To the Editor.—
The report of O'Dell et al in the Archives (1980;116:559-561) showed that a higher concentration of 2,4-dinitrochlorobenzene (DNCB) was required to elicit a detectable response in sun-damaged skin than in undamaged skin of previously sensitized persons. The concentration of DNCB required to produce reactivity was no different in the same skin sites of control subjects who did not have sun-damaged skin. These data suggested to the authors "the existence of a local defect in cell-mediated immunity in skin altered by long-term sun exposure."As postulated by the authors, a local defect in cellmediated immunity could account for their findings, but I believe there are alternate explanations. For example, the cell-mediated response may be normal, and a decreased reactivity could reflect an alteration in the carrier protein(s) to which the DNCB is bound.To elaborate, the determinants of specificity are smaller and less complex in the antibody-mediated