The objective of this section is to promote a dialogue between practitioners and investigators in the field of contact dermatitis. Because T cells only recognize peptide antigens, one of the most intriguing aspects of allergic contact dermatitis is the fact that the allergens involved are chemicals (haptens) and not proteins. The following report by Hans Ulrich Weltzien reviews the most contemporary studies concerning molecular recognition of haptens by T cells. Readers are encouraged to submit questions for future articles and to provide feedback.
This report attempts to summarize recent developments in the understanding of T-cell-based immune reactions to haptens, ie, to chemically altered selfproteins. Surprising to some of us, haptens seem to be recognized by exactly the same molecular mechanisms as are “normal” protein antigens, ie, in the form of hapten-modified short peptides tightly associated with major histocompatibility complex (MHC)-encoded MHC antigens. The speciality of haptens, reflected in often unusually strong antigenicity and profound allergenic properties, may relate to the fact that many T cells react to them in an MHC-restricted but carrier-independent fashion. Chemical cell modification thus results in a particularly repetitive array of cross-reactive, immunodominant determinants. The use of synthetic, hapten-modified, MHC-binding peptides now allows detailed molecular analyses of hapten-directed T cell reactivities in vitro as well as in vivo, including hapten-induced contact sensitivity reactions.
