Salivary protein which prevents transmission of HIV via saliva is

The low rate of recovery of infectious HIV from saliva could reflect not only relatively low virus content but also direct antiviral properties of saliva fluid, such as the secretory leukocyte protease Inhibitor. It blocks cell receptors needed for entry of virus. A salivary protein called secretory leucocyte protease inhibitor (SLPI), blocks the AIDS virus from infecting critical immune system cells, which are targeted by the virus.