Three suitable antigens for delayed-type hypersensitivity skin testing in a tropical country like Thailand

Delayed type hypersensitivity (DTH) skin test is a standard tool to assess in vivo cell-mediated immunity. Mantoux method using 4-5 common recalled antigens is recommended. However, not all antigens are widely available and appropriate antigens for tropical countries are not known. The objective of this study is to investigate what and how many antigens should be included in the DTH testing panel that suitable for Thailand and may be for this region. The DTH skin tests were done by Mantoux method in a double blinded fashion. Average induration size of > or = 5 mm defined as a positive test. Antigens included purified protein derivative (PPD), Candida albicans, tetanus toxoid (TT), Trichophyton mentagrophytes and hepatitis B vaccine (HBV). The negative control was normal saline. Of 95 healthy subjects, all showed DTH positive to > or = 1 antigen. The positivity to C. albicans, tetanus toxoid, PPD, T. mentagrophytes, and HBV was 92.6%, 83.2%, 82.1%, 50.5%, and 5.3%, respectively. When three antigens: PPD, TT and C. albicans were analyzed, 100% of subjects showed a positive response to > or = 1 antigen and 96.8% showed a positive response to > or = 2 antigens. When only PPD and TT were analyzed, 100% of subjects showed > or = 1 antigen positive and 68.4% showed both antigens positive. C. albicans antigen at 1:100 was associated with a high incidence of fever (2/20) and large local reaction (7/20), 1:500 was found to be the optimal concentration. PPD, TT and C. albicans are suitable to be included in a DTH skin testing in a tropical country like Thailand. However, in a setting where C. albicans extract is not available, testing with only two antigens of PPD and tetanus toxoid may be an alternative, but with a lower sensitivity.