Serum histamine and the elicitation of murine contact sensitivity

We report that challenge of previously contact-sensitized mice results in a significant increase in the concentration of serum histamine. In an attempt to determine whether this phenomenon might form the basis of an alternative method for the evaluation of elicitation reactions in experimental contact sensitivity, we have compared challenge-induced increases in ear thickness with elevations in serum histamine. Challenge of sensitized mice revealed that both ear thickness changes and increases in the serum level of histamine were dependent upon the concentration of oxazolone used for sensitization. The kinetics of changes in serum histamine concentration were found to be biphasic, with a small increase measurable 2 h following challenge and the maximal response at 24 or 48 h. In contrast, increases in ear thickness were monophasic, although maximum responses were also observed at 24 h. It is concluded that, although they do not exactly parallel increases in ear thickness, changes in histamine concentration may provide a useful serological correlate of the challenge reaction in contact sensitivity.