Inhibition of histamine release from rat peritoneal mast cells by a factor from human serum--identification as transferrin.

Recently, we described the presence of a blocking factor (BF) in rat serum which inhibited the histamine release from rat mast cells in vivo and in vitro. The blocking activity was demonstrated in human serum as well. Purification of the human-BF was carried out in a similar way as previously described for the rodent molecule. Both protein fractions produced a marked suppression of histamine release from rat mast cells and human basophils in a dose-dependent fashion. Qualitative analysis of the purified preparations demonstrated a major component with a molecular weight of 70,000 daltons. In human serum the blocking factor was identified as transferrin by serological and biochemical methods. It is suggested that this molecule may play an important role in regulating histamine release during allergic and inflammatory reactions.