Sandra Regina Afonso Cardoso; João Carlos França da Silva; Roberto Teodoro da Costa; Wilson Mayrink; Maria Norma Melo; Marilene Suzan Marques Michalick; Ibrahim Afrânio Willi Liu; Ricardo Toshio Fujiwara; Evaldo Nascimento
Departamento de Parasitologia do Instituto de Ciências Biológicas da Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil
ABSTRACT
Immunogenic proteins from nonliving promastigote polyvalent Leishmania vaccine against American tegumentary leishmaniasis (Leishvacin®), produced by Biobrás (Biochemistry of Brazil ), Montes Claros, State of Minas Gerais, Brazil, were identified and purified by polyacrylamide electrophoresis gel and electroelution. C57BL/10 mice were vaccinated with proteins with estimated molecular weights of 42, 46, 63, 66, 73, 87, 97, and 160kDa in three doses of 30µg of each protein at 15-day intervals combined with 250µg of Corynebacterium parvum followed by a challenge infection with 105 infective promastigotes from Leishmania (Leishmania) amazonensis. The ability of these proteins to induce immune response and protection was analyzed. No statistical difference was observed in the level of IFN-g induced by proteins in vaccinated groups in comparison with control groups. Six months after challenge infection, protection levels of 28.57; 42.86; 57.14; 42.86; 42.86, 57.14; 42.86 and 57.14% were demonstrated for each purified protein.
Key-words:Tegumentary leishmaniasis. immunogenic proteins. Leishvacin®.
RESUMO
Proteínas imunogênicas da vacina polivalente de promastigotas mortas de leishmanias (Leishvacin®) produzida pela Biobrás Bioquímica do Brasil, Montes Claros, Minas Gerais, Brasil foram identificadas e purificadas por eletroforese em gel de poliacrilamida e eletroeluição. Camundongos C57BL/10 foram vacinados com proteínas de pesos moleculares estimados em 42, 46, 63, 66, 73, 87, 97 e 160kDa em três doses de 30µg de cada proteína combinada com 250µg de Corynebacteriumparvum em intervalos de 15 dias e desafiados com uma infecção desafio de 105 promastigotas infectantes de Leishmania (Leishmania) amazonensis na base da cauda. Foram avaliadas a habilidade dessas proteínas em induzir resposta imune e proteção dos animais vacinados após a infecção desafio. Nenhuma diferença estatística foi observada nos níveis de IFN-gnos grupos vacinados em comparação ao grupo controle. Proteção de 28,57; 42,86; 57,14; 42,86; 42,86, 57,14; 42,86; 57,14% foi demonstrado para cada proteína.
Palavras-chaves: Leishmaniose tegumentar. proteínas imunogênicas. Leishvacin®.
American tegumentary leishmaniasis (ATL) is a disease caused by different species of Leishmania, which constitutes an important public health problem in Latin America9. The disease affects people living in a variety of ecological settings, including primary rain forest as well as agricultural and urban areas. Even without considering under-reporting and the large number of incorrect diagnoses, the estimated prevalence is high and incidence of American cutaneous leishmaniasis has increased as a consequence of environmental changes and difficulties in controlling the vectors and reservoirs.
Protective immunity against leishmaniasis is largely mediated by T cells3 7 14 15. The nature of the host immune response to different Leishmania infections is one of the main factors controlling the outcome of the disease. In mice, susceptibility and resistance to L. major have been correlated with selective stimulation of the CD4+ cell subsets, Th1 and Th2, and the type of cytokines that they produce4 31. In general, a protective role is associated with the cells of the Th1 subset that secrete IL-2 and IFN-g, whereas the expansion of cells of Th2 subset, which produce IL-4 and IL-10, exacerbates disease12 29 30 31 32. Similarly to the L. major in Balb/c30, treatment of Balb/c mice with anti-IL-4 monoclonal antibodies abrogates its susceptibility to L. amazonensis6. In addition, in vitro and in vivo studies indicate that IL-121 6 and tumor necrosis factor a (TNF-a) are also crucial to the establishment of resistance against experimental leishmaniasis33.
Efforts to develop a vaccine to control ATL have been made by several laboratories. Different vaccine compositions including crude and purified Leishmania components have been tested in animal models as well as in human vaccination trials. In Brazil, the development of a non-living promastigote vaccine against ATL was initiated by Pessoa’s group in the decade of 194025 26, followed by the first publication by Mayrink’s group in 197919. Significant progresses were made in several clinical trials demonstrating the immunogenicity of the vaccine, such as: (a) induction of a delayed-type hypersensitivity, as demonstrated by a positive skin test19; (b) no appreciable side effects21; (c) conversion of delayed-type hypersensitivity with a statistically significant level of protection compared with non-converted or non-vaccinated subjects2 27; (d) old vaccine preparations (four years old) proved to be equivalent to newly prepared ones in converting the results of skin tests from negative to positive as well as providing protection21; (e) protection of 50% of vaccinated individuals whose skin test converted from negative to positive after vaccination2; (f) strong correlation has been found between positive skin test results and lymphocyte stimulation indices (LSI) in vaccinated subjects24; (g) LSIs of vaccinated groups were significantly higher (P<0.001) than those of placebo group26; (h) eight major antigens with estimated molecular weights of 13.5 to 160kDa may play an important role in the immunity against tegumentary leishmaniasis24; (i) gp63 was the major protein present in our vaccine24; and (j) T lymphocyte-mediated immune response against Leishmania antigens, by Th1 profile response and by protection against the disease, was observed in 50% of subjects vaccinated2 8 19 21 22 24.
This vaccine has become an important tool in the identification of the key parasite antigens that induce immunity against tegumentary leishmaniasis, and has also been successfully used as an immunotherapeutic agent20 18.
In this study, we isolated proteins of estimated molecular weight of 42, 46, 63, 66, 73, 87, 97 and 160kD from Leishvacin®, by preparative polyacrylamide gel electrophoresis, and tested their ability to induce IFN-g synthesis by T lymphocytes from vaccines. We also analyzed the ability of these isolated proteins to induce protective immunity in susceptible C57BL/10 mice against L. (L.) amazonensis.
MATERIAL AND METHODS
Leishvacin®. Leishvacin® was produced and supplied by BioBrás (Biochemistry of Brazil), according to Mayrink’s group methodology of production21 in GMP (good manufacturing practice) conditions. It is constituted by five Leishmania stocks: (Leishmania (Leishmania) amazonensis MHOM/BR/60/BH6, Leishmania major-like, MHOM/BR/73/BH121, Leishmania major-like MHOM/BR/71/BH49, Leishmania (Leishmania) amazonensis IFLA/BR/67/PH8, Leishmania (Viannia) braziliensis MHOM/BR/70/M117619 24). Proteins from Leishvacin® were isolated on 10% SDS-PAGE14. The proteins were electroeluted from gel slices, dialyzed against PBS pH 7.2, concentrated and dialyzed again in the same buffer. Protein concentrations were determined according to Lowry’s method16.
C57BL/10 mice. Isogenic female mice aged 8-10 weeks were used in the vaccination experiments. These animals were maintained in the animal house of the Federal University of Minas Gerais, State of Minas Gerais, Brazil, under US National Institutes of Health guidelines for animal care.
Mice vaccination. Eight groups of seven 8-10 week mice, obtained from animal facilities at Federal University of Minas Gerais, Minas Gerais State, Brazil, were vaccinated subcutaneously into the left footpad with three doses of each identified and purified protein (30mg) at 15-day intervals combined with 250mg of live CP (Corynebacterium parvum Fundação Athaulpho de Paiva, Rio de Janeiro, Brazil), as adjuvant. Three control groups with seven animals each received only 250mg of live CP, 100ml of PBS (phosphate buffer saline) or 100mg of Leishvacin® in 100ml of PBS, respectively, following the same immunization scheme.
Parasite for challenge infection. The L. (L.) amazonensis IFLA/BR/67/PH8 strain was used for experimental infections. This strain was maintained by continuous passages in hamsters for the preparation of infective promastigotes. Promastigotes were washed in 0.8% NaCl solution and 105stationary phase promastigotes of L. amazonensis were used in the challenge infection for each C57BL/10 mice. The injection was done into the base of the tail, seven days after the last vaccination. The development of lesions was monitored at 15-day intervals for 180 days.
Lymphocyte stimulation index (LSI). Six months after challenging the animals, they were sacrificed and the spleens were transferred to Petri dishes containing complete RPMI 1640 medium (Gibco, USA), as previously described23.
Interferon gamma assay (IFN-g). Spleen cells were obtained from C57BL/10 mice of each vaccinated group, as well as control mice at six months after challenge infection. Cells were prepared as previously described11. Cells were isolated by Ficoll-hypaque gradient centrifugation and suspended at 1.5 x 106cells per ml in complete RPMI 1640 medium (200mM L-glutamine, 100UI of penicillin per ml, 50mg of streptomycin per ml, 10mM HEPES [N-2-hydroxyethylpiperasine-N-2-ethanesulfonic acid]) containing 10% inactivated fetal calf sera (FBS). Cell culture was carried out in flat-bottomed 24-well plates and maintained at 37oC in a 5% CO2incubator for two days. The IFN-g measurement was performed by ELISA on supernatant pools of triplicate cultures stimulated with each protein (20mg/ml), Leishvacin® (50µg/ml) and Corynebacterium parvum (50µg/ml) at 48 hours after stimuli. Results are presented as means of cytokine concentrations (UI/ml) determined for seven vaccinated individuals in each group.
Vaccine efficacy. Clinical observations of the animals and lesion development were carried out during 180 days after the challenge infections at seven-day intervals. Lesion measurements were done at 15-day intervals using a micrometer (Mitutoyo Sul Americana, São Paulo, Brazil). The results were expressed as percentages of protection, which represent the animals without lesions per group. The animals were sacrificed and smears from footpad skin were Giemsa stained for the presence of parasites. For histopathological examinations a biopsy was taken at the site of infection fixed in 10% formalin in PBS, washed in water for 4 hours, dehydrated and embedded in paraffin, cut (3-4mm thick) and stained with hematoxylin and eosin for optical microscopic examination35.
Statistical analysis. Statistical significance was determined by Pearson chi-square test, Student t test10, and Statistical Epinfo analysis version 6.0.
RESULTS
Eight proteins with estimated molecular weights of 42, 46, 63, 66, 73, 87, 97 and 160kD were purified from Leishvacin® (Figure 1A,B).
All proteins were tested in vitro to stimulate peripheral blood monocyte cells (PBMC) from vaccinated mice in order to determine their ability to induce synthesis of IFN-g. The results showed that the levels of IFN-g, produced by protein stimulation in culture supernatants, were not statistically significant (P>0.05) ranging from 19.8UI/ml to 15.8UI/ml (Table 1). The levels of IFN-g induced by each protein were comparable to those induced by Leishvacin®. These proteins were also able to induce cell proliferation and no statistically significant differences were observed between them with regard to the amplitude of proliferation induced (Table 1).
Vaccination of C57BL/10 mice with each of these purified proteins resulted in different levels of protection, as shown in Table 2. Lesion development was followed over a period of 180 days after challenge with 105 promastigotes of L. amazonensis. Non-vaccinated mice that received only C. parvum developed progressive infections on the footpads. The proteins of 63, 87 and 160kD induced protection of 4/7 (57.14%) mice, similar to the protection obtained with Leishvacin®. Protective rates of 3/7 (42.86%) mice were obtained by those animals vaccinated with proteins of 46, 66, 73 and 97kD. The protein of 42kD induced protection of only 2/7 (28.57%) mice. In the other two control groups, all animals were infected.
Good correlation was found between protection and LSI in the groups immunized with the purified proteins and in the group immunized with Leishvacin®, in comparison with the other control groups (only CP and PBS). Such data could be observed for the proteins of 46, 63, 66, 87, 97 and 160kD, whereas the 42kD proteins produced only a slight protective effect (Table 1).
The presence of parasites in the footpad lesions of all mice was evaluated by histopathological studies involving serial sections of the footpad tissue. No parasites were found in vaccine-protected mice, while in the non-vaccinated ones parasites were observed inside macrophages or among the cells. Amastigote forms were found through histopathological examination in the control groups (Figure 2).
DISCUSSION
In this study, we demonstrated that eight proteins, isolated from Leishvacin®, induced synthesis of IFN-g by lymphocyte from vaccinated mice and induced lymphocyte proliferation in vaccinated animals. Previous studies have shown that human individuals vaccinated with Leishvacin®developed Leishmania-specific T cell responses and protective immunity against this parasite. Characterization of cytokine production and lymphocyte phenotype involved in this immune response indicated that PBMC from vaccinated subjects induced IFN-g but not IL-422. Moreover, in subjects vaccinated one year before, CD8+ T cells proliferated preferentially in response to L. (V.) braziliensis antigen22.
Different levels of protection were observed in C57BL/10 mice vaccinated with each protein. C57BL/10 mice are resistant to L. major, but susceptible to L. amazonensis infection, developing a chronic infection31. A polarized Th1 response is detected after L. major infection, but this response is absent following L. amazonensis infection, indicating that parasite-associated factors are able to modify the T helper response profile induced in C57BL/10 mice30.
Characterization of the immune response associated with experimental murine leishmaniasis has led to the identification of two immunoregulatory subsets of T helper lymphocytes (Th1 and Th2) that influence the outcome of infection. Th1 lymphocytes and synthesis of IFN-g and IL-2 are associated with mild or self-healing disease, whereas the expansion of IL-4- and IL-10-producing Th2 lymphocytes is associated with disseminated infection31. A similar distinction has been observed in patients with different disease manifestations. T cells present in lesions of patients with localized and self-healing cutaneous leishmaniasis predominantly secrete IFN-g and other Th1 cytokines, but not IL-45 27 31. CD8+ T cells also synthesized IFN-g, even though the protective role of these cells in leishmaniasis is not completely clear. The analysis of in vitro IFN-g production in response to purified antigens therefore provides a reliable parameter for the ranking of immunodominant antigens.
Among the eight proteins evaluated, gp46 and gp63 have already received considerable attention and are known to induce protective immunity in susceptible mice, as well as synthesis of IFN-g. Furthermore, in a previous report, C57BL/10 mice were immunized with purified proteins from L. (L.) amazonensis and showed an induction of a protective immunity and an elevated synthesis of IFN-g by spleen cells, suggesting a protection against the parasite23.
However, in our study, no positive correlation between levels of IFN-g and protection was found. In addition, the amounts of IFN-g production observed in susceptible mice were equivalent to the levels induced by Leishvacin®. This result also indicates a positive correlation between proliferation response and protection. These proteins are Leishmania immunodominant antigens and also important components of Leishvacin®.
We must consider, however, that each protein fraction evaluated in this study may consist of a mixture of different proteins. Leishvacin® is composed of five different stocks of Leishmania, made from different species. Although high levels of homology may exist among them, the presence of immunossupressive protein or epitopes cannot be ruled out24. Therefore, further studies are required to investigate the immunogenic potential of these proteins isolated from the Leishmania strains that comprise Leishvacin®.
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Recebido para publicação em 11/3/2002
Supported by CAPES, PADCT/CNPq/Biotechnology, Grant # 62.0252/91.0
Address to: Dr. Evaldo Nascimento. Depto de Parasitologia/ICB/UFMG. Antonio Carlos 6627, Pampulha, 31270-901 Belo Horizonte, Minas Gerais, Brazil.
Fax: 55 31-3499-2859
e-mail: evaldo@icb.ufmg.br
