Endemically exposed asymptomatic individuals show no increase in the specific Leishmania (Viannia) panamensis‐Th1 immune response in comparison to patients with localized cutaneous leishmaniasis

Abstract

In Colombia, most cases of human cutaneous leishmaniasis are caused by Leishmania (Viannia) panamensis. Interestingly, up to 30% of the exposed population do not suffer from clinical leishmaniasis although it is likely that they are continuously infected with Leishmania parasites. Since it is believed that the induction of efficient Th1 immune responses protects against Leishmania infections both in humans and in animal models, we determined if endemically exposed asymptomatics showed stronger Leishmania-specific Th1 immune responses than patients with active localized cutaneous leishmaniasis (LCL). We found that Montenegro skin test responses were slightly higher among asymptomatic individuals compared to patients suffering from LCL. However, PBMC from patients with LCL showed similar Leishmania-specific proliferative responses compared to PBMC from asymptomatic individuals. Furthermore, PBMC from both groups also secreted similar amounts of IFN-gamma, IL-12p40 and IL-10 after in vitro exposure to L. panamensis. No IL-4 was detected in the supernatants. Taken together our results suggest that lack of LCL development in endemically exposed asymptomatics cannot be explained by stronger systemic anti-Leishmania Th1 immune responses or decreased Th2 responses in these individuals in comparison to individuals who develop LCL. It may be possible that other mechanisms are responsible for resistance to cutaneous leishmaniasis in Colombia in endemically exposed asymptomatics.

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

“…These analyses also showed a dominance of T lymphocytes over B lymphocytes. Using MST for diagnosis, Armijos et al [10], observed that individuals with active CL had measurably higher MST reactions than those with previous infections, while Trujillo et al [11], showed that MST responses were slightly higher in asymptomatic individuals than in patients suffering from CL. However, the Leishmaniaspecific cellular response was similar in both groups [11].…”

Th1/Th2 immune responses are associated with active cutaneous leishmaniasis and clinical cure is associated with strong interferon-γ production

“…This mixed pattern of immune response observed in patients with active lesions evolved to a Th1 response characterized by the production of IFN-␥ in cured subjects. Other studies have also reported a mixed Th1/Th2 pattern of cytokine production in cutaneous leishmaniasis [4,9]. It seems that a predominant Th1 response is necessary for parasite control and lesion healing, whereas the concomitant presence of IL-4 and IL-10, and probably other regulatory cytokines such as TGF-␤, may contribute to parasite escape, sustenance of inflammatory stimulation, and lesion persistence [9,13,14].…”

“…Simultaneous production of IFN-␥, tumor necrosis factor (TNF)-␣, and IL-10 by antigen-stimulated peripheral blood mononucleaer cells (PBMCs) from patients with active lesions [4] and IL-2, IL-4, IL-5, IL-10, and IFN-␥ mRNAs were demonstrated in biopsy samples taken from active lesions [5][6][7][8]. IL-10 expression was also significantly higher in patients who responded poorly to pentamidine treatment [5].…”

Laboratory Monitoring of Individuals with Subclinical Cutaneous Leishmaniasis Infections in Southern Brazil

“…Fagundes et al [13] found 60 individuals with subclinical infections who showed a positive Montenegro skin test, as well as one individual with a positive PCR. Trujillo et al [22] reported that about 30% of the population infected with L. (V.) panamensis did not develop clinical forms. Davies et al [12] reported a subclinical infection rate of about 10% with L. (V.) peruviana.…”