CysA2: A candidate serodiagnostic marker for Mycobacterium tuberculosis infection

Background and objective: It is important to identify and test serologically active antigens in order to devise a mixture of antigens or peptides that is most useful for serodiagnosis. This study evaluated the serodiagnostic potential of CysA2, which has not previously been described as a serological antigen, together with those of PstS1, HspX, antigen 85 complex and CFP-10 proteins. Methods: Serum IgG antibody titres against each antigen and a mixture of the antigens were measured by ELISA, in subjects with pulmonary tuberculosis and in healthy control subjects. Results: CysA2 showed diagnostic value comparable to that of PstS1 and HspX. Mixtures of these three proteins provided the highest diagnostic sensitivity. CysA2 was useful for identifying patients who did not react to HspX or PstS1, and was most valuable in increasing the sensitivity of testing. Furthermore, CysA2 efficiently overcame the limitation associated with use of PstS1, that is, significantly lower sensitivity for subjects who are negative for acid-fast bacilli. Conclusions: These findings suggest that CysA2 can be used in combination with HspX and/or PstS1 to increase the accuracy of tuberculosis diagnoses.