BigPatents India

The function of the PE and PPE families of proteins represented by about 10% of the coding capacity of the Mycobacterium tuberculosis genome has remained relatively unknown. We earlier described a PPE family member Rv2430c as an immunodominant antigen. We now report on another PPE family gene, Rv2608, a member of the Major Polymorphic Tandem Repeat (MPTR) subfamily, for its ability to elicit a high humoral and a low T cell response. Rv2608 was also found to be polymorphic in different clinical isolates of Mtb as determined by PCR-RFLP. 51 clinically confirn1ed TB patients belonging to three different categories, fresh infection (n=22), relapsed infection (n=21), extrapulmonary infection (n=8), and 10 healthy controls were included in the study. Recombinant Rv2608 protein showed positive reactivity with patient sera. ELISA and T cell proliferation assays with synthetic peptides corresponding to predicted regions of high antigenicity showed a predominantly humoral response in category II patients (relapsed TB). We additionally identified the Gly-X-Gly-Asn-X-Gly repeat motifs as being primarily responsible for eliciting a humoral immune response.