Monoclonal antibodies to 33 KD protein of Mycobacterium tuberculosis with varying epitope specificities

Five mouse monoclonal antibodies (McAb) 5D2, 5D5, 5F9, 3A8 and 3F2 against Mycobacterium tuberculosis (M. tb) 33 KD protein have been produced. All the McAbs except one were of IgG1, whereas the 3F2 was of IgM isotype. The ELISA and immunoblotting analysis show that 5D2, 5D5 and 5F9 are reactive to only 33 KD protein whereas 3A8 and 3F2 are also cross reactive to 29 KD and 29 KD + 64 KD respectively. ELISA inhibition assays using peroxidase labelled respective McAbs show that 5D2 and 5D5 recognize the same or overlapping epitopes whereas the remaining three McAbs (5F9, 3A8 and 3F2) are reactive to different epitopes of the 33 KD protein. These McAbs are cross reactive to the majority of mycobacterial strains other than M. tb including M. leprae (ML). However such reactivities may involve proteins of differing molecular sizes. Interestingly all these McAbs react to 25 KD and 29 KD of ML. The immunoreactivities of these McAbs to 33 KD appear to be directed to peptide epitopes but not to carbohydrate moiety. Both IgG and IgM antibody activities of lepromatous leprosy (L-lep) sera to 33 KD protein are heterogeneous and directed to more than 4 epitopes. The potential use of these McAbs in studying the pathomechanism of leprosy are currently being investigated.