Pneumolysin causes cyotoxicity and ciliary stasis in human respiratory epithelial cells

Background: Pneumolysin is the cholesterol dependent pore forming toxin that is released from Streptococcus pneumoniae during respiratory infection. The release of pneumolysin is thought to be a sudden event following activation of the bacterial autolysin enzyme. Here we tested the dose response relationship of acute exposure of pneumolysin on human respiratory epithelial cells grown at an air-liquid interface. Aims: To determine the concentration of pneumolysin required to adversely affect human respiratory ciliary function. Methods: Normal human respiratory epithelial cells were grown to a confluent layer and re-growth of cilia from the basal epithelial cells was stimulated by use of an air-liquid interface culture. Light microscopy and high speed video recordings at 1000x magnification were used to determine cilia function and morphological cytotoxicity. Results: Pneumolysin displayed a dose dependent inhibition of ciliary beat frequency with an IC 50 of 43.3± 6.9 HU . The common cytotoxic events that were quantified included ciliary dyskinesia, immotility and cytoplasmic extrusion. Conclusion: Pneumolysin caused dose dependent, rapid ciliary inhibition and cytotoxicity, indicating an important role of this toxin in pneumococcal infection. The comparative toxicity with un-ciliated basal cells will be presented.