CD8 cytotoxic T cells in cutaneous leishmaniasis

CD8 cells of patients with diffuse cutaneous leishmaniasis display functional exhaustion: the latter is reversed, in vitro, by TLR2 agonists

Leishmania mexicana (Lm) causes localized (LCL) and diffuse (DCL) cutaneous leishmaniasis. DCL patients have a poor cellular immune response leading to chronicity. It has been proposed that CD8 T lymphocytes (CD8) play a crucial role in infection clearance, although the role of CD8 cytotoxicity in disease control has not been elucidated. Lesions of DCL patients have been shown to harbor low numbers of CD8, as compared to patients with LCL, and leishmanicidal treatment restores CD8 numbers. The marked response of CD8 towards Leishmania parasites led us to analyze possible functional differences between CD8 from patients with LCL and DCL. We compared IFNγ production, antigen-specific proliferation, and cytotoxicity of CD8 purified from PBMC against autologous macrophages (MO) infected with Leishmania mexicana (MOi). Additionally, we analyzed tissue biopsies from both groups of patients for evidence of cytotoxicity associated with apoptotic cells in the lesions. We found that CD8 cell of DCL patients exhibited low cytotoxicity, low antigen-specific proliferation and low IFNγ production when stimulated with MOi, as compared to LCL patients. Additionally, DCL patients had significantly less TUNEL⁺ cells in their lesions. These characteristics are similar to cellular “exhaustion” described in chronic infections. We intended to restore the functional capacity of CD8 cells of DCL patients by preincubating them with TLR2 agonists: Lm lipophosphoglycan (LPG) or Pam3Cys. Cytotoxicity against MOi, antigen-specific proliferation and IFNγ production were restored with both stimuli, whereas PD-1 (a molecule associated with cellular exhaustion) expression, was reduced. Our work suggests that CD8 response is associated with control of Lm infection in LCL patients and that chronic infection in DCL patients leads to a state of CD8 functional exhaustion, which could facilitate disease spread. This is the first report that shows the presence of functionally exhausted CD8 T lymphocytes in DCL patients and, additionally, that pre-stimulation with TLR2 ligands can restore the effector mechanisms of CD8 T lymphocytes from DCL patients against Leishmania mexicana-infected macrophages.

Leishmania mexicana causes localized and diffuse cutaneous leishmaniasis. Whereas the former is a benign form the disease, diffuse cutaneous leishmaniasis is a chronic disfiguring disease, for which no cure is available, and the immune cells of these patients respond poorly to the parasite. It has been proposed that the elimination of Leishmania-infected cells by CD8 T cells is crucial for disease control. We compared the functional characteristics of CD8 T cells from patients with localized and diffuse cutaneous leishmaniasis. We found that CD8 T cells from patients with diffuse cutaneous leishmaniasis were functionally exhausted, as compared to patients with the benign form of the disease. We were able to restore functional capacity of these cells by culturing them with molecules that stimulate TLR2. This is the first report showing that stimulation of the TLR2 can restore effector mechanisms in functionally exhausted CD8 cells from patients with diffuse cutaneous leishmaniasis. This finding will help design novel treatment schemes for patients infected with the parasite Leishmania mexicana who have the progressive, incurable form of diffuse cutaneous leishmaniasis.

CD8+ T cells as a source of IFN-γ production in human cutaneous leishmaniasis

Background

In human leishmaniasis Th1/Th2 dichotomy similar to murine model is not clearly defined and surrogate marker(s) of protection is not yet known. In this study, Th1/Th2 cytokines (IL-5, IL-10, IL-13 and IFN-γ) profile induced by purified CD4⁺/CD8⁺ T cells in response to Leishmania antigens were assessed at transcript and protein levels in 14 volunteers with a history of self-healing cutaneous leishmaniasis (HCL) and compared with 18 healthy control volunteers.

Methodology/Principal Findings

CD4⁺/CD8⁺/CD14⁺ cells were purified from peripheral blood using magnetic beads; CD4⁺/CD8⁺ T cells were co-cultured with autologous CD14⁺ monocytes in the presence of soluble Leishmania antigens (SLA). Stimulation of either CD4⁺ T cells or CD8⁺ T cells of HCL volunteers with SLA induced a significantly (P<0.05) higher IFN-γ production compared with the cells of controls. Upregulation of IFN-γ gene expression in CD4⁺ cells (P<0.001) and CD8⁺ cells (P = 0.006) of HCL volunteers was significantly more than that of controls. Significantly (P<0.05) higher fold-expression of IFN-γ gene was seen in CD4⁺ cells than in CD8⁺ cells. In HCL volunteers a significantly (P = 0.014) higher number of CD4⁺ cells were positive for intracellular IFN-γ production than CD8⁺ cells.

Conclusions/Significance

Collectively, the volunteers have shown maintenance of specific long-term immune responses characterized by a strong reaction to leishmanin skin test and IFN-γ production. The dominant IFN-γ response was the result of expansion of both CD4⁺ and CD8⁺ T cells. The results suggested that immune response in protected individuals with a history of zoonotic cutaneous leishmaniasis (ZCL) due to L. major is mediated not only through the expansion of antigen-specific IFN-γ producing CD4⁺ Th1 cells, but also through IFN-γ producing CD8⁺ T cells.

Cutaneous leishmaniasis (CL) is usually a self-healing skin lesion caused by different species of Leishmania parasite. Resistance and susceptibility of mice to Leishmania major infection is associated with two types of CD4+ T lymphocytes development: Th1 type response with production of cytokine IFN-γ is associated with resistance, whereas Th2 type response with production of cytokines IL-4 and IL-5 is associated with susceptibility. A clear Th1/Th2 dichotomy similar to murine model is not defined in human leishmaniasis and we need as much information as possible to define marker(s) of protection. We purified CD4⁺/CD8⁺ T cells, stimulated them with Leishmania antigens and analysed gene and protein expression of Th1/Th2 cytokines in volunteers with a history of self-healing CL who are presumed to be protected against further Leishmania infection. We have seen significant upregulation of IFN-γ gene expression and high IFN-γ production in the Leishmania stimulated CD4⁺ T cells and CD8⁺ T cells. We concluded that both antigen-specific IFN-γ producing CD4⁺ Th1 cells and IFN-γ producing CD8⁺ T cells contribute to the long term protection in individuals with a history of CL. This proves the importance of CD8+ T cells as a source of IFN-γ in Th1-like immune responses.

Human immunodeficiency virus and leishmaniasis

The Leishmaniases are a group of diseases transmitted to humans by the bite of a sandfly, caused by protozoan parasites of the genus Leishmania. Various Leishmania species infect humans, producing a spectrum of clinical manifestations. It is estimated that 350 million people are at risk, with a global yearly incidence of 1-1.5 million for cutaneous and 500,000 for visceral Leishmaniasis (VL). VL is a major cause of morbidity and mortality in East Africa, Brazil and the Indian subcontinent. Co-infection with human immunodeficiency virus (HIV) alters the immune response to the disease. Here we review the immune response to Leishmania in the setting of HIV co-infection. Improved understanding of the immunology involved in co-infections may help in designing prophylactic and therapeutic strategies against Leishmaniasis.

Recent developments in leishmaniasis vaccine delivery systems

BACKGROUND

The observation that recovery from infection with Leishmania confers immunity to reinfection suggests that control of leishmaniasis by vaccination may be possible. New generation vaccines, particularly those based on recombinant proteins and DNA, are found to be less immunogenic.

OBJECTIVE

There is an urgent need for the development of new and improved vaccine adjuvants.

METHODS

Based on their principal mechanisms of action, adjuvants can be broadly separated into two classes: immunostimulatory adjuvants and vaccine delivery systems. Vaccine delivery systems can carry both antigen and adjuvant for effective delivery to the antigen-presenting cells (APCs). In this article, we review the adjuvants, the delivery systems and their combinations used in the search of an effective vaccine against leishmaniasis.

CONCLUSION

Based on current knowledge, cationic liposomes appear to have better prospects as effective delivery systems for developing a vaccine for leishmaniasis.

Recent developments leading toward a paradigm switch in the diagnostic and therapeutic approach to human leishmaniasis

PURPOSE OF REVIEW

To identify recent papers showing how human and parasite genetics influence leishmaniasis, and how understanding of the immunopathology may be utilized in immunotherapy for these diseases.

RECENT FINDINGS

Progress has been made in recent years showing the complexity within populations of Leishmania spp. and indicating that different strains lead to diverse clinical pictures and responses to treatment. Thus detection of parasite genetic tags for the precise identification of infecting strains, and for predictive diagnosis of clinical and therapeutic fates seems now possible. Host genetic loci involved in disease outcome have been detected, which may also be explored for better case management. These developments in diagnosis will demand expanding the therapeutic arsenal to take their expected effect. This is starting to be fulfilled by immunotherapies successfully employed to treat cases refractory to standard first line drugs, as the result of a more profound comprehension of the immunopathology of the leishmaniases.

SUMMARY

The knowledge mounting has already helped explain why different patients present different forms of leishmaniasis and respond differently to treatment, and may be on the verge of catalyzing a major change in the already over a century old paradigm of diagnosing and managing these patients.

Mexican immunoparasitology: what is done and has to be done

In this special issue of Parasite Immunology, the reader will find reviewed some of the hottest topics in immunoparasitology, with emphasis on the most studied parasite species in Mexico. For instance, the immunological conditions that appear favorable for the survival or destruction of the parasite in the intermediate and definitive hosts in cysticercosis, as well as the use of immunodiagnostic tests in epidemiological/intervention studies are discussed in two different articles. The role that alternatively activated macrophages plays in modulating host immunity is also discussed, while in the field of Leishmaniasis, the reader will find reviewed the role that CD8+ T cells play in the host defense during the human infection. The role that antibodies may play as biomarkers of protective or pathological cellular immune events in Toxoplasma gondii infections, as well as the new insights about the regulation of the inflammatory immune response by the cytokine/chemokine network in amebiasis, are topics reviewed. The use that TSL-1 antigens may have in the development of more sensitive and specific diagnosis of human and animal trichinellosis as well as the role that the neuroimmunoendocrine network plays during schistosomiasis are also presented. We hope that our readers will find fascinating and enticing, the first ever Special Issue devoted to Mexican Immunoparasitology.