ABSTRACT
This chapter provides a generalized overview of the pathophysiology of atopic dermatitis (AD), looking at barrier defects, immune mechanisms, and the involvement of various cell types. Investigators have drawn a distinction between so-called ‘extrinsic atopic dermatitis’ and ‘atopiform dermatitis,’ or so-called ‘intrinsic atopic dermatitis,’ based on the presence or absence of these indicators of atopy. Abundant evidence suggests an important role for T lymphocytes in the pathogenesis of AD. Activated lymphocytes, predominantly CD4 helper cells, occur in lesional and uninvolved skin of AD patients and allergen-specific T lymphocytes can be cloned from AD lesional skin. Under normal circumstances, keratinocytes produce Antimicrobial peptides that inhibit the growth of pathogenic bacteria, fungi, and viruses on the skin surface. Studies suggest an increased baseline histamine concentration in 20–30% of AD patients, especially those with severe disease and increased plasma levels in children after positive food challenges.
