In mice, giving thymosin‑alpha‑1 at a low dose (100 µg/kg) several times over two weeks boosted the number of neutrophils in the blood and made them better at killing the fungus Candida albicans. However, a single larger dose (500 µg/kg) given three days before testing actually reduced this fungus‑killing ability. The effect depends on how much and how often the peptide is taken.

In the present work we analyze the effects of thymosin alpha 1 treatment on the number and the candidacidal activity of murine polymorphonuclear leukocytes. The data we obtained showed that the treatment with thymosin alpha 1 (100 micrograms/Kg s.c.) 10, 8, 6, 4 and 2 days before the assay may result in a significant numerical augmentation of circulating polymorphonucleates in the peripheral blood, as well as of their candidacidal activity when measured in vitro in both a 4-h cytotoxicity assay and a CFU inhibition assay against Candida albicans microorganisms. On the other hand, a single dose of thymosin alpha 1 (500 micrograms/Kg s.c.) 3 days before the assay resulted in a significant decrease of the candidacidal activity of mouse polymorphonucleates. The data are discussed with regard to the immunomodulating capacity of thymosin alpha 1 and to our previously reported observations concerning the ability of the drug to modulate the resistance against systemic Candida albicans infection.