**Question:** The following is an important feature of psoriasis: September 2009

A. Increased epidermal cell proliferation
B. Altered keratinocyte differentiation
C. Reduced epidermal cell apoptosis
D. Enhanced immune response

**Core Concept:** Psoriasis is a chronic inflammatory skin disorder characterized by excessive epidermal cell proliferation, leading to the formation of scaly plaques. The underlying pathophysiology involves alterations in keratinocyte differentiation, apoptosis, and immune response.

**Why the Correct Answer is Right:** The correct answer, D. Enhanced immune response, is crucial in understanding the pathogenesis of psoriasis. The disease is considered an autoimmune disorder, where the body's immune system attacks the skin cells, leading to overproduction and accumulation of keratinocytes in the epidermis.

**Why Each Wrong Option is Incorrect:**

A. Increased epidermal cell proliferation is partially correct but does not encompass the full picture of psoriasis. The focus on cell proliferation alone does not explain the abnormal keratinocyte differentiation and reduced apoptosis observed in the disease.

B. Altered keratinocyte differentiation is partially correct, but it does not address the primary cause of the excessive epidermal cell proliferation, which is the enhanced immune response.

C. Reduced epidermal cell apoptosis is partially correct but does not explain the primary cause of the excessive epidermal cell proliferation observed in psoriasis. The focus on apoptosis alone does not account for the abnormal keratinocyte differentiation and immune response involved in the disease.

**Clinical Pearl:** Understanding the role of immune system dysregulation and keratinocyte proliferation in psoriasis is crucial for effective diagnosis and treatment planning. Treatment strategies for psoriasis involve modulating the immune response and promoting healthy keratinocyte differentiation, such as with biologic agents targeting cytokines involved in the disease process.