UC Irvine

Cutaneous delayed hypersensitivity (CDH) testing with microbial antigens in man is thought to reflect the status of cell-mediated immunity (CMI). We have evaluated diphtheria-tetanus (DT) and tetanus (T) toxoids by comparing the CDH response with in vitro parameters of CMI: lymphocyte deoxyribonucleic acid (DNA) synthesis, leukocyte inhibition factor (LIF) in 5 immunized adults, and lymphotoxin release in 2 adults. Cord blood lymphocytes were used as controls for each assay. A dose response with both toxoids was used to compare the CDH reaction with each in vitro assay, establishing the maximum response and threshold dose which gave a positive response. All subjects had a positive CDH response to both antigens (≥5 mm induration at 48 hr), positive DNA synthesis (stimulation index ≥3), LIF release (migration ≤80%), and lymphotoxin production, while cord blood lymphocytes were usually negative to all in vitro assays. No consistent quantitative relationships between CDH reactions and in vitro CMI responses were seen. Threshold antigen dose data revealed that DNA synthesis was approximately ten times as sensitive an assay as CDH, and 105 times as sensitive as the LIF technique. No difference in sensitivity was noted between DT and T toxoids. Three subjects re-evaluated 16 mo after the initial study showed positive CDH and CMI responses to tetanus toxoid, although the antigen dosage required varied considerably. We conclude that the CDH response with either toxoid in the concentrations used is a good indicator of CMI in the immunized individual. Although recommended starting antigen dose is given for each assay, a dose response for each assay must be performed to adequately evaluate the CMI responsiveness to a test antigen. © 1977.