The present invention concerns chimeric or humanized antibodies or antigen-binding fragments thereof that comprise specific CDR sequences, disclosed herein. Preferably, the antibodies or fragments comprise specific heavy and light chain variable region sequences disclosed herein. More preferably, the antibodies or fragments also comprise specific constant region sequences, such as those associated with the nG1m1,2 or Km3 allotypes. The antibodies or fragments may bind to a human histone protein, such as H2B, H3 or H4. The antibodies or fragments are of use to treat a variety of diseases that may be associated with histones, such as autoimmune disease (e.g., SLE), atherosclerosis, arthritis, rheumatoid arthritis, edema, sepsis, septic shock, hyperinflammatory disorder, infectious disease, inflammatory disease, immune dysregulatory disorder, GVHD, transplant rejection, atherosclerosis, asthma, a coagulopathy, myocardial ischemia, thrombosis, nephritis, inflammatory liver injury, acute pancreatitis, ischemia-reperfusion injury, stroke, cardiovascular disease, and burn.