Leishmanin skin test lymphoproliferative responses and cytokine production after symptomatic or asymptomatic Leishmania major infection in Tunisia

Abstract

Resistance to Leishmania parasite infection requires the development of a cellular immune response that activates macrophage leishmanicidal activity. In this study we have investigated the lymphoproliferative responses and in vitro cytokine production of peripheral blood mononuclear cells (PBMC) from individuals living in an endemic area for L. major infection in Tunisia. The results were compared with the DTH reaction of the leishmanin skin test (LST). Sixty-seven individuals were included in the study: 22 persons (age range 9-60 years) who developed, 2 years before the present study, a parasitologically confirmed localized cutaneous leishmaniasis (LCL) that healed spontaneously, and 45 individuals (age range 18-20 years) born and living in the same area, with no previous history of LCL. LST was positive (skin induration > or = 5 mm) in 20/22 cured cases of LCL and in 75% of healthy individuals without history of LCL. LST+ individuals expressed vigorous Leishmania-specific lymphoproliferative responses associated with in vitro production of interferon-gamma (IFN-gamma) but not IL-4. Interestingly, IL-10 was detected in parallel with the highest levels of IFN-gamma in PBMC supernatants from 3/20 cured LCL and 8/25 individuals without history of LCL. Our results showed a 98% concordance between the DTH reaction assessed by LST and the in vitro proliferative assay induced by soluble leishmanial antigens. Moreover, proliferative assays as well as cytokine analysis did not show any significant difference of the immune memory to parasite antigens developed by patients who had overt cutaneous leishmaniasis and those who had apparently asymptomatic infection.

Fig 1

In vitro lymphoproliferative responses to purified protein derivative (PPD) or soluble Leishmania major antigens (SLA) in individuals with healed localized cutaneous leishmaniasis (LCL) (group I) and from leishmanin skin test (LST)⁺ (group IIa) and LST⁻ (group IIb) individuals without a history of LCL. Each point represents an individual proliferative response expressed as Δct/min (mean count of antigen-stimulated triplicate culture − mean count of control triplicate culture).

Fig 2

Correlation between leishmanin skin test (LST) expressed as diameter of induration (mm) and lymphocyte proliferation in response to soluble Leishmania major antigens (SLA) (Δct/min). Groups are defined as in Fig. 1. •, Group I; ▵, group IIa; ▴, group IIb.

Fig 3

IFN-γ and IL-10 cytokine levels in supernatants of peripheral blood mononuclear cells (PBMC) stimulated with purified protein derivative (PPD) and soluble Leishmania major antigens (SLA). Groups are defined as in Fig. 1.