The correct answer is D. Interleukin-31. 

Recognize the pruritic plaques, which are now lichenified, as a common
presentation of atopic dermatitis. Pruritogenic interleukin-31 is, of the options
shown, most responsible for the pruritus in this condition.

Defensins—a type of antimicrobial peptides—are decreased in atopic dermatitis, thus making patients at an increased risk for infection. Histamine, while a mediator of itch, is less implicated compared with other neuropeptides and cytokines in atopic dermatitis. Interleukin-2 and transforming growth factor-beta are not implicated in itch compared with interleukin-31.

References:

Kwatra SG, Misery L, Clibborn C, Steinhoff M. Molecular and cellular mechanisms of itch and pain in atopic dermatitis and implications for novel therapeutics. Clin Transl Immunology. 2022;11(5):e1390. Published 2022 May 9.