Q.In which of the following human diseases does the body's self-defence mechanism attack self-cells ? (A) Thalassemia (B) Phenylketonuria (C) Filariasis (D) Rheumatoid arthritis

The key idea is autoimmunity.

An autoimmune disease is a condition where the body's immune system mistakenly attacks its own healthy cells and tissues, failing to distinguish between self and non-self.

1. Thalassemia and Phenylketonuria are genetic disorders, not autoimmune conditions.
2. Filariasis is a parasitic infection. …

Our immune system is a sophisticated defence mechanism designed to protect us from foreign invaders like bacteria, viruses, and parasites. It achieves this by distinguishing between "self" cells (our own body cells) and "non-self" cells (foreign entities). This ability to differentiate is crucial for maintaining health. However, sometimes this mechanism goes awry, leading to conditions where the immune system loses its tolerance for self-cells and begins to attack them. These conditions are known as autoimmune diseases.

Let's examine each option to determine which one fits this description.

1. Thalassemia: This is a genetic blood disorder. It's caused by mutations in the DNA that affect the production of hemoglobin, the protein in red blood cells that carries oxygen. The body's immune system does not attack its own cells in thalassemia; rather, there's a defect in the red blood cell production itself.

2. Phenylketonuria (PKU): This is also a genetic metabolic disorder. Individuals with PKU lack a specific enzyme (phenylalanine hydroxylase) needed to break down the amino acid phenylalanine. This leads to a buildup of phenylalanine in the body, which can cause neurological problems. Like thalassemia, PKU is not an autoimmune disease; it's a problem with metabolism due to a genetic defect.

3. Filariasis: This is an infectious disease caused by parasitic worms called filariae. These worms are transmitted to humans through mosquito bites. The immune system responds to the presence of these parasites, but it is attacking a foreign invader, not the body's own cells. Therefore, it is not an autoimmune disease. …