Cooperation between Apoptotic and Viable Metacyclics Enhances the Pathogenesis of Leishmaniasis

Mimicking mammalian apoptotic cells by exposing phosphatidylserine (PS) is a strategy used by virus and parasitic protozoa to escape host protective inflammatory responses. With Leishmania amazonensis (La), apoptotic mimicry is a prerogative of the intramacrophagic amastigote form of the parasite and is modulated by the host. Now we show that differently from what happens with amastigotes, promastigotes exposing PS are non-viable, non-infective cells, undergoing apoptotic death. As part of the normal metacyclogenic process occurring in axenic cultures and in the gut of sand fly vectors, a sub-population of metacyclic promastigotes exposes PS. Apoptotic death of the purified PS-positive (PSPOS) sub-population was confirmed by TUNEL staining and DNA laddering. Transmission electron microscopy revealed morphological alterations in PSPOS metacyclics such as DNA condensation, cytoplasm degradation and mitochondrion and kinetoplast destruction, both in in vitro cultures and in sand fly guts. TUNELPOS promastigotes were detected only in the anterior midgut to foregut boundary of infected sand flies. Interestingly, caspase inhibitors modulated parasite death and PS exposure, when added to parasite cultures in a specific time window. Efficient in vitro macrophage infections and in vivo lesions only occur when PSPOS and PS-negative (PSNEG) parasites were simultaneously added to the cell culture or inoculated in the mammalian host. The viable PSNEG promastigote was the infective form, as shown by following the fate of fluorescently labeled parasites, while the PSPOS apoptotic sub-population inhibited host macrophage inflammatory response. PS exposure and macrophage inhibition by a subpopulation of promastigotes is a different mechanism than the one previously described with amastigotes, where the entire population exposes PS. Both mechanisms co-exist and play a role in the transmission and development of the disease in case of infection by La. Since both processes confer selective advantages to the infective microorganism they justify the occurrence of apoptotic features in a unicellular pathogen

Axenic cultivation and partial characterization of Leishmania braziliensis amastigote-like stages

Leishmania braziliensis strain M2903 was adapted for growth and serially maintained as amastigotes at 34 degrees C in modified UM-54 medium, with growth curves exhibiting typical log and stationary phases. in late passages, amastigote growth took place in the absence of supplementary haemin and was unaffected when the initial medium pH was adjusted between 5.4 and 6.3. in contrast to promastigotes, which were elongated and exhibited very long free flagella endowed with the paraflagellar rod (PFR), axenic amastigotes were rounded to ovoid and displayed a short flagellum restricted to the pocket area. the absence of PFR in axenic amastigotes was confirmed in Western blots and confocal immunofluorescence microscopy, by lack of reactivity with mAb 1B10. the antibody, which specifically labelled the paraflagellar structure, recognized a 70/72 kDa doublet in Trypanosoma cruzi epimastigotes and two 70/74 kDa related proteins in L. braziliensis promastigotes. Surface I-125-labelling experiments identified promastigote-specific components (>100, 74, 45/47 and 28 kDa) and at least 1, a 76 kDa polypeptide was specific for the amastigote stage. While axenic amastigotes were agglutinated by both peanut (PNA) and Lens culinaris (LCA) agglutinins, respectively at 50 and 12.5 mu gl/l, promastigotes were not agglutinated by PNA and agglutinated in the presence of LCA at concentrations of 100 mu g/ml and higher. Axenic amastigotes infected rat bone marrow-derived macrophages and were avidly taken up by J774 cells, from which numerous organisms, able to proliferate at 34 degrees C in UM-54 medium, could be recovered 48 h later.Univ São Paulo, Inst Ciencias Biomed, Dept Parasitol, BR-05508900 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Microbiol Immunol & Parasitol, BR-04062040 São Paulo, BrazilUniversidade Federal de São Paulo, Ctr Microscopia Eletron, BR-04062040 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Microbiol Immunol & Parasitol, BR-04062040 São Paulo, BrazilUniversidade Federal de São Paulo, Ctr Microscopia Eletron, BR-04062040 São Paulo, BrazilWeb of Scienc