Researchers found that a small protein piece from hemoglobin, called HbB115-146, kills bacteria especially well in the acidic environment of the vagina and works even when salt is present. It also boosts the power of other natural antimicrobial proteins like LL‑37, HNP‑1, and lysozyme, especially at low pH.

Our recent studies proved that menstrual discharge is exceptionally rich in bactericidal hemoglobin peptides (hemocidins). Of special interest is the behavior of hemocidins in low pH of the vagina, in different ionic strengths, and in the presence of other specialized antibacterial molecules acting in this organ. We studied the activity of a model representative of menstrual hemocidin: the peptide from human beta-globin, spanning residues 115-146 (HbB115-146). The bactericidal action of this peptide in different physicochemical conditions, as well as the evaluation of the synergistic effect of the peptide with mixtures of neutrophil alpha-defensin HNP-1, epithelial beta-defensin HBD-1, cathelicidin LL-37 and lysozyme were studied using the bacterial membrane permeability test. The HbB115-146 is a salt-resistant antibiotic molecule strongly potentiating its activity in acidic conditions (pH 4.4-5.0), characteristic for the vagina. Hemocidin HbB115-146 is also an effective factor stimulating the activity of other antibacterial polypeptides present in the female urogenital tract. The observed synergistic effect is preserved or enhanced at lower pH and, with the exception of HBD-1, is observed also at physiological salt concentrations. The results of this study clearly demonstrate that hemocidins are important polypeptide factors involved in maintaining vaginal immunity during normal menstrual bleedings.