Visceral leishmaniasis (VL) is a fatal disease for humans, and no vaccine is currently available. Sand fly salivary proteins have been associated with protection against cutaneous leishmaniasis. To test whether vector salivary proteins can protect against VL, a hamster model was developed involving intradermal inoculation in the ears of 100,000 Leishmania infantum chagasi parasites together with Lutzomyia longipalpis saliva to mimic natural transmission by sand flies. Hamsters developed classical signs of VL rapidly, culminating in a fatal outcome 5-6 months postinfection. Saliva had no effect on the course of infection in this model. Immunization with 16 DNA plasmids coding for salivary proteins of Lu. longipalpis resulted in the identification of LJM19, a novel 11-kDa protein, that protected hamsters against the fatal outcome of VL. LJM19-immunized hamsters maintained a low parasite load that correlated with an overall high IFN-␥/TGF-␤ ratio and inducible NOS expression in the spleen and liver up to 5 months postinfection. Importantly, a delayed-type hypersensitivity response with high expression of IFN-␥ was also noted in the skin of LJM19-immunized hamsters 48 h after exposure to uninfected sand fly bites. Induction of IFN-␥ at the site of bite could partly explain the protection observed in the viscera of LJM19-immunized hamsters through direct parasite killing and/or priming of anti-Leishmania immunity. We have shown that immunity to a defined salivary protein (LJM19) confers powerful protection against the fatal outcome of a parasitic disease, which reinforces the concept of using components of arthropod saliva in vaccine strategies against vector-borne diseases.antisaliva immunity ͉ Leishmania ͉ sand fly saliva ͉ vector-based vaccine

Epidemiologic aspects of the relationship between infection with Leishmania chagasi and development of clinical visceral leishmaniasis (VL) were studied in all children < 11 years old in a defined, endemic, rural area of the state of Ceará in northeast Brazil. Antileishmanial antibodies were measured in the same subjects by ELISA on six occasions between May 1987 and August 1989. Seroconversion was documented during this period in 108 children, with a cumulative annual incidence of 4.6%. Twelve (11.1%) of these children developed VL. Age < 4 years, hematocrit < 33%, and living in the mountains predicted the development of clinically apparent VL after seroconversion. Despite a high percentage of dogs serologically positive in the region (38%), there was no increased risk of infection for children living in the same household with dogs. Since children in households with a prior case of VL had a threefold increased risk of infection, human-sandfly-human transmission might have been important.

No abstract

Saliva of bloodfeeding arthropods has been incriminated in facilitating the establishment of parasite in their host. We report on the leukocyte chemoattractive effect of salivary gland homogenate (SGH) from Lutzomyia longipalpis on saliva-induced inflammation in an air pouch model. SGH (0.5 pair/animal) was inoculated in the air pouch formed in the back of BALB/c or C57BL/6 mice. L. longipalpis SGH induced a significant influx of macrophages in BALB/c but not in C57BL/6 mice. SGH-induced cell recruitment reached a peak at 12 h after inoculation and was higher than that induced by the LPS control. This differential cell recruitment in BALB/c mice was directly correlated to an increase in CCL2/MCP-1 expression in the air pouch lining tissue. In fact, treatment with bindarit, an inhibitor of CCL2/MCP-1 synthesis, and also with a specific anti-MCP-1 mAb resulted in drastic reduction of macrophage recruitment and inhibition of CCL2/MCP-1 expression in the lining tissue. CCL2/MCP-1 production was also seen in vitro when J774 murine macrophages were exposed to L. longipalpis SGH. The SGH effect was abrogated by preincubation with serum containing anti-SGH IgG Abs as well as in mice previously sensitized with L. longipalpis bites. Interestingly, the combination of SGH with Leishmania chagasi induced an increased recruitment of neutrophils and macrophages when compared with L. chagasi alone. Taken together these results suggest that SGH not only induces the recruitment of a greater number of macrophages by enhancing CCL2/MCP-1 production but also synergizes with L. chagasi to recruit more inflammatory cells to the site of inoculation.

Crucial to the defense against leishmaniasis is the ability of the host to mount a cell-mediated immune response capable of controlling and/or eliminating the parasite. Cell recruitment to the site of infection is essential to the development of the host cellular immune response. The process is controlled by chemokines, which are chemotactic cytokines produced by leukocytes and tissue cells.

The occurrence and antimicrobial resistance pattern of Shigella isolates obtained from persons in community and hospital-based studies of diarrhea and matched controls in northeastern Brazil were studied. The isolation rate of Shigella spp. from patients with diarrhea during 1988 to 1993 varied from 4.5% (26 of 575) for the urban community of Gonçalves Dias to 6.7% (12 of 179) and 5.9% (7 of 119) for Hospital Infantil and Hospital Universitário, respectively. Of the 55 Shigella isolates (45 from patients with diarrhea, 8 from controls, and 2 undetermined) 73% (40 of 55) were Shigella flexneri, 16% (9 of 55) were S. sonnei, 7% (4 of 55) were S. boydii, and 4% (2 of 55) were S. dysenteriae. Of 39 S. flexneri strains, over half were resistant to ampicillin, trimethoprim-sulfamethoxazole, or both. Over 64% were resistant to streptomycin, chloramphenicol, and tetracycline. Overall, 82% of all S. flexneri isolates were resistant to four or more antimicrobial agents tested. As elsewhere, in the northeast of Brazil, ampicillin and trimethoprim-sulfamethoxazole are no longer reliable for treatment of S. flexneri infection. Most Shigella strains were resistant to four or more antimicrobial agents. Nalidixic acid was still useful for treatment of infections due to S. flexneri.

In the present study we evaluated Canavalia brasiliensis (ConBr), Pisum arvense (PAA) and Artocarpus integrifolia (KM+) lectins as immunostimulatory molecules in vaccination against Leishmania amazonensis infection. Although they induced IFN-gamma production, the combination of the lectins with SLA antigen did not lead to lesion reduction. However, parasite load was largely reduced in mice immunized with KM+ lectin and SLA. KM+ induced a smaller inflammatory reaction in the air pouch model and was able to inhibit differentiation of dendritic cells (BMDC), but to induce maturation by enhancing the expression of MHC II, CD80 and CD86. These observations indicate the modulatory role of plant lectins in leishmaniasis vaccination may be related to their action on the initial innate response.

The initial encounter of Leishmania cells and cells from the immune system is fundamentally important in the outcome of infection and determines disease development or resistance. We evaluated the anti-Leishmania amazonensis response of naive volunteers by using an in vitro priming (IVP) system and comparing the responses following in vivo vaccination against the same parasite. In vitro stimulation allowed us to distinguish two groups of individuals, those who produced small amounts of gamma interferon (IFN-γ) (n = 16) (low producers) and those who produced large amounts of this cytokine (n = 16) (high producers). IFN-γ production was proportional to tumor necrosis factor alpha and interleukin 10 (IL-10) levels but did not correlate with IL-5 production. Volunteers who produced small amounts of IFN-γ in vitro remained low producers 40 days after vaccination, whereas high producers exhibited increased IFN-γ production. However, 6 months after vaccination, all individuals tested produced similarly high levels of IFN-γ upon stimulation of their peripheral blood mononuclear cells with Leishmania promastigotes, indicating that low in vitro producers respond slowly in vivo to vaccination. In high IFN-γ producers there was an increased frequency of activated CD8+ T cells both in vitro and in vivo compared to the frequency in low producers, and such cells were positive for IFN-γ as determined by intracellular staining. Such findings suggest that IVP responses can be used to predict the pace of postvaccination responses of test volunteers. Although all vaccinated individuals eventually have a potent anti-Leishmania cell-mediated immunity (CMI) response, a delay in mounting the CMI response may influence resistance against leishmaniasis