Skip Navigation


Author(s): Nancy Moreno, PhD, Barbara Tharp, MS, Deanne Erdmann, MS, Sonia Rahmati Clayton, PhD, and James Denk, MA.

Defending Against Microbes

We are surrounded by potential disease-causing microbes, yet most of us remain remarkably healthy. How do our bodies protect themselves against infections by microorganisms and viruses? The answer lies with the remarkable immune system, which consists of many types of proteins, cells, organs and tissues—all working together to identify and destroy foreign invaders (primarily microbes) and abnormal cells (such as tumor cells) within the body. 

A healthy immune system can distinguish between the body’s own cells (including helpful microbes inside the body) and foreign cells. When immune system cells detect foreign cells or organisms, they quickly attack. Anything that triggers this immune response is called an “antigen.” An antigen can be a microbe, a part of a microbe, or even cells from another organism (such as from another person). Parts of the immune system also can remember a disease-causing agent (or pathogen) and mount an attack if the pathogen reappears. These immunological memories are the basis of vaccination. Vaccines “teach” the immune system to recognize a specific pathogen by mimicking a natural infection by that pathogen. 


1. Ask students, If microbes are everywhere, why aren’t we sick all the time? Conduct a class discussion or make a list of students’ ideas on the board. If not mentioned by students, introduce the idea that the body’s defense system—called the immune system—helps to find and destroy microbes. 

2. Distribute a copy of the “Germ Defense” article (see PDF) to each student. Have students read the article individually and then discuss it within their groups. Students should use their markers to highlight new words or concepts they find in the article. 

3. Within their groups, have students discuss the words or concepts they highlighted. Encourage groups to search the Internet for additional, related information. Reliable websites include the National Institutes of Health ( and the Centers for Disease Control and Prevention ( 

4. Have students use what they have learned to complete the crossword puzzle, individually or in groups. 

5.  Allow time for students to add to their concept maps.

Funded by the following grant(s)

Science Education Partnership Award, NIH

Grant Number: 5R25RR018605