Tetanus toxoid skin test in children: Correlation with in vitro lymphocyte stimulation and monocyte chemotaxis

Abstract

To determine if skin testing with tetanus toxoid (2 Lf/ml) can be used to assess cellular immunity, skin tests were performed on 64 healthy immunized controls, nine unimmunized infants, and seven patients with agammaglobulinemia with intact cellular immunity. Induration of 5 mm of diameter or greater at 48 hours was considered a positive response. The tetanus skin test response was correlated with the patient's age, number of prior tetanus immunizations, tetanus antibody titer, in vitro lymphocyte stimulation index to tetanus toxoid, and monocyte chemotaxis. None of the nine unimmunized infants, 4/7 (57%) of the patients with agammaglobulinemia, and 38/64 (59%) of the immunized subjects had positive skin tests. Positive tetanus skin tests were correlated with number of DPT immunizations (31 of 39 with 4 DPTs had a positive skin test) and age (7 of 24 under age 2 had a positive skin test, and 31/40 over age 2 had a positive skin test). In both younger and older subjects, positive tetanus skin tests were correlated with monocyte chemotaxis. By contrast, there was little correlation of the skin test with the tetanus antibody titer. Nearly all (60/64 [94%]) of the immunized controls had a positive in vitro lymphocyte stimulation; the magnitude of the response was significantly correlated with the tetanus skin test in younger (<age 2) but not in older subjects. These results indicate that tetanus toxoid skin testing is a safe, readily available method to assess cellular immunity, is probably independent of tetanus antibody, but is less sensitive than in vitro stimulation. A positive tetanus skin test implies intact cellular immunity and, indirectly, intact monocyte chemotaxis.