If foreign substances pass the body's first line of defense and into the bloodstream, what happens?

They are attacked by lymphocytes.

Explanation:

Our body has a strong defense system that protects us from various diseases.

If foreign substances pass through the body's first line of defense and enter the bloodstream, they may not be able to attack our body, because they will be attacked by lymphocytes, which are the cells known as white blood cells.

Lymphocytes are produced in high concentration when our body is being attacked by an infection, or foreign particle. When this occurs, these cells attack the infection or the substance in a violent way, forcing it to leave our body.