Secretory leukocyte protease inhibitor (SLPI): Oxidation of SLPI does not explain its variable anti-HIV activity

Secretory leukocyte protease inhibitor (SLPI) has been proposed as a potent ial inhibitor of HIV-1 infection in human saliva. Although the ability of r ecombinant (r) SLPI to inhibit HIV-1 infection of macrophages and primary T -cells has been demonstrated by two independent laboratories, evidence to t he contrary has also been reported. This study re-examines the anti-HIV eff ect of rSLPI and investigates the effects of repeated freeze-thawing and ox idation on the anti-HIV activity of rSLPI. rSLPI inhibited HIV-1(BaL) infec tion of human macrophages in a highly variable manner. HPLC and electrospra y ionization mass spectrometry (ESI) analyses indicated that variability in our inhibition data could not be attributed to the degradation or oxidatio n of rSLPI. These results suggest that the variable anti-HIV effect of rSLP I may be due to differential expression of the cell-surface molecule(s) to which SLPI binds rather than to changes in the rSLPI molecule.