Proteomic and bioinformatic characterization of proteins secreted conventionally and unconventionally from human primary macrophages upon LPS transfection

The non-canonical caspase-4/5 inflammasome has been only very recently characterized. It is expressed by macrophages, the principal effector cells of the innate immunity system, and is activated by gram-negative bacteria, ER stress, and UV radiation. Activation of this inflammasome results in pyroptosis, inflammatory cell death, and secretion of pro-inflammatory cytokines of the interleukin-1 family. In our model we transfected human primary macrophages with Lipopolysaccharide, a cell wall component of gram-negative bacteria, to simulate bacteria entering the cell and thus activating the caspase-4/5 inflammasome. We then performed high-throughput proteomics to identify proteins secreted during the stimulation. The secretome was separated into two fractions using size-exclusion centrifugation, with a 100 kDa cut-off we enriched extracellular vesicles (EVs) and the flow through was concentrated over 10 kDa to yield the rest-secretome (RS) samples. The EV and RS samples of LPS transfected cells were then compared to untreated cells.