PNEUMOCYSTIS-CARINII INDUCES INTERLEUKIN-6 PRODUCTION BY AN ALVEOLAR EPITHELIAL-CELL LINE

Background Pneumocystis carinii (PC) infection often results in severe pneumonia in immunocompromised patients. Attachment of PC organisms t o alveolar epithelial cells is a hallmark of PC pneumonia; however, fe w studies have investigated the response of alveolar epithelial cells to PC infection. Methods Interleukin 6 (IL-6) is a multifunctional cyt okine that is produced by alveolar epithelial cells in response to a v ariety of stimuli. Our investigation was undertaken to determine wheth er PC organisms induce production of IL-6 by alveolar epithelial cells and to determine the effect of IL-6 on PC attachment. Results Incubat ion of the human alveolar epithelial cell line, A549, with PC organism s resulted in a significant increase in IL-6 secreted into the cell cu lture media. Time-course studies showed that LL-ti production was dete cted as soon as 2 h after addition of PC and continued up to 48 h of e xposure. Further studies demonstrated that preincubation of A549 cells with IL-6 resulted in a concentration-dependent increase in both A549 cell production of fibronectin and PC attachment. Conclusion Thus, PC attachment to an alveolar epithelial cell Line results in epithelial cell production of IL-6, which can act to further increase PC attachme nt. This may provide an important mechanism whereby PC organisms direc tly affect the host response to PC infection.