Humoral and Cellular Immune Response in Asymptomatic Dogs with Visceral Leishmaniasis: A Review.

Visceral leishmaniasis is one of the deadliest parasitic diseases in the world and affects both humans and dogs. The host immune response to Leishmania infection plays a critical role in the evolution of canine visceral leishmaniasis (CVL) and consequently in the manifestation of clinical signs. The asymptomatic form of the disease is a major concern in the diagnosis of CVL and in the transmission control of Leishmania infection. Asymptomatic dogs are found in large proportions in endemic areas and are an unquantifiable source of infection. The present review analyzes the possible relationship between the activation of the antigen-specific immune response of the host and resistance or susceptibility to CVL. The review focuses on works that address the characterization of the humoral and cellular immune response profile, at both the functional and phenotypic levels, in infected dogs. Most studies relate the absence of clinical symptomatology to an increased proliferative response and a Th1 cytokine profile. Despite the numerous findings pointing to a differential immune response in asymptomatic dogs, the contradictory results reported in this review highlight the importance of establishing a precise clinical classification of the disease, performing more longitudinal studies, and including a higher number of animals in trials.

Expression of inhibitory receptors and polyfunctional responses of T cells are linked to the risk of congenital transmission of T. cruzi.

Congenital T. cruzi infections involve multiple factors in which complex interactions between the parasite and the immune system of pregnant women play important roles. In this study, we used an experimental murine model of chronic infection with T. cruzi to evaluate the changes in the expression of inhibitory receptors and the polyfunctionality of T cells during gestation and their association with congenital transmission rate of T. cruzi infection. The results showed that pregnant naïve mice had a higher percentage of CD4+ and CD8+ T cells that expressed inhibitory receptors than cells from non-pregnant naïve mice. However, in mice chronically infected with T. cruzi, gestation induced a significant decrease in the frequency of T cells that expressed or co-expressed inhibitory receptors, as well as an increase in the frequency of polyfunctional CD4+ and CD8+ T cells. This different behavior may be due to the breakdown in the infected mice of the gestation-induced immune homeostasis, probably to control the parasite load. Remarkably, it was observed that the mothers that transmitted the parasite had a higher frequency of T cells that expressed and co-expressed inhibitory receptors as well as a lower frequency of polyfunctional parasite-specific T cells than those that did not transmit it, even though the parasitemia load was similar in both groups. All together these data suggest that the maternal immune profile of the CD4+ and CD8+ T cells could be a determining factor in the congenital transmission of T. cruzi.

Effect of secondary anchor amino acid substitutions on the immunogenic properties of an HLA-A*0201-restricted T cell epitope derived from the Trypanosoma cruzi KMP-11 protein.

The TcTLE peptide (TLEEFSAKL) is a CD8(+) T cell HLA-A*0201-restricted epitope derived from the Trypanosoma cruzi KMP-11 protein that is efficiently processed, presented and recognized by CD8(+) T cells from chagasic patients. Since the immunogenic properties of wild-type epitopes may be enhanced by suitable substitutions in secondary anchor residues, we have studied the effect of introducing specific mutations at position 3, 6 and 7 of the TcTLE peptide. Mutations (E3L, S6V and A7F) were chosen on the basis of in silico predictions and in vitro assays were performed to determine the TcTLE-modified peptide binding capacity to the HLA-A*0201 molecule. In addition, the functional activity of peptide-specific CD8(+) T cells in HLA-A2(+) chagasic patients was also interrogated. In contrast to bioinformatics predictions, the TcTLE-modified peptide was found to have lower binding affinity and stability than the original peptide. Nevertheless, CD8(+) T cells from chronic chagasic patients recognized the TcTLE-modified peptide producing TNF-α and INF-γ and expressing CD107a/b, though in less extension than the response triggered by the original peptide. Overall, although the amino acids at positions 3, 6 and 7 of TcTLE are critical for the peptide affinity, they have a limited effect on the immunogenic properties of the TcTLE epitope.

Biomarkers of therapeutic responses in chronic Chagas disease: state of the art and future perspectives.

The definition of a biomarker provided by the World Health Organization is any substance, structure, or process that can be measured in the body, or its products and influence, or predict the incidence or outcome of disease. Currently, the lack of prognosis and progression markers for chronic Chagas disease has posed limitations for testing new drugs to treat this neglected disease. Several molecules and techniques to detect biomarkers in Trypanosoma cruzi-infected patients have been proposed to assess whether specific treatment with benznidazole or nifurtimox is effective. Isolated proteins or protein groups from different T. cruzi stages and parasite-derived glycoproteins and synthetic neoglycoconjugates have been demonstrated to be useful for this purpose, as have nucleic acid amplification techniques. The amplification of T. cruzi DNA using the real-time polymerase chain reaction method is the leading test for assessing responses to treatment in a short period of time. Biochemical biomarkers have been tested early after specific treatment. Cytokines and surface markers represent promising molecules for the characterisation of host cellular responses, but need to be further assessed.

Biomarkers of therapeutic responses in chronic Chagas disease: state of the art and future perspectives

The definition of a biomarker provided by the World Health Organization is any substance, structure, or process that can be measured in the body, or its products and influence, or predict the incidence or outcome of disease. Currently, the lack of prognosis and progression markers for chronic Chagas disease has posed limitations for testing new drugs to treat this neglected disease. Several molecules and techniques to detect biomarkers in Trypanosoma cruzi-infected patients have been proposed to assess whether specific treatment with benznidazole or nifurtimox is effective. Isolated proteins or protein groups from different T. cruzi stages and parasite-derived glycoproteins and synthetic neoglycoconjugates have been demonstrated to be useful for this purpose, as have nucleic acid amplification techniques. The amplification of T. cruzi DNA using the real-time polymerase chain reaction method is the leading test for assessing responses to treatment in a short period of time. Biochemical biomarkers have been tested early after specific treatment. Cytokines and surface markers represent promising molecules for the characterisation of host cellular responses, but need to be further assessed.

The wide expansion of hepatitis delta virus-like ribozymes throughout trypanosomatid genomes is linked to the spreading of L1Tc/ingi clade mobile elements.

BACKGROUND: Hepatitis Delta Virus (HDV)-like ribozymes have recently been found in many mobile elements in which they take part in a mechanism that releases intermediate RNAs from cellular co-transcripts. L1Tc in Trypanosoma cruzi is one of the elements in which such a ribozyme is located. It lies in the so-called Pr77-hallmark, a conserved region shared by retrotransposons belonging to the trypanosomatid L1Tc/ingi clade. The wide distribution of the Pr77-hallmark detected in trypanosomatid retrotransposons renders the potential catalytic activity of these elements worthy of study: their distribution might contribute to host genetic regulation at the mRNA level. Indeed, in Leishmania spp, the pervasive presence of these HDV-like ribozyme-containing mobile elements in certain 3'-untranslated regions of protein-coding genes has been linked to mRNA downregulation. RESULTS: Intensive screening of publicly available trypanosomatid genomes, combined with manual folding analyses, allowed the isolation of putatively Pr77-hallmarks with HDV-like ribozyme activity. This work describes the conservation of an HDV-like ribozyme structure in the Pr77 sequence of retrotransposons in a wide range of trypanosomatids, the catalytic function of which is maintained in the majority.These results are consistent with the previously suggested common phylogenetic origin of the elements that belong to this clade, although in some cases loss of functionality appears to have occurred and/or perhaps molecular domestication by the host. CONCLUSIONS: These HDV-like ribozymes are widely distributed within retrotransposons across trypanosomatid genomes. This type of ribozyme was once thought to be rare in nature, but in fact it would seem to be abundant in trypanosomatid transcripts. It can even form part of the pool of mRNA 3'-untranslated regions, particularly in Leishmania spp. Its putative regulatory role in host genetic expression is discussed.