Enhancement of the immunogenicity of Mycobacterium leprae peptides by means of polymerization

Abstract

Several proteins from Mycobacterium leprae have been identified as potent antigens. Segments corresponding to the primary structure of these proteins were synthesized and used for the development of a skin test for leprosy (Gutierrez et al., 1994). Here we describe the synthesis of dimers and a multiple antigenic peptide (MAP) prepared by polymerization of single peptides, and we study the potential enhancement of immunogenicity of such polymerized peptides from various M. leprae proteins: 65 kDa (P2, P15), 28 kDa (P5) and 18 kDa (P7). For the synthesis of the dimers, an extra cysteine was added either at the amino or carboxyl termini of peptides P2 and P7, whereas for P15 an extra cysteine was added only at the G-terminus. Since P5 already had a cysteine at position 2 of the amino terminus no modification was needed. For dimer formation these peptides were air-oxidized. Four different dimers were obtained for P2 and P7, and one dimer for each of P5 and P15. A MAP was prepared by combination of Pc2 and P15. From the seven peptides synthesized, only the Pc2 dimer was able to stimulate T-cell proliferation in a specific manner. None of the other dimers nor the MAP per se were capable of inducing any type of proliferation. All peptides synthesized, except the MAP, were also tested in a delayed-type hypersensitivity (DTH) assay in M. leprae immunized guinea pigs. Only P7 dimers, Pc7 and P7c, showed an increased reactivity measured by means of DTH, when compared with the parent peptide (P7). possible interpretations of these data are discussed.