Isolation of a 33-kDa protein antigen from delipidified Mycobacterium tuberculosis H37Rv

A 33-kDa protein (TB33) was isolated from a delipidated cell sonicate (CS) of Mycobacterium tuberculosis H₃₇Rv (grown in Middlebrook 7H9 broth supplemented with glucose) using immobilized metal affinity chromatography (IMAC) on a nickel-nitrilotriacetic acid (Ni-NTA) column. TB33 could not be isolated from the culture filtrate (CF) of M. tuberculosis H₃₇Rv using Ni-NTA. TB33 was recognized by monoclonal antibodies (mAb) known to react with proteins of M. tuberculosis with a molecular mass of 33/34 kDa; namely, mAb F126-5, F67-1 and F126-2. The N-terminal amino acid sequence of TB33 was found to be Xaa-Xaa-Thr-Pro-Ala-Asp-Val-Ser/Cys-Asn-Val-Ala-Ile and thus, shows identity with the N-terminal of antigen 84 of M. tuberculosis except for two mismatches. Antibodies to TB33 could be raised in mice by administering four injections of TB33 (40 µg total protein). Sera from tuberculosis patients reacted with TB33, while those from normal healthy individuals did not.