Secretory leukocyte protease inhibitor blocks infectivity of primary monocytes and mononuclear cells with both monocytotropic and lymphocytotropic strains of human immunodeficiency virus type I.

Saliva contains factors that inhibit infection with the human immunodeficiency virus type 1 (HIV-1) in vitro. One of these factors was recently identified as secretory leukocyte protease inhibitor (SLPI), a salivary protein which blocked HIV-1 infectivity of monocytes and primary T cells at physiologic concentrations (J Clin Invest 1995; 96: 456). Here, we confirm and extend the original report by demonstrating that SLPI protects primary monocytes and peripheral blood mononuclear cells against infection with HIV-1 Ba-L, IIIB and NL4-3. Thus, SLPI may provide a natural barrier against oral transmission of HIV-1.