Which cytokine profile is most characteristic of the acute phase of atopic dermatitis?

Explanation

## Cytokine Profile in Atopic Dermatitis ### Th2-Mediated Inflammation in Acute AD **Key Point:** Atopic dermatitis is fundamentally a **Th2-skewed immune response** characterized by elevated interleukin-4 (IL-4), interleukin-5 (IL-5), and interleukin-13 (IL-13). ### Mechanism of Th2 Activation 1. **Barrier defect** → antigen/allergen penetration 2. **Dendritic cell activation** → Th2 polarization (via IL-4 from innate lymphoid cells) 3. **IL-4 production** → IgE class switching in B cells 4. **IL-5 production** → eosinophil recruitment and activation 5. **IL-13 production** → further IgE production and barrier dysfunction **High-Yield:** The Th2 cytokine signature explains: - Elevated serum IgE - Eosinophilia (peripheral and tissue-infiltrating) - Pruritus (IL-4 and IL-13 enhance sensory neuron responsiveness) - Impaired antimicrobial peptide production (increased *Staphylococcus aureus* colonization) ### Chronic Phase Shift In chronic/lichenified AD, there is a **shift toward Th1 and Th17 responses** with increased IFN-γ, IL-17, and TNF-α. However, the acute phase remains Th2-predominant. **Mnemonic:** **"Th2 = Atopic"** — Remember that atopy (allergic tendency) is driven by Th2 cytokines across all atopic diseases (AD, allergic rhinitis, asthma). ### Clinical Correlations | Feature | Mechanism | |---------|----------| | Pruritus | IL-4/IL-13 sensitize C-fibers; histamine from mast cells | | IgE elevation | IL-4 drives class switching; IL-13 sustains it | | Eosinophilia | IL-5 recruits and activates eosinophils | | *S. aureus* infection | Reduced IL-22 and antimicrobial peptides (LL-37) | | Barrier dysfunction | IL-13 downregulates filaggrin and ceramides | **Clinical Pearl:** Biologic therapies targeting IL-4 receptor (dupilumab) are highly effective in AD because they block both IL-4 and IL-13 signaling, addressing the core Th2 pathology.