Parotid salivary basic proline-rich proteins inhibit HIV-I infectivity

OBJECTIVE: The objective of this study was to investigate the molecular nature, spectrum of activity and mechanism(s) of action of those human parotid basic pro-line-rich proteins that exhibit anti-HIV-1 activity. DESIGN: Fractions containing the basic proline-rich proteins were obtained from human parotid saliva of presumed HIV-1 non-infected human subjects and characterized with respect to their purity, apparent molecular size and their ability to inhibit the infectivity of Tropic and M-tropic strains of HIV-1. SUBJECTS, MATERIALS AND METHODS: Stimulated parotid saliva samples were collected from human subjects who denied having any risk factors for HIV-1 infection and whose parotid salivas inhibited HIV-1 infectivity. Such samples were subjected to affinity, molecular sieve and ion exchange chromatography to isolate individual salivary components. Those fractions demonstrating anti-HIV-1 activity were analyzed by SDS-PAGE in order to assess their purity and determine their apparent molecular weights, HIV-1 inhibitory activity was determined using HIV-1 strains LAI and BaL in a Hela cell-derived multinuclear activation of a galactosidase indicator (MAGI) assay. Amino acid analyses were performed on some fractions. RESULTS: Recombinant gp120-CH-Sepharose chromatography of one subject's parotid saliva revealed specific binding of human parotid basic proline-rich proteins, most prominently one with an apparent molecular weight of 37 kDa, Molecular sieve and cation exchange chromatography yielded a fraction greatly enriched in this protein which amino acid analysis confirmed was proline-rich, A similar fraction from two other subjects also contained basic proline-rich proteins of similar molecular size, These fractions inhibited both T-tropic and M-tropic strains of HIV-1 when assayed in the MAGI system, Since SLPI activity is not observable in the MAGI assay, this inhibition was not due to SLPI, The presence of thrombospondin-I (TSP-I) in the active fractions was precluded on the basis of SDS-PAGE examination. CONCLUSIONS: Specific basic proline-rich proteins in human parotid saliva possess significant anti-HIV-1 activity independent of that attributable to SLPI or TSP-I. Since the inhibition is detectable with the MAGI assay, its mechanism of action involves virus-host cell interaction prior to the introduction of the tot gene product into the host cell and may be through the binding of the basic proline-rich proteins to the HIV-1 gp 120 coat of the virus.