Which one of the following statements regarding immunisation and the immune system is false?

The statement that erythrocytes are released during the immune response is not accurate. During an immune response, the body mainly mobilizes leukocytes, or white blood cells, to fight off pathogens. Erythrocytes, or red blood cells, primarily function in oxygen transport and do not play a direct role in the immune response. Instead, they are involved in carrying oxygen from the lungs to the body's tissues and returning carbon dioxide from the tissues back to the lungs.

The other statements provide accurate information: immunization is designed to generate antibodies that can protect individuals from serious diseases; immunoglobulins, which are antibodies, can indeed be found in saliva and contribute to the mucosal immune system; and natural immunity can occur when a person’s body has previously been exposed to a disease or pathogen, thus allowing it to develop antibodies and immune memory without vaccination. Each of these reflects a true aspect of immunisation and the immune system functions.