A 48-year-old woman presents with a 2-month history of recurrent oral ulcers and flaccid bullae on the chest and axillae. Direct immunofluorescence shows intercellular IgG deposition in the epidermis. Among the autoimmune mechanisms in pemphigus vulgaris, what is the most common target antigen?

Explanation

## Most Common Target Antigen in Pemphigus Vulgaris **Key Point:** Desmoglein 3 (Dsg3) is the most common target antigen in pemphigus vulgaris, present in nearly 100% of cases. Anti-Dsg3 antibodies define the mucosal-dominant form. ### Desmoglein Classification in Pemphigus **High-Yield:** The serological profile of anti-desmoglein antibodies determines the clinical phenotype: | Antibody Profile | Clinical Type | Presentation | |---|---|---| | **Anti-Dsg3 alone** | Mucosal-dominant PV | Oral erosions only, no skin involvement | | **Anti-Dsg3 + Anti-Dsg1** | Mucocutaneous PV | Oral + widespread cutaneous involvement | | **Anti-Dsg1 alone** | Pemphigus foliaceus | Superficial, no mucosal involvement | ### Pathophysiology of Desmoglein 3 Targeting 1. **Desmogleins are transmembrane glycoproteins** — critical for cell-cell adhesion in the epidermis 2. **Dsg3 is abundant in the lower epidermis and oral mucosa** — explains why these sites are most commonly affected 3. **Anti-Dsg3 antibodies cause acantholysis** — loss of intercellular adhesion → intraepidermal blister formation 4. **Antibody titer correlates with disease severity** — higher titers predict more extensive involvement ### Clinical Pearl: Serological Correlation **Clinical Pearl:** In this patient with oral ulcers and chest/axillary bullae, anti-Dsg3 antibodies are almost certainly present. If anti-Dsg1 is also positive, the patient has mucocutaneous disease; if anti-Dsg3 alone, it is mucosal-dominant. ### Why Dsg3 is Most Common - Present in **100% of pemphigus vulgaris cases** - Dsg3 is the **primary target** in the disease pathogenesis - Anti-Dsg1 antibodies (seen in ~50% of PV cases) are secondary to anti-Dsg3 - Dsg1 alone (without Dsg3) causes the superficial form (pemphigus foliaceus), not PV **Mnemonic:** **Dsg3-FIRST** — **D**esmoglein **3** is the **F**irst and **I**nitial **R**ecognized **S**erological **T**arget in pemphigus vulgaris. ### Immunofluorescence Correlation **Key Point:** Direct immunofluorescence (as in this case) shows **intercellular IgG deposition** in a "chicken-wire" or "tombstone" pattern — this is pathognomonic for pemphigus and reflects antibody binding to desmogleins on the cell surface. [cite:Robbins 10e Ch 25; Harrison 21e Ch 325]