Immediate hypersensitivity to tuberculin. In vivo and in vitro studies.

Immediate responses of hypersensitivity to skin testing with purified derivative of tuberculin (PPD) were observed in 2.3 percent of 3,248 patients seen in an allergy clinic, and the relationship to delayed responses was questioned. Immediate cutaneous reactions to testing with PPD appeared in all age groups and occurred in nonatopic patients but were more common in atopic patients (p less than 0.005). Delayed cutaneous reactions to testing with PPD occurred in only three out of 76 patients with immediate reactivity. Antihistaminic suppression of immediate reactivity was not followed by evidence of delayed cutaneous reactivity. In vitro tests of lymphocytic stimulation revealed indices of stimulation with PPD to be similar both in patients with immediate and delayed cutaneous reactivity. Failure to manifest delayed cutaneous reactivity following immediate cutaneous reactions alone may be explained by antigen-antibody binding and phagocytosis, by suppressor T-lymphocytes, or by impaired release or lack of response to T-lymphocytic mediators. Adverse reactions to administration of BCG vaccine in patients with immediate cutaneous reactivity might be anticipated.