Evidence of direct interactions between the CC-chemokines CCL3, CCL4 and CCL5 and Leishmania promastigotes

Evidence for involvement of Th17 type responses in post kala azar dermal leishmaniasis (PKDL)

Background

Post kala-azar dermal leishmaniasis (PKDL), a dermal sequel of visceral leishmaniasis, caused by Leishmania donovani, constitutes an important reservoir for the parasite. Parallel functioning of counter acting immune responses (Th1/Th2) reflects a complex immunological scenario, suggesting the involvement of additional regulatory molecules in the disease pathogenesis.

Methodology/Principal Findings

In the present study, human cytokine/chemokine/receptor specific cDNA array technique was employed to identify modulations in gene expression of host immuno-determinants during PKDL, followed by evaluation of Th17 type responses by analyzing mRNA and protein expression of Th17 markers (IL-23, IL-17, RORγt) and performing functional assays using Leishmania antigen (TSLA) or recombinant (rec)IL-17. Array analysis identified key immuno-regulatory molecules including cytokines (TNF-α, IFN-γ, IL-10, IL-17), chemokines (MCP-1, MIP-1α), apoptotic molecules (FasL, TRAIL, IRF-1) and receptors (CD40, Fas). Up regulation in lesional expression of Th17 markers was observed during PKDL compared to control (IL-17 and IL-23, P = 0.0008; RORγt, P = 0.02). In follow-up samples, chemotherapy significantly down regulated expression of all markers. In addition, lesional expression of IL-17 was confirmed at protein level by Immuno-histochemistry. Further, systemic presence of Th17 responses (IL-17 and IL-23) was observed in plasma samples from PKDL patients. In functional assays, TSLA stimulated the secretion of IL-17 and IL-23 from PBMCs of PKDL patients, while recIL-17 enhanced the production of TNF-α as well as nitric oxide (NO) in PKDL compared to control (TNF-α, P = 0.0002; NO, P = 0.0013). Further, a positive correlation was evident between lesional mRNA expression of IL-17 and TNF-α during PKDL.

Conclusion/Significance

The results highlight key immune modulators in PKDL and provide evidence for the involvement of Th17 type responses in the disease pathogenesis.

Post kala azar dermal leishamniasis (PKDL), an unusual dermatosis, develops in 5–15% of apparently cured visceral leishmaniasis cases in India and in about 60% of cases in Sudan. PKDL cases assume importance since they constitute an important human reservoir for the parasite. Host immunological responses, considered as major factors in PKDL development, are poorly understood. Limited studies have been performed to explore the host immune responses and that too, restricted to a few immune parameters. The present study employed cDNA array technique that identified various host immuno-determinants including cytokines, chemokines, apoptotic and signaling molecules which were not reported previously in PKDL. In addition, we showed for the first time that Th17 responses are present during L. donovani infection in PKDL which possibly contributes significantly to disease pathogenesis by inducing TNF-α and nitric oxide production. Our findings lead to improved understanding of the host parasite interaction in terms of immune responses and pathology in tissue lesions of PKDL.

Neutralizing endogenous chemokines with small molecules. Principles and potential therapeutic applications

Regulation of cellular responses to external stimuli such as hormones, neurotransmitters, or cytokines is achieved through the control of all steps of the complex cascade starting with synthesis, going through maturation steps, release, distribution, degradation and/or uptake of the signalling molecule interacting with the target protein. One possible way of regulation, referred to as scavenging or neutralization of the ligand, has been increasingly studied, especially for small protein ligands. It shows innovative potential in chemical biology approaches as well as in disease treatment. Neutralization of protein ligands, as for example cytokines or chemokines can lead to the validation of signalling pathways under physiological or pathophysiological conditions, and in certain cases, to the development of therapeutic molecules now used in autoimmune diseases, chronic inflammation and cancer treatment. This review explores the field of ligand neutralization and tries to determine to what extent small chemical molecules could substitute for neutralizing antibodies in therapeutic approaches.

Designing therapies against experimental visceral leishmaniasis by modulating the membrane fluidity of antigen-presenting cells

The membrane fluidity of antigen-presenting cells (APCs) has a significant bearing on T-cell-stimulating ability and is dependent on the cholesterol content of the membrane. The relationship, if any, between membrane fluidity and defective cell-mediated immunity in visceral leishmaniasis has been investigated. Systemic administration of cholesterol by liposome delivery (cholesterol liposomes) in Leishmania donovani-infected hamsters was found to cure the infection. Splenic macrophages as a prototype of APCs in infected hamsters had decreased membrane cholesterol and an inability to drive T cells, which was corrected by cholesterol liposome treatment. The effect was cholesterol specific because liposomes made up of the analogue 4-cholesten-3-one provided almost no protection. Infection led to increases in interleukin-10 (IL-10), transforming growth factor beta, and IL-4 signals and concomitant decreases in gamma interferon (IFN-gamma), tumor necrosis factor alpha, and inducible NO synthase signals, which reverted upon cholesterol liposome treatment. The antileishmanial T-cell repertoire, whose expansion appeared to be associated with protection, was presumably type Th1, as shown by enhanced IFN-gamma signals and the predominance of the immunoglobulin G2 isotype. The protected group produced significantly more reactive oxygen species and NO than the infected groups, which culminated in killing of L. donovani parasites. Therefore, cholesterol liposome treatment may be yet another simple strategy to enhance the cell-mediated immune response to L. donovani infection. To our knowledge, this is the first report on the therapeutic effect of cholesterol liposomes in any form of the disease.