Q.Explain the mechanism by which an allergic reaction occurs in the body, and describe what goes wrong in an autoimmune disorder, using rheumatoid arthritis as an example.

Mechanism of an allergic reaction: An allergy begins when a susceptible person is first exposed to an allergen — a substance, such as dust, pollen, or animal dander, that is harmless to most people. In this person, the immune system produces IgE antibodies specific to that allergen, and these IgE molecules attach to the surface of mast cells found throughout body tissues, particularly near the skin, airways, and gut. On a later exposure to the same allergen, the allergen binds to the IgE already sitting on the mast cells, triggering those cells to rapidly release chemical mediators — most importantly histamine — into the surrounding tissue. Histamine is responsible for the familiar symptoms of an allergic reaction: sneezing, watery and itchy eyes, skin rashes, and, in the airways, the narrowing that causes wheezing and breathlessness seen in allergic asthma. Management relies on avoiding the known allergen and using antihistamine medicines to block histamine's effects.

Autoimmune disorders, using rheumatoid arthritis as an example: An autoimmune disorder occurs when the immune system's normal ability to distinguish the body's own tissue ("self") from foreign material ("non-self") breaks down. Instead of directing its attack at a genuinely foreign antigen, the immune system mounts a sustained attack against some of the body's own healthy tissue. In rheumatoid arthritis, this misdirected attack specifically targets the tissue lining the joints, producing chronic inflammation, pain, and swelling that, if left unmanaged, leads to progressive joint damage over time. …

End a comparative long answer like this with an explicit 'key contrast' sentence — examiners reward answers that not only describe both mechanisms co …

Do not describe an autoimmune disorder as simply 'a stronger allergy' — the two are mechanistically distinct: allergy is an overreaction to a real foreign substance (mediated by IgE and mast cells), while an autoimmune diso …