Recombinant Listeria monocytogenes as a live vaccine vehicle for the induction of protective anti-viral cell-mediated immunity.

Listeria monocytogenes (LM) is a Gram-positive bacterium that is able to enter host cells, escape from the endocytic vesicle, multiply within the cytoplasm, and spread directly from cell to cell without encountering the extracellular milieu. The ability of LM to gain access to the host cell cytosol allows proteins secreted by the bacterium to efficiently enter the pathway for major histocompatibility complex class I antigen processing and presentation. We have established a genetic system for expression and secretion of foreign antigens by recombinant strains, based on stable site-specific integration of expression cassettes into the LM genome. The ability of LM recombinants to induce protective immunity against a heterologous pathogen was demonstrated with lymphocytic choriomeningitis virus (LCMV). LM strains expressing the entire LCMV nucleoprotein or an H-2Ld-restricted nucleoprotein epitope (aa 118-126) were constructed. Immunization of mice with LM vaccine strains conferred protection against challenge with virulent strains of LCMV that otherwise establish chronic infection in naive adult mice. In vivo depletion of CD8+ T cells from vaccinated mice abrogated their ability to clear viral infection, showing that protective anti-viral immunity was due to CD8+ T cells.

Autoimmunity in Chagas disease cardiopathy: biological relevance of a cardiac myosin-specific epitope crossreactive to an immunodominant Trypanosoma cruzi antigen.

Heart tissue destruction in chronic Chagas disease cardiopathy (CCC) may be caused by autoimmune recognition of heart tissue by a mononuclear cell infiltrate decades after Trypanosoma cruzi infection. Indirect evidence suggests that there is antigenic crossreactivity between T. cruzi and heart tissue. As there is evidence for immune recognition of cardiac myosin in CCC, we searched for a putative myosin-crossreactive T. cruzi antigen. T. cruzi lysate immunoblots were probed with anti-cardiac myosin heavy chain IgG antibodies (AMA) affinity-purified from CCC or asymptomatic Chagas disease patient-seropositive sera. A 140/116-kDa doublet was predominantly recognized by AMA from CCC sera. Further, recombinant T. cruzi protein B13--whose native protein is also a 140- and 116-kDa double band--was identified by crossreactive AMA. Among 28 sera tested in a dot-blot assay, AMA from 100% of CCC sera but only 14% of the asymptomatic Chagas disease sera recognized B13 protein (P = 2.3 x 10(-6)). Sequence homology to B13 protein was found at positions 8-13 and 1442-1447 of human cardiac myosin heavy chain. Competitive ELISA assays that used the correspondent myosin synthetic peptides to inhibit serum antibody binding to B13 protein identified the heart-specific AAALDK (1442-1447) sequence of human cardiac myosin heavy chain and the homologous AAAGDK B13 sequence as the respective crossreactive epitopes. The recognition of a heart-specific T. cruzi crossreactive epitope, in strong association with the presence of chronic heart lesions, suggests the involvement of crossreactivity between cardiac myosin and B13 in the pathogenesis of CCC.