Serum immunoglobulin E against PPD antigen in patients with pulmonary tuberculosis

There is scant literature on the existence of IgE (type I allergic reactions) directed against Myocobacterium tuberculosis. To study this problem, total serum IgE (SIgE) and IgE specifically directed against the purified protein derivative of Myocobacterium tuberculosis (PPD-Sp IgE) was determined in 16 patients with AFB positive pulmonary tuberculosis (PTB) and their age and sex matched controls. Mean SIgE was significantly higher in PTB than in controls. Mild heating of the serum was necessary to detect the presence of PPD-Sp IgE which was positive in 81.3% PTB. One (6.3%) gave a class I, 9 (56.3%) gave class II and 3 (18.7%) gave class III RAST reactions. PPD-Sp IgE was absent in 3(18.7%). There were no class IV reactions. Control sera were negative for PPD-Sp IgE. Though the RAST test had a sensitivity of 80.1%, a specificity of 100% and a positive predictive value of 100%, we do not advocate this test as a diagnostic test. We have used this test to demonstrate the existence of PPD-Sp IgE and thus the existence of Type I allergic reactions against the PPD antigen of Mycobacterium tuberculosis. Its value in relation to clinical symptoms and its site of local production need further studies.