Updates on the Pathogenesis of Canine Atopic Dermatitis and Feline Atopic Skin Syndrome: Part 2, the Skin Barrier, the Microbiome, and Immune System Dysfunction.

Alterations in the lipid layer and intercellular corneocyte connections can lead to increased allergen penetration through the skin surface. A normal cutaneous microbiome keeps the opportunistic pathogen Staphylococcus pseudintermedius levels low, but allergic inflammation leads to decreased diversity and increase in S pseudintermedius. Keratinocytes sound the initial allergen alarm via cytokine signaling and promote T-helper 2 (Th-2) inflammation. Th-2 cytokine products IL-4, IL-13, and IL-31 are increased in the acute allergic inflammatory response. Altered response in T-helper 1, T-helper 17, and T-regulatory cells play a role in both acute and chronic allergic inflammation.