What causes the immune system to wrongly target self cells?

The immune system is designed to distinguish between self and non-self cells, typically allowing it to effectively respond to pathogens while leaving the body's own cells unharmed. However, in cases of autoimmune diseases, this discrimination fails. Autoimmune diseases occur when the immune system mistakenly targets and attacks the body's own cells, tissues, or organs as though they were foreign invaders.

This misidentification can happen for a variety of reasons, including genetic predisposition, environmental triggers, or the breakdown of immune tolerance, leading to specific autoimmune conditions such as rheumatoid arthritis, lupus, or type 1 diabetes. Each of these conditions is characterized by an immune response that mistakenly causes damage to self tissues, highlighting the critical role that the immune system plays in maintaining self-tolerance.

In contrast, the other choices—cross-reactivity, allergies, and infections—represent different facets of immune system activity but do not encapsulate the primary mechanism of the immune system's failure to recognize self cells as seen in autoimmune diseases. Thus, autoimmune diseases specifically highlight the phenomenon where the immune system's error leads to harmful effects on self cells.