Studies on the retest reaction in contact sensitivity to DNCB.

DNCB-sensitized guinea pigs demonstrated an accelerated reactivity on retest of DNCB at the site of prior contact reaction, though presenting normal contact sensitivity at the virgin site. The retest reaction reached maximal at 9 h and waned at 24 h after antigenic challenge. Massive accumulation of eosinophils in either the epidermis or dermis was its distinguishing histologic feature. The reaction was induced at the site of delayed skin reaction to DNP-GPE in the animals sensitized with DNCB or DNP-GPE. A retest reaction in delayed sensitivity to DNP-GPE was also elicited at the site of contact reaction to DNCB in the animals. The significance of these findings is discussed.