Pneumocystis Cell Wall Beta-glucans Stimulate Alveolar Epithelial Cell Chemokine Generation Through Nuclear Factor-kappaB-dependent Mechanisms

Exuberant inflammatory responses are associated with respiratory failure during Pneumocystis pneumonia. Alveolar epithelial cells (AECs) promote Pneumocystis attachment and proliferation, but also contribute prominently to host cytokine-mediated inflammation during pneumonia. Recent investigations indicate that AECs produce macrophage inflammatory protein-2 (MIP-2) and tumor necrosis factor-alpha (TNF-alpha) following challenge with Pneumocystis carinii. Nuclear factor-kappaB (NF-kappaB) is a ubiquitous transcription factor critical for regulation of proinflammatory cytokine expression. Herein, we assess rat AEC NF-kappaB responses to challenge with a P. carinii beta-glucan cell wall component (PCBG). Prominent nuclear translocation of p65 NF-kappaB was demonstrated following PCBG challenge. NF-kappaB activation was in part mediated through Protein Kinase C (PKC) signaling pathways. PCBG challenge of AECs was also shown to induce MIP-2 and TNF-alpha mRNA production, a response that was ameliorated by NF-kappaB inhibition. MIP-2 protein expression was also dramatically increased by PCBG challenge, in a manner that was significantly attenuated by both PKC and NF-kappaB inhibition. The data further demonstrate that AEC chemokine responses were not mediated by the recently described dectin-1 receptor, but instead involved participation of cell surface lactosylceramide. These data support a significant role for AECs in host responses during Pneumocystis pneumonia, and further indicate that beta-glucan induces inflammatory cytokine production through NF-kappaB-dependent mechanisms.