution of other potential phagocytosis-related host cell surface molecules to the phagocytosis of L. pneumophila has never been investigated. We therefore analyzed the role of complement receptors 1 (CD35) and 3 (CD11b/18), the lipopolysaccharide (LPS) receptor (CD14), the L 1 -integrin chain of the fibronectin receptor (CD29), the intercellular adhesion molecule 1 (ICAM-1, CD54) and the transferrin receptor (CD71) in the complement-independent uptake of L. pneumophila. To exclude any influence of culture conditions onto phagocytosis rates, we compared a fresh clinical isolate with an agaradapted isolate of L. pneumophila. In addition, we used three different host cell types (MM6, HeLa and Jurkat cells) expressing different rates of complement receptors. We could show that both strains of L. pneumophila were phagocytized by the three host cell lines to the same extent, but intracellular multiplication was only found in MM6 and, although to a much lesser degree, in Jurkat cells. Preincubation of MM6 cells with monoclonal antibodies directed against the above cited phagocytosis-related receptors did not result in inhibition of L. pneumophila uptake. We therefore conclude that typical phagocytosis-related cell surface receptors are not involved in the complementindependent phagocytosis of L. pneumophila. ß