Peripheral blood mononuclear cells (PBMC) from
cutaneous leishmaniasis patients with ongoing Leishmania aethiopica
infection and individuals cured/under treatment from L. infantum or L. donovani
infection were stimulated in vitro with LACK, the Leishmania homologue of
receptors for activated C kinase. The LACK
protein is conserved in related leishmanial species and is expressed both in the promastigote and amastigote stages of Leishmania. Our results show that LACK induced marked NK and some CD8+ cell proliferation in PBMC from
cutaneous leishmaniasis patients with active disease. These responses were coupled with high levels of IFN-gamma and
IL-10 production. At the concentration tested, the proliferative responses to freeze-thawed Leishmania
antigen (Ft-Leish) were higher, while the levels of IFN-gamma were consistently lower than that of LACK. Although cells from individuals cured of
leishmaniasis could respond to whole Leishmania lysate by proliferation and IFN-gamma production, there was no evident response to LACK. Ethiopian controls tested at the same time also showed LACK induced proliferation with IFN-gamma and
IL-10 responses. Thus LACK reactivity in terms of proliferation and
cytokine induction were present in cells from some healthy donors and most of the patients with active lesions, while this response was absent in individuals cured of L. infantum or L. donovani
leishmaniasis. Since cure from
leishmaniasis often results in life-long protection, and active but not cured patients showed in vitro responses to LACK stimulation, questions arose as to how this highly immunodominant molecule functions during human leishmanisasis. Some possible mechanisms are discussed.