A human milk factor susceptible to cathepsin D inhibitors enhances human immunodeficiency virus type 1 infectivity and allows virus entry into a mammary epithelial cell line

Human immunodeficiency virus type 1 (HIV-I) growth in lymphocyte cultures w as increased when the virus inoculum was incubated in breast milk The enhan cing effect of milk was abolished by anti-cathepsin D antibody or by pepsta tin A, a cathepsin D inhibitor. The cathepsin D-producing CD4-negative MCF7 mammary cells supported the growth of some HIV-1 isolates. An MCF7 line ch ronically producing HIV-1 IIIb was obtained. Cathepsin D may induce conform ational modification of viral gp120, allowing direct interaction with a cor eceptor. We demonstrated the presence of CXCR4 mRNA in MCF7 cells.