An in vitro method for quantitating specific antibodies for at least one redox form of High mobility group box 1 (HMGB1) contained in a biological sample obtained from a subject, in particular a human being, comprising: a) optionally, a step of treating the biological sample by an acid solution to dissociate the immune complexes found in the sample, preferably treating said biological sample with a Glycine solution at a low pH, more preferably treating said biological sample with Glycine 1.5M at a low pH, wherein the quantitated specific antibodies for at least one redox form of HMGB1 are total specific antibodies for at least one redox form of HMGB1; b) contacting said biological sample with at least one redox form of HMGB1 or HMGB1 derivatives as long as these derivatives bind to specific antibodies for at least one redox form of HMGB1; and c) quantitating the specific antibodies for at least one redox form of HMGB1; wherein said biological sample is diluted from 1/800 to 1/2000, preferably at 1/1000; wherein the redox form of HMGB1 is selected from the group of fully reduced HMGB1, disulfide-HMGB1 and oxidized-HMGB1; wherein when the redox form of HMGB1 is fully reduced HMGB1, the method comprises a step of treating fully reduced HMGB1 to stabilize the reduced state of HMGB1, said treatment encompassing adding a reducing agent such as dithiothreitol, β-mercaptoethanol, TCEP (tris(2-carboxyl)phosphine), in particular DTT, preferably 0.5 mM DTT, to fully reduced HMGB1; wherein when the redox form of HMGB1 is oxidized-HMGB1, the method comprises a step of treating disulfide-HMGB1 to obtain oxidized-HMGB1, said treatment encompassing adding a reactive oxygen species such as hydroxyl radical (·OH), hydrogen peroxide (H 2 O 2), superoxide radical (O 2 -), oxygen (O 2) and singlet oxygen ( 1 O 2), in particular H 2 O 2, preferably 100 mM H 2 O 2, to disulfide-HMGB1. a) optionally, a step of treating the biological sample by an acid solution to dissociate the immune complexes found in the sample, preferably treating said biological sample with a Glycine solution at a low pH, more preferably treating said biological sample with Glycine 1.5M at a low pH, wherein the quantitated specific antibodies for at least one redox form of HMGB1 are total specific antibodies for at least one redox form of HMGB1; b) contacting said biological sample with at least one redox form of HMGB1 or HMGB1 derivatives as long as these derivatives bind to specific antibodies for at least one redox form of HMGB1; and c) quantitating the specific antibodies for at least one redox form of HMGB1; wherein said biological sample is diluted from 1/800 to 1/2000, preferably at 1/1000; wherein the redox form of HMGB1 is selected from the group of fully reduced HMGB1, disulfide-HMGB1 and oxidized-HMGB1; wherein when the redox form of HMGB1 is fully reduced HMGB1, the method comprises a step of treating fully reduced HMGB1 to stabilize the reduced state of HMGB1, said treatment encompassing adding a reducing agent such as dithiothreitol, β-mercaptoethanol, TCEP (tris(2-carboxyl)phosphine), in particular DTT, preferably 0.5 mM DTT, to fully reduced HMGB1; wherein when the redox form of HMGB1 is oxidized-HMGB1, the method comprises a step of treating disulfide-HMGB1 to obtain oxidized-HMGB1, said treatment encompassing adding a reactive oxygen species such as hydroxyl radical (·OH), hydrogen peroxide (H 2 O 2), superoxide radical (O 2 -), oxygen (O 2) and singlet oxygen ( 1 O 2), in particular H 2 O 2, preferably 100 mM H 2 O 2, to disulfide-HMGB1.