PneumocystisActivates Human Alveolar Macrophage NF-κB Signaling through Mannose Receptors

Abstract

Alveolar macrophages (AM) represent important effector cells in the innate immune response to the AIDSrelated pathogenPneumocystis, but the early AM host defense signaling events are poorly defined. Using AM from healthy individuals, we showed in the present study that Pneumocystis organisms stimulate AM NF-B p50 and p65 nuclear translocation in a time-dependent and multiplicity-of-infection-dependent manner as determined by electrophoretic mobility shift assay and immunofluorescence microscopy and that NF-B nuclear translocation is associated with I-B phosphorylation. Importantly, competitive inhibition of mannose receptor and targeted short interfering RNA-mediated gene suppression of mannose receptor mRNA and protein is associated with complete elimination of NF-B nuclear translocation in response to Pneumocystis.

Synergistic regulation of Pseudomonas aeruginosa‐induced cytokine production in human monocytes by mannose receptor and TLR2

“…These data are in agreement with others showing that MR is involved in NF-kB signaling induced by P. carinii [44] or cytokine, but not chemokine production induced by C. albicans [16]. However, downstream signaling pathways of MR are not well delineated and remain to be defined.…”

“…Binding of mannose to lectin prevents systemic spread of local inflammation in patients suffering from P. aeruginosa infections after burn [54]. Alternatively, down-regulation of MR expression in alveolar macrophages of HIV-infected patients correlates with increased susceptibility to opportunistic pathogens [44,55]. The successful restriction of infection is achieved by a well-orchestrated cooperative action of a network that intertwines overlapping and circulating molecules, and cell-associated receptors.…”

Decreased inflammatory response in Toll-like receptor 2 knockout mice is associated with exacerbated Pneumocystis pneumonia

“…This is consistent with previous studies showing that other receptors, such as dectin-1 and mannose receptors, also play important roles in the host response to Pneumocystis infection. [9,14] Other studies have shown that TLR2 collaborates with dectin-1 and mannose receptors to mediate inflammatory response to Pneumocystis. [15,16] A recent review by Dennehy and Brown described that dectin-1 is critical in the control of fungal infection since it can mediate its own signaling, as well as synergize with TLR to initiate responses to fungal pathogens.…”

Cdc42 and RhoB Activation Are Required for Mannose Receptor-mediated Phagocytosis by Human Alveolar Macrophages

“…Unopsonized zymosan and Pneumocystis are recognized by macrophage innate immune receptors (Ezekowitz et al, 1991;Hoffmann et al, 1999). Because sustainable cultivation of Pneumocystis is not possible, and Pneumocystis derived from human disease (P. jiriveci; Stringer et al, 2002) is rarely available, Pneumocystis organisms were obtained from chronically immunosuppressed male Lewis rats (University of Cincinnati Lab Animal Medicine Facility, Cincinnati, OH) as previously described (Zhang et al, 2004). Isolated Pneumocystis mixed-life cycle preparations yield ϳ90% trophozoite and 10% cyst forms, and viability was Ͼ85% (Chen and Cushion, 1994).…”

“…Western blot was performed as previously described (Zhang et al, 2004) using polyclonal anti-Cdc42, anti-Rac, anti-RhoB and anti-PAK, phospho-PAK, and monoclonal anti-Rho A (Santa Cruz Biotechnology). After blocking with 4% nonfat dry milk, membranes were incubated with appropriate antibodies overnight at 4°C, washed three times with TTBS, incubated with conjugated secondary antibody (1:3000) for 2 h, and washed three times with TTBS, and then the signal was detected by SuperSignal West Pico protein detection system (Pierce, Rockford, IL).…”