1. immune system the system in the body that works to ward off infection and disease

2. pathogen s any disease-producing agent, especially a virus, bacterium, or other microorganism

3. antibody any of numerous Y -shaped protein molecules produced by B cells as a primary immune defense

4. white blood cells colorless cells in the blood that help combat infection

5. vaccine preparation of a weakened or killed pathogen, such as a bacterium or virus, that stimulates immune cells to recognize and attack it

6. hiv (aids virus) the Human Immunodeficiency Virus (HIV) is the virus that causes AIDS (Auto Immune Deficiency Syndrome)