A milk protein lactoferrin enhances human T cell leukemia virus type I and suppresses HIV-1 infection.

Human T cell leukemia virus type I (HTLV-I) and HIV-1, causative agents of adult T cell leukemia/lymphoma and AIDS, respectively, are transmitted vertically via breast milk. Here we demonstrate that lactoferrin, a milk protein that has a variety of antimicrobial and immunomodulatory activities, facilitates replication of HTLV-I in lymphocytes derived from asymptomatic HTLV-I carriers and transmission to cord blood lymphocytes in vitro. Transient expression assays revealed that lactoferrin can transactivate HTLV-I long terminal repeat promoter. In contrast, lactoferrin inhibits HIV-1 replication, at least in part, at the level of viral fusion/entry. These results suggest that lactoferrin may have different effects on vertical transmission of the two milk-borne retroviruses.