A boy has shortness of breath, presents in OPD; is injected with penicillin. He has never shown any history of allergy. On examination, after 48 hours, his RBC’s are getting destroyed. He has been diagnosed with AIHA (Autoimmune hemolytic anaemia). Type of hypersensitivity is:

**Core Concept**
Autoimmune hemolytic anemia (AIHA) is a condition where the immune system produces antibodies against the patient's own red blood cells, leading to their destruction. This is an example of an immune-mediated reaction.

**Why the Correct Answer is Right**
In AIHA, the immune system mistakenly recognizes the red blood cells as foreign and produces IgG antibodies against them. These antibodies bind to the red blood cells and activate the complement system, leading to their destruction. This process is an example of a Type II hypersensitivity reaction, where antibodies are directed against cell-bound antigens. The mechanism involves the formation of immune complexes, activation of the complement system, and subsequent damage to the red blood cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might be incorrect because it is a type of hypersensitivity reaction that is not directly relevant to AIHA. Type I hypersensitivity reactions involve IgE antibodies and are typically associated with allergic responses.
**Option B:** This option is incorrect because it refers to a type of hypersensitivity reaction that involves cell-mediated immunity, which is not the primary mechanism in AIHA.
**Option C:** This option is incorrect because it refers to a type of hypersensitivity reaction that involves the formation of immune complexes in tissues, which is not the primary mechanism in AIHA.

**Clinical Pearl / High-Yield Fact**
In AIHA, the presence of warm autoantibodies (IgG) is more common than cold autoantibodies (IgM), and the condition is often associated with chronic lymphocytic leukemia (CLL) or lymphoproliferative disorders.

**Correct Answer:** C. Type II hypersensitivity.

✓ Correct Answer: B. Type II