Random Dermatology MCQ - Leukocytes' Role in Skin

A 45-year-old woman presents with a well-demarcated, erythematous, and scaly plaque on her elbow. A biopsy reveals epidermal hyperplasia (acanthosis) and a dense dermal infiltrate composed predominantly of cells with a multilobed nucleus and abundant granules in their cytoplasm. Which of the following cell types is the most abundant in this infiltrate and is primarily responsible for the clinical signs of acute inflammation in this psoriatic plaque?

A) Neutrophils
B) Lymphocytes
C) Eosinophils
D) Mast cells
E) Macrophages

Correct Answer: A) Neutrophils

Explanation

This question tests the understanding of key leukocytes and their specific roles in classic inflammatory skin diseases, using psoriasis as the model.

Leukocyte Roles in the Skin:

1. Neutrophils (Polymorphonuclear Leukocytes)

   • Identification: Characteristic multilobed (segmented) nucleus and cytoplasmic granules containing myeloperoxidase, defensins, and proteases.

   • Primary Role: First responders in acute inflammation and pyogenic infections. They phagocytose pathogens and release inflammatory mediators.

   • Role in Psoriasis: A hallmark of active psoriasis is the presence of Munro microabscesses (collections of neutrophils in the stratum corneum) and spongiform pustules of Kogoj (neutrophils in the epidermis). They contribute to the erythema, scale, and pustulation.

2. Lymphocytes

   • Role: Key players in adaptive immunity.

   • T-cells (CD4+ and CD8+): Central to chronic inflammatory and autoimmune diseases like psoriasis, atopic dermatitis, and lichen planus. They orchestrate the immune response.

   • B-cells: Produce antibodies. Less abundant in most inflammatory dermatoses but crucial in autoimmune blistering diseases (e.g., pemphigus).

3. Eosinophils

   • Identification: Bilobed nucleus and granules containing major basic protein.

   • Role: Primarily involved in parasitic infections and allergic reactions (e.g., urticaria, drug eruptions, eosinophilic cellulitis). Characteristic in bullous pemphigoid.

4. Mast Cells

   • Role: Residents in normal dermis. Key in IgE-mediated (Type I) hypersensitivity (e.g., urticaria, anaphylaxis). They release histamine, leukotrienes, and other mediators causing wheal and flare.

5. Macrophages

   • Role: Phagocytose debris and pathogens. They are the dominant cell in granulomatous diseases (e.g., sarcoidosis, tuberculosis) and appear later in the inflammatory process.

Analysis of This Case:

• The diagnosis is psoriasis vulgaris (well-demarcated, scaly plaque on the elbow).

• The histologic description of a cell with a multilobed nucleus and abundant granules is pathognomonic for a neutrophil.

• While psoriasis is a T-cell-mediated disease, the acute clinical signs of redness and scale are heavily driven by the recruitment and activity of neutrophils into the epidermis.

Note: In psoriasis, the sequence of events involves activated T-cells releasing cytokines (e.g., IL-17, TNF-α) that stimulate keratinocytes to produce chemokines (e.g., IL-8), which in turn recruit the neutrophils that create the characteristic microscopic and clinical findings. Therefore, while lymphocytes initiate the process, neutrophils are the dominant effector cell in the acute inflammatory infiltrate of a psoriatic plaque.