Abstract: The present invention relates to a monoclonal antibody 3D9 specifically binding a C-terminal fragment of cleaved histone H3 in NETs that can be used to specifically detect NETs distinguishing them from chromatin of different origin. The invention also provides a method for in vitro detection of neutrophil extracellular traps in isolated biological samples as well as a method for assessing a disease condition associated with NET formation. The present invention also relates to an isolated fragment of human histone H3 cleaved at site L48R49, and to the use of cleavage site L48R49 for specific detection of human neutrophil extracellular traps. The present invention also relates to recombinant nucleic acid sequences encoding said polypeptides, and host cells comprising the same.