1.   Couples who acted less loving toward each other had decreased levels of disease-fighting antibodies and killer T-cells, which knock out invading viruses.

2.   His T-cells, an immune system cell that fights invading viruses, continued to fall.

3.   Nobody yet knows where the invading virus came from, as this is a devilishly difficult disease to track.

4.   The police force comprises white blood cells that battle invading viruses.

5.   Their immune systems collapsed and the invading viruses reproduced in a frenzy that spawned high levels of virus.

6.   They engulf and destroy invading viruses and bacteria.

7.   Unlike a flu shot, AIDS vaccines do not actually prevent infection by the invading virus.

8.   Unlike a flu shot, AIDS vaccines do not actually prevent infection by stimulating antibody molecules that neutralize the invading virus.

9.   Naive lymphocytes are so called when they have not come into contact with an invading virus.