Human T-cell responses in Leishmania infections

RAPD-PCR reveals genetic polymorphism among Leishmania major strains from Tunisian patients

Background

Zoonotic cutaneous leishmaniasis caused by Leishmania (L.) major is endemoepidemic in the Center and South of Tunisia. The clinical course of the disease varies widely among different patients and geographic regions. Although genetic diversity in L. major parasites has been suggested as a potential factor influencing their pathogenic variability, little information on genetic polymorphism among L. major strains is available in the literature. This work aimed to estimate the genetic variability within different isolates of L. major.

Methods

Our sample comprised 39 isolates (confirmed as L. major by restriction fragment length polymorphism typing) from patients experiencing the same clinical manifestations but living in different regions of Tunisia where L. major is endemic. Random amplified polymorphic DNA (RAPD) PCR marker polymorphism was estimated by calculating Nei and Li’s genetic distances and by an analysis of molecular variance (AMOVA).

Results

Analysis of the genetic diversity among the isolates revealed a high level of polymorphism (43 %) among them. AMOVA indicated that the highest variability (99 %) existed within the study regions.

Conclusions

Our results revealed a heterogeneous genetic profile for L. major with similar clinical manifestations occurring within the different geographical regions. Additional L. major isolates from patients, insect vectors, and reservoir hosts from different endemic foci should be collected for further analysis.

Trypanosoma cruzi infection induces differential modulation of costimulatory molecules and cytokines by monocytes and T cells from patients with indeterminate and cardiac Chagas' disease

Interactions between macrophages and lymphocytes through costimulatory molecules and cytokines are essential for mounting an efficient immune response and controlling its pathogenic potential. Here we demonstrate the immunomodulatory capacity of Trypanosoma cruzi, the causative agent of Chagas' disease, through its ability to induce differential expression of costimulatory molecules and cytokines by monocytes and T cells. Costimulatory molecule and cytokine modulation was evaluated using cells from noninfected individuals and from patients with the asymptomatic indeterminate form and those with the severe cardiac clinical form of Chagas' disease. Our results show that while exposure of monocytes to live T. cruzi leads to an increase in the frequency of CD80(+) monocytes in all groups, it decreases both the frequency and intensity of CD86 expression by monocytes from patients with the cardiac form but not from those with the indeterminate form. Conversely, exposure of lymphocytes to monocytes infected with T. cruzi increased the surface expression of cytotoxic-T-lymphocyte-associated antigen 4 (CTLA-4) by T cells from indeterminate but not from cardiac patients, compared to that from control patients. These data suggest that T. cruzi induces a potentially down-regulatory environment in indeterminate subjects, which is associated with higher CD80 and CTLA-4 expression. To test the functional importance of this modulation, we evaluated the expression of cytokines after in vitro infection. Although exposure of lymphocytes to parasite-infected monocytes induced high expression of inflammatory and anti-inflammatory cytokines by T cells in all groups, indeterminate patients displayed a higher ratio of monocytes expressing interleukin 10 than tumor necrosis factor alpha following infection than did controls. These data show the ability of T. cruzi to actively change the expression of costimulatory molecules and cytokines, suggesting molecular mechanisms for the differential clinical evolution of human Chagas' disease.

The immunology of Leishmania infection and the implications for vaccine development

Leishmania parasites are vector-borne protozoal pathogens found in tropical and subtropical regions of both the Old and New World. These parasites can cause visceral or cutaneous disease, and the pathology of the infection is determined by both host immune factors and species/strain differences of the parasite. Dogs are an important reservoir for maintaining the population of Leishmania parasites that can lead to visceral leishmaniasis in humans, and a vaccination approach may be an effective method for reducing the numbers of infected dogs. Resistance to leishmaniasis has been consistently associated with a T helper 1 immune response, characterized by the production of IFN-gamma by the antigen-specific lymphocyte population. The development of this Th1 response has been shown to be dependent upon both cytokines and dendritic cells during T cell activation. However, the development of a Leishmania vaccine effective in preventing these chronic diseases has proven to be a challenge. Vaccine trials have focused on whole-killed or subunit vaccines with adjuvants. Newer experimental strategies involve the attenuation of the Leishmania parasite via gene deletion technologies or the expression of specific Leishmania peptides within attenuated organisms, such as Bacillus Calmette Guérin. DNA vaccines and dendritic cell potentiators, such as CpG oligodeoxynucleotides and Flt-3 ligand, are also in the early stage of development. In addition, as part of blocking the transmission cycle of leishmaniasis, several laboratories are also exploring the possibility of immunomodulating the host toward the bite of the sand fly.

Leishmania infantum: soluble proteins released by the parasite exert differential effects on host immune response

The objective of this study was to analyse the modulatory effect of proteins released by cultured Leishmania infantum promastigotes on the cellular immune response of infected susceptible (BALB/c) and more resistant (C57BL/6) mice strains after 30 and 45 days of infection. One month after parasite inoculation, L. infantum released protein fractions (High, Inter, and Low according to molecular weight) stimulated C57BL/6 mice spleen cells to proliferate and to express cytokines. Following the decrease of parasite load only the Low protein fraction induced a considerable release of IL-4. In BALB/c mice, specific immune response to protein fractions was only observed at the higher parasitic level, with the fraction Inter promoting the production of IL-4 and fractions High and Low inducing high levels of IL-12. These results point out to a role of these proteins fractions in the modulation of host immunity, that depending on the host genetic background and parasite magnitude, seem to be critical in the control of parasite replication levels, thus avoiding premature host death.

Monocytes from patients with indeterminate and cardiac forms of Chagas' disease display distinct phenotypic and functional characteristics associated with morbidity

Many studies have demonstrated that monocyte-derived macrophages display critical activities in immunity to parasites. The ability of these cells to process and present antigens, produce cytokines, and provide costimulatory signals demonstrates their pivotal role in initiating immune responses. Although potential modulatory function has been attributed to monocytes from patients with Chagas' disease, a systematic phenotypic and functional analysis of these cells has not been performed. In this work, we analyzed the ex vivo expression of important surface molecules (CD11b and HLA-DR) and immunoregulatory cytokines (interleukin-10 [IL-10], IL-12 and tumor necrosis factor alpha [TNF-alpha]) in CD14(+) and CD14(-) monocytes from Chagas' disease patients with polar clinical forms of the disease: indeterminate or severe cardiac. We also evaluated the influence of in vitro infection with T. cruzi in the expression of such molecules. We observed that monocytes from indeterminate-disease patients display lower levels of HLA-DR than those from noninfected individuals both ex vivo and after in vitro infection with T. cruzi. Although ex vivo expression of CD11b was similar among the groups, in vitro infection led to decreased expression of this molecule by monocytes from Chagas' disease patients but not from noninfected individuals. Analysis of the expression of immunoregulatory cytokines showed that while monocytes from indeterminate-disease patients are committed to IL-10 expression, a higher percentage of monocytes from cardiac-disease patients express TNF-alpha after exposure to live parasites. These results suggest that monocytes from indeterminate-disease patients display modulatory characteristics related to low HLA-DR and high IL-10 expression whereas monocytes from cardiac-disease, patients may be committed to induction of inflammatory responses related to high TNF-alpha expression.

Up-regulation of Th1-type responses in mucosal leishmaniasis patients

The cytokine profile produced by peripheral blood mononuclear cells (PBMC) in response to leishmania antigens and the ability of interleukin-10 (IL-10) and transforming growth factor beta (TGF-beta) to modulate the immune response were evaluated in 21 mucosal leishmaniasis patients. Patients with mucosal disease exhibited increased gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) secretion and decreased IL-10 secretion compared to patients with classical cutaneous leishmaniasis. CD4(+) Th1 cells were the main source of IFN-gamma and TNF-alpha production in mucosal leishmaniasis patients. Evaluation of cytokine gene expression in PBMC of these patients showed that there was strong up-regulation of IFN-gamma transcripts upon stimulation with leishmania antigen, in contrast to the baseline levels of IL-10 mRNA. IL-10 suppressed IFN-gamma production by 48% in cell cultures from cutaneous leishmaniasis patients and by 86% in cell cultures from healthy subjects stimulated with purified protein derivative, whereas in similar conditions IL-10 suppressed IFN-gamma production by 19% in cell cultures from mucosal leishmaniasis patients stimulated with leishmania antigen. TGF-beta suppressed IFN-gamma levels to a greater extent in healthy subjects than in mucosal leishmaniasis and cutaneous leishmaniasis patients. These data indicate that a poorly modulated T-cell response in mucosal leishmaniasis patients leads to production of high levels of proinflammatory cytokines, such as IFN-gamma and TNF-alpha, as well as a decreased ability of IL-10 and TGF-beta to modulate this response. These abnormalities may be the basis for the pathological findings observed in this disease.

Cytotoxicity in human mucosal and cutaneous leishmaniasis

CD8+ T cells and lysis of parasitized macrophages seem to be important in the resistance to murine leishmaniasis. In the present study, we evaluated peripheral blood mononuclear cell (PBMC) from patients with either cutaneous (CL) or mucosal (ML) leishmaniasis in cell lysis assays using 51-Cr-labeled Daudi or K562 cells, or autologous antigen-pulsed macrophages as targets. Results are reported as lytic units (number of cells required for 30% lysis) per million PBMC. Exposure of patient PBMC (n = 12) to lysate from Leishmania amazonensis promastigotes led to an increase in cytotoxic activity compared to unstimulated patient cells against Daudi (81.8 +/- 14.9 vs 13.6 +/- 5 lytic units (LU) per million PBMC; mean +/- SEM) and K562 (65.7 +/- 8.4 vs 13.1 +/- 5 LU/10(6) PBMC). ML had higher responses than CL in both targets (80.4 +/- 11.0 vs 46.4 +/- 11.6 LU/10(6) PBMC for K562, and 104.3 +/- 23.8 vs 59.3 +/- 14.3 LU/10(6) PBMC for Daudi). Normal control PBMC, stimulated with L. amazonensis antigen had 6.32 +/- 3.72 LU/10(6) PBMC against Daudi cells and 9.06 +/- 2.78 LU/10(6) PBMC against K562. The cell responsible for lysis of the K562 cells was characterized as NK, by means of cell separation employing magnetic beads coupled to antibodies. Addition of recombinant TGF-beta or recombinant human IL-10 reduced L. amazonensis-induced cytotoxicity by 90% and 70%, respectively. Cytotoxicity of antigen-stimulated PBMC was also demonstrated against autologous L. amazonensis antigen-pulsed macrophages in the range of 6.7 to 41.7 LU/10(6) PBMC.(ABSTRACT TRUNCATED AT 250 WORDS)