How can an infection trigger a cross-reaction against healthy cells?

A cross-reaction occurs when an infectious agent possesses antigens that are structurally similar to those found on the body's own healthy tissues. Because these foreign and self-antigens share common epitopes—the specific molecular patterns recognized by the immune system—the antibodies or lymphocytes generated to fight the infection may also bind to and damage the host's healthy cells.123

This process is a significant mechanism in certain autoimmune disorders. For example, in rheumatic fever, the immune system produces antibodies against streptococcal bacteria that inadvertently cross-react with heart muscle membranes, leading to tissue damage. Similarly, in Chagas disease, antibodies directed against trypanosomes can interact with specialized nerve cells in the bowel, disrupting normal function.14

While the immune system typically employs mechanisms to eliminate or suppress self-reactive cells, this cross-reactivity demonstrates how an external infection can bypass these safeguards and trigger an unintended attack on the body's own components.156