Reported that GAG family members, including R428 dextran sulfates with average heparin, heparan sulfate and CSA at concentrations from 100 to 1000 mg/ ml could inhibit complement. Dextran sulfate with an average MW of 500,000 had the strongest inhibition. The inhibition was due to GAG enhancement of the second-order rate constant of the inactivation of C1s by C1inh. OSCS was initially identified as a contaminant in certain lots of heparin that were associated with severe adverse events. Heparin is a polydisperse mixture of linear acidic polysaccharides, which is isolated by extraction from animal tissues, most commonly porcine intestines, and is a member of the glycosaminoglycan family. OSCS had been previously prepared from chondroitin sulfate, another member of the GAG family having similar backbone structure with heparin, by chemical sulfonation, and was shown to have anticoagulant activity. Patients that received the OSCS contaminated heparin developed hypotension, shortness of breath and GI symptoms compatible with contact system activation. In vitro studies showed OSCS activated contact system Factor XII and induced kinin-kallikrein activation. OSCS also induced the generation of the anaphylactoid toxins C3a and C5a in a manner that bypassed the C3 and C5 
convertases but was also dependent on FXII. The impact of GAGs on complement and the observed effect of OSCS on complement components C3 and C5 suggested further evaluation of OSCS and complement. Investigation of the OSCS interactions with complement components using surface plasmon resonance by Linhardt��s group suggested that OSCS can bind to the complement components with moderate to high affinity comparable to that of heparin. Therefore a difference in the impact of OSCS-contaminated versus uncontaminated heparin is not explained by differences in binding to complement components. The impact of OSCS on the functional complement activity was not performed yet, which became the aim of our study. In earlier work, the complement function has been tested in vitro using a variety of models such as the standard 50% hemolytic complement assay, the enzyme immunoassay and the liposome immunoassay. In this study, we used an established model of Foretinib natural antibody mediated bacterial lysis through the complement classical pathway. The murine monoclonal polyreactive antibody 2E4 can bind with bacteria E. coli BL21, fix complement, lyse bacteria and generate anaphylatoxin C5a. This is a relevant model to study the impact of OSCS, OSCS-contaminated heparin lots, un-contaminated heparin lots and other GAGs on the complement classical pathway. Using this biologically relevant model, antibody mediated complement-dependant bacterial lysis, we demonstrated that OSCS can inhibit the complement classical pathway as indicated by lower level of C3 fixation on bacteria as well as decreased bacterial lysis. Initially, we hypothesized that C3 consumption might explain the decreased fixation of C3b on the antibodytreated bacteria. This hypothesis was consistent with the FXIIdependent OSCS induction of C3a as well as C5a. We ruled this out as the depletion of FXII from plasma did not decrease complement inhibition by OSCS. In addition, C3 is an abundant protein in normal plasma with reference values of 0.67�C1.29 g/L, and thus unlikely to be consumed to levels that would impact C3 fixation.