Outer membrane protein A (OmpA), peptidoglycan-associated lipoprotein (PAL), and murein lipoprotein (MLP) are released in experimental Gram-negative sepsis

We previously showed that Escherichia coli bacteria incubated in normal hum an serum release complexes that contain three conserved Gram-negative bacte rial outer membrane proteins (OMPs) and LPS. We have identified the OMPs as outer membrane protein A (OmpA), peptidoglycan-associated lipoprotein (PAL ), and murein lipoprotein (MLP). These OMPs are conserved among enteric Gra mnegative bacteria and are bound by IgG in antisera raised to heat-killed r ough bacteria such as E. coli J5 (J5 IgG). The present experiments were per formed to further analyze the release of these OMPs in a rat wound infectio n model of sepsis. Plasma was collected from thermally injured rats with E. coli O18 sepsis and filtered. LPS was affinity-purified from plasma filtra tes using monoclonal antibody specific for the O-polysaccharide side chain of E. coli O18 LPS. Plasma filtrates were also incubated with J5 IgG conjug ated to magnetic beads. Affinity-purified samples were analyzed for the OMP s by immunoblotting. OmpA, PAL, and MLP were released into septic rat blood in complexes with LPS. PAL was consistently present in samples affinity-pu rified using J5 IgG. The results indicate that OmpA, PAL, and MLP are relea sed and circulate in experimental Gram-negative sepsis and suggest that a p roportion of released OMPs are tightly associated with LPS.