Eosinophil inhibition mitigates antibacterial effects 3679

Abstract Description Pneumonia caused by Streptococcus species can be fatal, particularly in patients recovering from influenza. Innate immune cells have antibacterial properties that counter pneumococci. Previously, we discovered eosinophils (EOS) neutralize bacteria; we aimed to determine the receptors important for this function. Inhibitors used singly or combined are TLR-4, PAFr, and CytoD. EOS were treated with IL-5, GM-CSF and inhibitors. EOS: bacteria (1:5) were seeded in a 96-well plate, incubated at varying timepoints. 100 µL mixture was retrieved for cytospins, slides were differentially stained, and cells with bacteria were counted. Additionally, inhibitor-treated EOS +/- bacteria were used in a growth curve. Our data show EOS interacted with bacteria; low optical density suggests S. pneumoniae inhibition. EOS treated with TLR-4 and PAFr alone or combined had a higher bacterial growth than untreated EOS but a comparable effect on bacteria as EOS challenged with bacteria. As expected, CytoD alone or in combination showed reduced cellular activity with or without bacteria. Slides showed EOS uptake of bacteria but at lower levels compared to inhibitor-treated EOS. Blocking EOS receptors impaired their ability to inactivate S. pneumoniae. EOS mode of pneumococcal neutralization is likely multifaceted and dependent on direct and indirect functions. Future study is aimed at delineating whether counter-interaction between surface receptors play a role in EOS antibacterial function. Funding Sources Supported by AAI High School Teachers Summer Research Program in Immunology; Plough Foundation. Topic Categories Microbial, Parasitic, and Fungal Immunology (MPF)