Impaired Delayed Hypersensitivity

To the Editor:— I was very much interested in the report of Waldorf et al (203:831, 1968) concerning the impairment in skin reactivity of older individuals after the induction of delayed skin test reactions by the application of patch tests of 2, 4-dinitrochlorobenzene (DNCB). While these studies involved delayed skin test reactions, I wondered whether any of these individuals also had been tested with allergens producing immediate-type skin test reactions and if so, whether such reactions also were reduced in intensity. I am interested because in July 1955 my associates and I1reported the results of studies designed to show the influence of age upon skin reactivity as applied to direct skin test reactions. To determine this, we did intradermal skin tests upon nonallergic individuals in all the age decades from infancy on, with histamine solution diluted 1:1,000, 1:10,000, 1:100,000, and 1:million, using 100 individuals for each decade