Glucosyltransferases (Gtfs) produced by the mutans streptococci are recognized as virulence factors in dental caries, and the inhibition of Gtfs by secretory immunoglobulin A is predicted to provide protection against this disease. The basis of such mucosal immunity is linked to the ability to reliably stimulate production of secretory immunoglobulin A against Gtfs. In this regard, we are exploring the immungenicities of various Gtf peptides genetically fused to the B subunit of cholera toxin (CTB), a known mucosal adjuvant. In this work, we have created a gene fusion linking the GtfB active-site (AS) peptide DANFDSIRVDAVDNVDADLLQIA to the amino terminus of CTB. This sequence, deduced from the nucleotide sequence of gtfB from Streptococcus mutans GS5, has been found to be strongly conserved in Gtfs from several mutans streptococci. We have purified this recombinant protein (AS:CTB) from Escherichia coli carrying the fusion gene under the control of the lactose operon promoter. This protein was immunogenic in rabbits and produced specific serum antibodies against both the Gtf peptide and the CTB moiety. The antiserum was tested for its ability to inhibit GtfB activity obtained from a mutant of S. mutans able to make only this enzyme and none of the other usual Gtfs or fructosyltransferase. Approximately 50% of the GtfB activity was inhibited in such assays. These results suggest that the AS of this enzyme is accessible to antibody binding and that this region of the protein may be considered a vulnerable target for vaccine design and development. The AS:CTB was able to bind GM 1 ganglioside in enzyme-linked immunosorbent assays, indicating that the recombinant protein retained this property, which is thought to be critical to the mucosal immunoadjuvant properties of CTB. Thus, this protein may be promising as a candidate anticaries vaccinogen alone or in combination with other Gtf peptides or conjugates. Glucosyltransferases (Gtfs) that synthesize glucan polymers from sucrose are recognized as virulence factors in smoothsurface dental decay caused by Streptococcus mutans. This was initially postulated because carious lesions were observed in experimental animals only when sucrose was included in their diets (25). The definitive role of Gtfs as virulence factors in cariogenicity was demonstrated with Gtf-deficient mutants that were created by allelic exchange (31, 48). Such mutants were reduced in cariogenicity in rat models compared with their wild-type progenitors. Typical strains of S. mutans appear to carry a repertoire of three Gtf genes, all of which contribute to maximal cariogenicity in rats (5, 7, 32, 49). In S. mutans GS5, the product of the gtfB gene synthesizes primarily a waterinsoluble glucan polymer rich in ␣-1,3-linked glucose molecules. The gtfD gene product, on the other hand, forms a water-soluble glucan composed of ␣-1,6-linked glucose molecules. The third gene, gtfC, encodes an enzyme that is able to synthesize both water-insoluble and water-soluble glucan polymers. In many wild-type strains, g...

IL-23 and IL-12 are heterodimeric cytokines which share the p40 subunit, but which have unique second subunits, IL-23p19 and IL-12p35. Since p40 is required for the development of the Th1 type response necessary for resistance to Toxoplasma gondii, studies were performed to assess the role of IL-23 in resistance to this pathogen. Increased levels of IL-23 were detected in mice infected with T. gondii and in vitro stimulation of dendritic cells with this pathogen resulted in increased levels of mRNA for this cytokine. To address the role of IL-23 in resistance to T. gondii, mice lacking the p40 subunit (common to IL-12 and IL-23) and mice that lack IL-12 p35 (specific for IL-12) were infected and their responses were compared. These studies revealed that p40−/− mice rapidly succumbed to toxoplasmosis, while p35−/− mice displayed enhanced resistance though they eventually succumbed to this infection. In addition, the administration of IL-23 to p40−/− mice infected with T. gondii resulted in a decreased parasite burden and enhanced resistance. However, the enhanced resistance of p35−/− mice or p40−/− mice treated with IL-23 was not associated with increased production of IFN-γ. When IL-23p19−/− mice were infected with T. gondii these mice developed normal T cell responses and controlled parasite replication to the same extent as wild-type mice. Together, these studies indicate that IL-12, not IL-23, plays a dominant role in resistance to toxoplasmosis but, in the absence of IL-12, IL-23 can provide a limited mechanism of resistance to this infection.

Chagas disease is caused by the protozoan Trypanosoma cruzi. The parasite reaches the secondary lymphoid organs, the heart, skeletal muscles, neurons in the intestine and esophagus among other tissues. The disease is characterized by mega syndromes, which may affect the esophagus, the colon and the heart, in about 30% of infected people. The clinical manifestations associated with T. cruzi infection during the chronic phase of the disease are dependent on complex interactions between the parasite and the host tissues, particularly the lymphoid system that may either result in a balanced relationship with no disease or in an unbalanced relationship that follows an inflammatory response to parasite antigens and associated tissues in some of the host organs and/or by an autoimmune response to host antigens. This review discusses the findings that support the notion of an integrated immune response, considering the innate and adaptive arms of the immune system in the control of parasite numbers and also the mechanisms proposed to regulate the immune response in order to tolerate the remaining parasite load, during the chronic phase of infection. This knowledge is fundamental to the understanding of the disease progression and is essential for the development of novel therapies and vaccine strategies.

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Summary In this study, we have evaluated the production of pro‐ and anti‐inflammatory cytokines and the formation of central and effector memory T cells in mice lacking mature B cells (muMT KO). The results show that Trypanosoma cruzi infection in C57Bl/6mμ MT KO mice is intensified in relation to control mice and this exacerbation is related to low levels of inflammatory cytokines produced during the acute infection and the lower numbers of central and effector memory CD4+ and CD8+ T cells generated during the acute phase of the infection. In addition, a marked reduction in the CD8+ T‐cell subpopulation was observed in muMT KO infected mice. In agreement to this, the degree of tissue parasitism was increased in muMT mice and the tissue inflammatory response was much less intense in the acute phase of the infection, consistent with a deficit in the generation of effector T cells. Flow cytometry analysis of the skeletal muscle inflammatory infiltrate showed a predominance of CD8+ CD45Rb low in B‐cell‐sufficient C57Bl/6 mice, whereas the preponderant cell type in muMT KO skeletal muscle inflammatory infiltrate was CD4+ T cells. In addition, CD8+ T cells found in skeletal muscle from muMT KO infected mice were less activated than in control B‐cell sufficient infected mice. These results suggest that B cells may participate in the generation of effector/memory T cells. In addition and more importantly, B cells were crucial in the maintenance of central and effector memory CD8+ T cell, as well as the determination of the T cell cytokine functional pattern, and they may therefore account for critical aspects of the resistance to intracellular pathogens, such as T. cruzi.