Interesting article just published in "The Proceedings of the National
Academy of Sciences", and summarised here.  David

Research Uncovers Why AIDS Can't Be Transmitted
Through Saliva
http://www.pslgroup.com/dg/ec8d6.htm

Researchers have identified an ordinary protein
present in tears and saliva and breast milk that is the long-sought
mystery substance in the urine of pregnant women
which serves as a powerful anti-HIV agent.