Any sort of "foreign" substance can, and most often will, elicit an immune response under certain curcumstances--provided the immune system is healthy. This would include bacteria, viruses and fungi.
Related: An unhealthy, or compromised immune system can act in all sorts of undesirable ways, ranging from low response to threat or injury to actually creating antibodies to attack its own system or other organs and tissue.
The protein that elicits an immune reaction in blood cells is called an antigen. Antigens are typically foreign substances that trigger an immune response when they are detected by the immune system.
Antigen is the medical term meaning foreign substance.
Immune System
An antigen is a substance that produces an immune response in the body, typically by binding to specific antibodies or activating immune cells. This immune response is essential for recognizing and eliminating foreign substances such as pathogens.
Antigen
An antigen is a substance that triggers an immune response in the body, by stimulating the production of antibodies. This response helps the body to recognize and destroy harmful pathogens such as bacteria, viruses, or foreign substances.
Antigen
a toxin or other foreign substance that induces an immune response in the body, especially the production of antibodies.
A response of the body to an invasion of foreign substances is inflammation. The immune system will also produce more white blood cells and send them to the site of the infection.
Antigenan·ti·gen/ˈantijən/Noun:A toxin or other foreign substance that induces an immune response in the body, esp. the production of antibodies.
Lymphocytes
An antibody is a substance formed by the body in response to a perceived foreign substance. Antibodies are produced by the immune system to help identify and neutralize potentially harmful invaders, such as bacteria and viruses.