Activated inflammatory T cells correlate with lesion size in human cutaneous leishmaniasis

Abstract

Leishmaniasis is an important parasitic disease affecting millions worldwide. In attempts to understand the clinical relevance of immunological measurements as determined using flow cytometry, several immunological phenotypes were determined for a group of well defined human leishmaniasis patients and correlated with clinical measurements of the disease (Montenegro skin test (MST) and lesion area). The analysis demonstrated a positive correlation between the MST size and the frequency of ex vivo recent activated CD4⁺ T cells. In contrast, higher frequencies of recent activated CD8⁺ T cells were correlated with a smaller MST size. Moreover, a positive correlation was observed between the lesion total area and the frequency of activated CD69⁺ (ex vivo) and CD40L⁺ (cultured with Leishmania soluble antigen (SLA)) T lymphocytes. Finally, larger lesions were also correlated with a higher frequency of SLA specific inflammatory cytokine (IFN-γ or TNF-α) producing lymphocytes. These studies demonstrate that immunological markers are correlated with clinical indicators of human leishmaniasis and serve to better understand the evolution of this important parasitic disease.

Introduction

Members of the genus Leishmania are sand fly-transmitted protozoan parasites that cause leishmaniasis in their vertebrate hosts. A large spectrum of human diseases, including localized cutaneous (CL), mucosal, and visceral leishmaniasis is caused when the amastigote forms infect and reside in phagocytic cells. The species L. braziliensis is the most frequent and widely spread Leishmania parasite in Brazil, occurring throughout the country, except north of the Amazon river. Localized cutaneous is the most common form of tegumentary leishmaniasis and the trademark of this illness is the development of single or multiple ulcerated dermal lesions, which usually respond to antimonial therapy [1].

T cell mediated immunity plays a central role in host responses to intracellular pathogens. A good prognosis for CL is related to the predominance of a Th1 response, since this leads to the production of gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α) and activation of parasite-infected macrophages [2]. Furthermore, the interaction between the surface molecules of antigen presenting cells and T cells, for example, CD40 and CD40L, may be essential for an effective immune response against intracellular parasites [3]. On the other hand, an exacerbated Th1-type response has been shown to be associated with a more severe clinical form of the disease in the case of mucosal leishmaniasis [4], and a simultaneous control of the inflammatory response is seen in human CL [5].

The relationship between specific markers of immunological activity in human leishmaniasis and clinical indicators is unknown. The delayed type hypersensitivity (DTH) test using Leishmania antigen (Montenegro skin test (MST)) is an important diagnostic method of tegumentary leishmaniasis, being largely employed in epidemiological studies for identification of exposed, healthy and cured individuals. The MST has a sensibility between 86–100% and 100% specificity [6] and has been used as an immune response and protection marker against leishmaniasis in vaccinated individuals [7]. Additionally, characteristics of ulcerated cutaneous lesions are another indicator of disease.

Thus, in the present study, the two clinical indicators related to human CL, lesion area and MST area, were correlated with several immunological indicators at the individual level in a group of 16 well-defined CL patients. All of the individuals presented with their first case of leishmaniasis, and went on to cure their disease as defined by lesion scarring in the absence of new recurrent lesions.