Immunization against full-length protein and peptides from the Lutzomyia longipalpis sand fly salivary component maxadilan protects against Leishmania major infection in a murine model

Leishmaniasis is an arthropod vectored disease causing considerable human morbidity and mortality. Vaccination remains the most realistic and practical means to interrupt the growing number and diversity of sand fly vectors and reservoirs of Leishmania. Since transmission of Leishmania is achieved exclusively by sand fly vectors via immune-modulating salivary substances, conventional vaccination requiring an unmodified host immune response for success are potentially destined to fail unless immunomodulatory factors are somehow neutralized. Using cationic liposome DNA complexes (CLDC) as an adjuvant system along with Lu. longipalpis sand fly salivary component maxadilan (MAX) as antigen (Ag), we show that mice are protected from the MAX-induced exacerbation of infection with Leishmania major (Lm). The CLDC adjuvant and alum were comparable in terms of lesion induration and decreased parasite burden, however the alum adjuvant imposed more inflammation at the injection site. BALB/c, C3H and C57BL/6 mice vaccinated with MAX-CLDC containing either the full-length MAX or peptides spanning the N- and C-terminal regions of MAX are protected against footpad challenges with Lm co-injected with MAX. When compared to unvaccinated controls, all strains of mice immunized with CLDC containing either peptides encompassing the first 20 N-terminal AA or those spanning the last 15 AA of the C-terminal domain of MAX demonstrated decreased parasite burden after 9 or 18 weeks post challenge with Lm + MAX. MAX-CLDC immunized mice showed increased IFNγ-secreting and decreased IL-4-secreting CD4⁺ cells in footpad-draining lymph nodes. Antisera from C-terminal peptide (P11) MAX-CLDC-vaccinated animals was capable of recognizing FL-MAX and its C-terminal domain and also blocked MAX-mediated reprogramming of bone marrow-derived dendritic cells (BM-DC) in vitro. This peptide vaccine targeting sand fly MAX, improves host immunity against MAX-mediated immunomodulation.

Local suppression of T cell responses by arginase-induced L-arginine depletion in nonhealing leishmaniasis

The balance between T helper (Th) 1 and Th2 cell responses is a major determinant of the outcome of experimental leishmaniasis, but polarized Th1 or Th2 responses are not sufficient to account for healing or nonhealing. Here we show that high arginase activity, a hallmark of nonhealing disease, is primarily expressed locally at the site of pathology. The high arginase activity causes local depletion of L-arginine, which impairs the capacity of T cells in the lesion to proliferate and to produce interferon-γ, while T cells in the local draining lymph nodes respond normally. Healing, induced by chemotherapy, resulted in control of arginase activity and reversal of local immunosuppression. Moreover, competitive inhibition of arginase as well as supplementation with L-arginine restored T cell effector functions and reduced pathology and parasite growth at the site of lesions. These results demonstrate that in nonhealing leishmaniasis, arginase-induced L-arginine depletion results in impaired T cell responses. Our results identify a novel mechanism in leishmaniasis that contributes to the failure to heal persistent lesions and suggest new approaches to therapy.

Leishmania parasites are obligate intracellular pathogens that predominantly invade macrophages. Instruction of macrophages by T cell-derived signals is required to control parasite growth. Here we show that arginase, an enzyme induced in Leishmania-infected macrophages, is highly expressed at the site of pathology in nonhealing lesions and causes local depletion of L-arginine, an amino acid that is essential for efficient T cell responses. This local reduction in L-arginine impairs the capacity of T cells in the lesion to proliferate and to produce interferon-γ, one of the signals required for parasite killing. Cure of Leishmania infection by drug treatment is accompanied by a reduction in arginase activity and restoration of T cell effector functions. Furthermore, inhibition of arginase, as well as injection of L-arginine, reverses immunosuppression and results in more efficient control of parasite replication. Our results identify a novel mechanism accounting for ineffective T cell responses in nonhealing leishmaniasis.

Lutzomyia longipalpis salivary peptide maxadilan alters murine dendritic cell expression of CD80/86, CCR7, and cytokine secretion and reprograms dendritic cell-mediated cytokine release from cultures containing allogeneic T cells

Leishmania protozoan parasites, the etiologic agent of leishmaniasis, are transmitted exclusively by phlebotomine sand flies of the genera Phlebotomus and Lutzomyia. In addition to parasites, the infectious bite inoculum contains arthropod salivary components. One well-characterized salivary component from Lutzomyia longipalpis is maxadilan (MAX), a vasodilator acting via the type I receptor for the pituitary cyclic AMP activating peptide. MAX has been shown to elicit immunomodulatory effects potentially dictating immune responses to Leishmania parasites. When exposed to MAX, both resting and LPS-stimulated dendritic cells (DCs) show reduced CD80 and CD86 expression on most DCs in vitro. However, CD86 expression is increased significantly on a subpopulation of DCs. Furthermore, MAX treatment promoted secretion of type 2 cytokines (IL-6 and IL-10) while reducing production of type 1 cytokines (IL-12p40, TNF-alpha, and IFN-gamma) by LPS-stimulated DCs. A similar trend was observed in cultures of MAX-treated DCs containing naive allogeneic CD4(+) T cells: type 2 cytokines (IL-6 and IL-13) increased while type 1 cytokines (TNF-alpha and IFN-gamma) decreased. Additionally, the proinflammatory cytokine IL-1beta was increased in cultures containing MAX-treated mature DCs. MAX treatment of LPS-stimulated DCs also prevented optimal surface expression of CCR7 in vitro. These MAX-dependent effects were evident in DCs from both Leishmania major-susceptible (BALB/c) and -resistant (C3H/HeN) murine strains. These data suggest that modification of DC phenotype and function by MAX likely affects crucial cellular components that determine the pathological response to infection with Leishmania.

Protection of susceptible BALB/c mice from challenge with Leishmania major by nucleoside hydrolase, a soluble exo-antigen of Leishmania

Leishmania major culture-derived, soluble, exogenous antigens have been shown to be a source of vaccine targets for the parasite. We have previously reported that L. major culture-derived, soluble, exogenous antigens can immunize BALB/c mice against challenge with L. major. However, the molecule(s) involved in this protection was not known. We describe the potential of one component of soluble exogenous antigens (recombinant nucleoside hydrolase) to vaccinate mice against challenge with L. major. We found that recombinant nucleoside hydrolase vaccinated BALB/c mice against a subsequent challenge with L. major. Protection was manifested by a significant decrease in lesion size (as much as a 30-fold reduction) and parasite burden (as much as a 71-fold reduction). Protection was achieved whether recombinant nucleoside hydrolase was administered to mice in the presence or absence of adjuvant (interleukin-12). Finally, protection was accompanied by an increase in interferon-gamma production but a decrease in interleukin-10 production by vaccinated animals in response to challenge with L. major.

Objective evaluation of skin prick test reactions using digital photography

BACKGROUND

The skin prick test has been used worldwide to determine IgE-mediated hypersensitivity. However, the most current method to record this reaction has problems with accuracy and precision.

OBJECTIVE

To demonstrate a new approach to measure the skin prick reaction and its kinetics with precision.

METHODS

The skin prick test was induced using histamine or Dermatophagoides pteronyssinus antigen in 80 volunteers aged 4 and 67 years who had different skin colors. Digital photographs were obtained at 0, 3, 5, 10, 15 and 20 min. The mean wheal and erythema area as well as the erythema intensity were determined using Adobe Photoshop software. The accuracy and precision of this approach were also evaluated.

RESULTS

The digital photographic analysis measured the wheal and erythema sizes independent of the antigen or skin color with precision. In addition, a new variable of this test, the skin erythema intensity, could be determined objectively using the chromaticity of reflected light.

CONCLUSIONS

Digital photographic analysis is a precise and objective method to evaluate the skin prick test reaction, which can be used independent of the patient's skin color in clinical or research settings.

Immunomodulatory effects of the Lutzomyia longipalpis salivary gland protein maxadilan on mouse macrophages

Infection with Leishmania major is enhanced when the sand fly Lutzomyia longipalpis salivary peptide maxadilan (MAX) is injected along with the parasite. Here we determined the effect that MAX has on the secretion of cytokines and nitric oxide (NO) and on parasite survival in macrophages (MPhis). The cytokines produced by MPhis can enhance a type 1 response, which will increase NO and the killing of intracellular pathogens such as L. major, or a type 2 response, leading to antibody production that is ineffective against intracellular pathogens such as L. major. A mouse macrophage cell line (RAW 264.7) was stimulated with various concentrations of MAX and lipopolysaccharide (LPS), and the supernatants were collected after 1, 2, and 3 days. Supernatants were assayed for interleukin-12p70 (IL-12p70), IL-10, IL-6, transforming growth factor beta (TGF-beta), NO, and tumor necrosis factor alpha (TNF-alpha). Our results indicate that the addition of MAX upregulates the cytokines associated with a type 2 response (IL-10, IL-6, and TGF-beta) but downregulates type 1 cytokines (IL-12p70 and TNF-alpha) and NO. MAX was also added to L. major-infected mouse peritoneal exudate cells (PECs), and the parasite load increased significantly. The enhanced parasite load correlated with decreased NO production by PECs that were stimulated with LPS and gamma interferon in the presence of MAX. The ability of MAX to foster a type 2 response, to enhance parasite survival, and to decrease NO argues that MAX may be crucial for the early survival of Leishmania in the vertebrate host, and therefore, MAX holds considerable promise as an antigenic component for a vaccine against Leishmania.

Cross-protection against Leishmania donovani but not L. Braziliensis caused by vaccination with L. Major soluble promastigote exogenous antigens in BALB/c mice

Vaccinating with soluble Leishmania major promastigote exogenous antigens (LmSEAgs) protects mice against challenge with L. major. To explore the potential of LmSEAgs to cross-protect against infection with other species of Leishmania, BALB/c mice were immunized with LmSEAgs prior to challenge with either L. donovani or L. braziliensis promastigotes. Such mice were protected against L. donovani but not L. braziliensis infection. Leishmania braziliensis-infected mice developed lesions that were not significantly different from those of controls and that contained 13-fold more parasites. In contrast, immunized mice infected with L. donovani were protected as illustrated by low splenic parasite loads (as much as 4,913-fold fewer parasites). This protection corresponded to significant increases in gamma interferon and low production of interleukin-4 (IL-4) IL-4 or IL-10, which suggested an enhanced type 1 response.

Effect of Lutzomyia longipalpis salivary gland extracts on leukocyte migration induced by Leishmania major

The mechanism by which the salivary gland lysate (SGL) of Lutzomyia longipalpis enables Leishmania infection remains under investigation. One possibility is that saliva promotes cellular recruitment leading to development of skin lesions. In this study, we investigated leukocyte recruitment induced by L. major, L. major + SGL, or SGL alone into the peritoneal cavity of BALB/c mice. The administration of L. major with or without SGL induced neutrophil migration six hours after infection. Interestingly, after seven days, the BALB/c mice still had eosinophils and mononuclear cells in their peritoneal cavities. Flow cytometric analysis showed an increase in the CD4(+) CD45RB(low) T cell subset (effector or memory cells) compared with the CD4(+) CD45RB(high) subset (naive cells). Moreover, the co-injection of L. major with SGL enhanced production of interleukin-10. These results suggest that SGL can facilitate Leishmania infection by modulating leukocyte recruitment and Th2 cytokine production at the inflammatory focus.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) reduces Leishmania major burdens in C57BL/6 mice

Acute exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) can suppress adaptive immunity. In this study, pre-exposure of Leishmania major-infected mice to TCDD caused a dose-dependent and unexpected decrease in parasite burdens on day 20 after infection. In contrast, TCDD-mediated lymphoid atrophy, suppressed antibody levels, and enhanced interleukin-2 production were observed as expected. These results suggest that TCDD may enhance resistance to L. major in the face of immune suppression.

Salivary gland extracts of Culicoides sonorensis inhibit murine lymphocyte proliferation and no production by macrophages

Culicoides biting midges serve as vectors of pathogens affecting humans and domestic animals. Culicoides sonorensis is a vector of several arboviruses in North American that cause substantial economic losses to the US livestock industry. Previous studies showed that C. sonorensis saliva, like the saliva of many hematophagous arthropods, contains numerous pharmacological agents that affect hemostasis and early events in the inflammatory response, which may enhance the infectivity of Culicoides-borne pathogens. This paper reports on the immunomodulatory properties of C. sonorensis salivary gland extracts on murine immune cells and discusses the possible immunomodulatory role of C. sonorensis saliva in vesicular stomatitis virus infection of vertebrate hosts. Splenocytes treated with C. sonorensis mitogens were significantly affected in their proliferative response, and peritoneal macrophages secreted significantly less NO. A 66-kDa glycoprotein was purified from C. sonorensis salivary gland extract, which may be in part responsible for these observations and may be considered as a vaccine candidate.

Is it possible to develop pan-arthropod vaccines?

Hematophagous arthropods that transmit the etiological agents of arthropod-borne diseases have become the focus of anti-vector vaccines, targeted mainly at components of their saliva and midgut. These efforts have been directed mostly towards developing species-specific vaccines. An alternative is to target cross-reactive epitopes that have been preserved during evolution of the arthropods. The N- and O-linked glycans that are attached to arthropod glycoproteins are one of the potential targets of this pan-arthropod vaccine approach. Here, we discuss how genetically modified Drosophila melanogaster cells can be used to synthesize and to deliver these arthropod glycans to vertebrate hosts.

The immunomodulatory factors of arthropod saliva and the potential for these factors to serve as vaccine targets to prevent pathogen transmission

In general, attempts to develop vaccines for pathogens transmitted by arthropods have met with little or no success. It has been widely observed that the saliva of arthropods that transmit disease enhances the infectivity of pathogens the arthropod transmits to the vertebrate host. Indeed, it has been observed that vaccinating against components of the saliva of arthropods or against antigens expressed in the gut of arthropods can protect the host from infection and decrease the viability of the arthropod. These results suggest that multi-subunit vaccines that target the pathogen itself as well as arthropod salivary gland components and arthropod gut antigens may be the most effective at controlling arthropod-borne pathogens as these vaccines would target several facets of the lifecycle of the pathogen. This review covers known immunomodulators in arthropod salivary glands, instances when arthropod saliva has been shown to enhance infection and a limited number of examples of antiarthropod vaccines, with emphasis on three arthropods: sandflies, mosquitoes and hard ticks.

Novel compounds active against Leishmania major

Leishmania major is an important trypanosomatid pathogen that causes leishmaniasis, which is a serious disease in much of the Old World. Current treatments include a small number of antimony compounds that, while somewhat effective, are limited by serious side effects. We have screened a small portion of a unique chemical library and have found at least three novel compounds that are effective against L. tarentolae and L. major in vitro and in a murine macrophage model of L. major infection. These compounds were effective in both assays at doses significantly lower than those of sodium stibogluconate (Pentostam) and represent possible candidates for drug development.

The role of vector saliva in transmission of arthropod-borne disease

Blood-sucking arthropod disease vectors all share one important feature: while probing for blood in the vertebrate host's skin they salivate into the wound they create. Recent studies on the pharmacological properties of vector saliva have revealed an array of activities that are potentially beneficial to both the vector and to the pathogen. These observations may help explain why certain vectors and pathogens have co-evolved. In this article, Richard Titus and Jose Ribeiro discuss the role vector saliva may play in disease transmission, and the prospects for its use in the control of arthropod-borne pathogens.

Characterization of the early cellular immune response to Leishmania major using peripheral blood mononuclear cells from Leishmania-naive humans

While the response to Leishmania major is well characterized in mice, there is much less known about the human immune response, particularly early after exposure to the parasite. Therefore, we developed a primary in vitro (PIV) system that allowed us to address these questions. We co-cultured peripheral blood mononuclear cells from Leishmania-naive donors with L. major parasites and found that the responding PIV cells produced interferon-gamma and interleukin-12 (IL-12). When restimulated, these PIV cells also occasionally produced IL-5. Both CD4 and CD8 cells and both HLA class I and II cell activation pathways appeared to play a role in the PIV system, and cell activation was dependent upon the presence of antigen-presenting cells. Moreover, PIV cells generated with L. major showed considerable cross-reactivity with other species of Leishmania. Finally, the PIV cells augmented intracellular killing of L. major when they were co-cultured with macrophages infected with the parasite.

Immunization with Leishmania major exogenous antigens protects susceptible BALB/c mice against challenge infection with L. major

The potential of Leishmania major culture-derived soluble exogenous antigens (SEAgs) to induce a protective response in susceptible BALB/c mice challenged with L. major promastigotes was investigated. Groups of BALB/c mice were immunized with L. major SEAgs alone, L. major SEAgs coadministered with either alum (aluminum hydroxide gel) or recombinant murine interleukin-12 (rmIL-12), L. major SEAgs coadministered with both alum and rmIL-12, and L. major SEAgs coadministered with Montanide ISA 720. Importantly and surprisingly, the greatest and most consistent protection against challenge with L. major was seen in mice immunized with L. major SEAgs alone, in the absence of any adjuvant. Mice immunized with L. major SEAgs had significantly smaller lesions that at times contained more than 100-fold fewer parasites. When lymphoid cells from L. major SEAg-immunized mice were stimulated with leishmanial antigen in vitro, they proliferated and secreted a mixed profile of type 1 and type 2 cytokines. Finally, analyses with Western blot analyses and antibodies against three surface-expressed and secreted molecules of L. major (lipophosphoglycan, gp46/M2/PSA-2, and gp63) revealed that two of these molecules are present in L. major SEAgs, lipophosphoglycan and the molecules that associate with it and gp46/M2/PSA-2.

Characterization of an I-E-restricted, gp63-specific, CD4-T-cell clone from Leishmania major-resistant C3H mice that secretes type 2 cytokines and exacerbates infection with L. major

A T-cell clone (designated KLmB-3) was derived from resistant C3H mice 2 weeks after infection with Leishmania major. KLmB-3 was a CD4-T-cell clone that utilized the V beta 8.1 T-cell receptor. When adoptively transferred to naive C3H mice, KLmB-3 unexpectedly exacerbated infection with L. major (it increased the cutaneous lesion size and the parasite burden within the lesion). The ability of KLmB-3 to exacerbate disease correlated with its ability to produce the type 2-associated cytokines interleukin-4 (IL-4), IL-5, IL-10, and transforming growth factor beta. Interestingly, KLmB-3 was specific for an epitope in the amino-terminal end of the L. major surface gp63 zinc metalloproteinase (leishmanolysin) that has been shown to be capable of inducing a protective immune response. Moreover, KLmB-3 was activated when this epitope was presented in the context of H-2 I-E rather than H-2 I-A.

THE HUMAN CYTOKINE RESPONSE TO LEISHMANIA MAJOR EARLY AFTER EXPOSURE TO THE PARASITE IN VITRO

Leishmaniasis is caused by the protozoan parasite Leishmania spp. In murine leishmaniasis, a T helper cell type-I (Th1) response, characterized by the secretion of interferon (IFN)-gamma is necessary for clearing the infection. whereas a Th2 response, accompanied by the production of interleukin (IL)-5, can exacerbate the disease. Moreover, the early cytokine milieu is thought to play an important role in determining the outcome of infection. In human leishmaniasis little is known about this early cytokine response. Because of this, we cocultured human peripheral blood mononuclear cells (PBMC) with Leishmania major in vitro and measured the production of IFN-gamma, IL-5, and IL-10. We also treated PBMC cultures with various cytokines and neutralizing anticytokines. We found that the principal cytokine produced was IFN-gamma and that its production was regulated by IL-10 and IL-12. In contrast, only low levels of Th2 cytokines such as IL-5 were produced. Therefore, the Th1-Th2 dichotomy that exists in inbred strains of mice does not appear to apply to the response of humans to L. major. Rather, Th2 cytokines may play a role in regulating IFN-gamma production.

Lutzomyia longipalpis salivary gland homogenate impairs cytokine production and costimulatory molecule expression on human monocytes and dendritic cells

In this report, we describe an investigation of the effects of Lutzomyia longipalpis sand fly salivary gland homogenates (SGH) on cytokine production and expression of costimulatory molecules on human monocytes, macrophages (Mphis), and dendritic cells (DCs). SGH of L. longipalpis induced an increase in interleukin-6 (IL-6), IL-8 and IL-12p40 production but a decrease in tumor necrosis factor alpha and IL-10 production by lipopolysaccharida (LPS)-stimulated monocytes. We also examined the expression of costimulatory molecules on the surface of monocytes, Mphis, and DCs. Whereas SGH affected the expression of these molecules on monocytes and Mphis, it had little effect on these molecules on DCs. However, when DCs were generated from human monocytes in the presence of SGH, SGH inhibited the expression of costimulatory molecules. In addition, a decrease in the maturation of DCs induced by CD40L was observed in the presence of SGH. Finally, preincubating SGH with human sera containing anti-SGH-specific antibodies abolished the effects of SGH on cytokine production by LPS-stimulated monocytes.

Short report: requirement of b cells for delayed type hypersensitivity-like pathology after secondary infection with Leishmania major in resistant C57BL/6 mice

B cell-deficient C57B1/6 (microMT) mice were resistant to Leishmania major after both primary and secondary parasite challenge. However, unlike in wild-type mice, secondary infection in microMT mice was not accompanied by a marked delayed type hypersensitivity-like response, and interferon-gamma (IFN-gamma) levels were approximately half of those in wild-type mice. These results suggest that B cells are involved in IFN-gamma production and the pathology of secondary infection.

Immunomodulatory effects of Maxadilan and Phlebotomus papatasi sand fly salivary gland lysates on human primary in vitro immune responses

Leishmaniasis is a parasitic disease transmitted by the bite of Leishmania-infected sand flies. Here we show for the first time the ability of Maxadilan (Max), a vasodilatory peptide isolated from the sand fly Lutzomyia longipalpis, and salivary gland lysate (SGL) from Phlebotomus papatasi to decrease the secretion of Type 1 cytokines and to enhance the production of the Type 2 cytokine interleukin (IL)-6 by human peripheral blood mononuclear cells (PBMC) and monocytes. We found Max decreased the secretion of interferon (IFN)-gamma and IL-12p40 by PBMC and TNF-alpha by monocytes. SGL reduced the production of IFN-gamma by PBMC. In contrast, production of the Type 2 cytokine IL-6 was increased in Max or SGL-exposed cells. Finally, we determined that Max interacts with human cells through at least the pituitary adenylate cyclase activating polypeptide receptor. These results show that sand fly salivary gland components have an immunomodulatory effect on human cells, and this has important implications for the development of vaccines against leishmaniasis for humans.

Infection with Leishmania major stimulates haematopoiesis in susceptible BALB/c mice and suppresses haematopoiesis in resistant CBA mice

Cytokine responses to Leishmania infection begin very early in infection, and differ between susceptible and resistant mice. Susceptibility to chronic Leishmania infection has been associated with increased haematopoiesis. To analyse the effect that acute infection with L. major has on bone-marrow haematopoiesis in susceptible (BALB/c) and resistant (CBA) mice, we enumerated erythroid progenitors and granulocyte-monocyte progenitors 3 days after infection. We found that haematopoiesis was stimulated in BALB/c mice infected with L. major, while haematopoiesis was inhibited in CBA mice. We found that this effect could be partially explained by cytokine production: interleukin-4 was involved in stimulation of BALB/c haematopoiesis and tumour necrosis factor-alpha was involved in inhibition of CBA haematopoiesis. Our conclusions are that haematopoietic changes occur shortly after L. major infection, and may be related to disease outcome.

Maxadilan, the vasodilator/immunomodulator from Lutzomyia longipalpis sand fly saliva, stimulates haematopoiesis in mice

Protozoal parasites of the genus Leishmania are transmitted to their vertebrate host within the saliva of the sand fly during a blood meal. The saliva of the sand fly Lutzomyia longipalpis contains maxadilan, a potent vasodilator and immunomodulator. Maxadilan has been shown to enhance the virulence of L. major in all strains of laboratory mice when injected along with the organism. Increased haematopoiesis has been associated with enhanced susceptibility to Leishmania organisms. Here, we show that maxadilan alone stimulates bone marrow haematopoiesis through its ability to stimulate interleukin-6 production by bone marrow stromal cells. Moreover, these effects of maxadilan are mediated through the interaction of maxadilan with the pituitary adenylate cyclase activating polypeptide receptor. These data suggest that increasing haematopoiesis may be yet another way that maxadilan enhances susceptibility of mice to Leishmania infection.

Type 1 and type 2 responses to Leishmania major

Leishmania major is a protozoan parasite that is transmitted to the mammalian host by its sand fly vector when the fly probes in the host's skin for a blood meal and injects the parasite within its saliva. In mice experimentally infected with L. major, outgrowth of CD4 type 1 (Th1) cells leads to resolution of the infection, but outgrowth of type 2 (Th2) cells exacerbates disease. To design an effective vaccine against the parasite (and other pathogens that induce polarized Th1 and Th2 responses), we must determine the mechanism underlying this phenomenon so that we can design the vaccine to elicit the appropriate (i.e., protective) Th cell. Recent work indicates that Th bias is influenced by a number of signals delivered by antigen-presenting cells, including cytokines and co-stimulatory molecules. Moreover, recent work also suggests that sand fly saliva influences the immune response to L. major and Th polarization. Determining the mechanisms that lead to polarized Th responses should expand our knowledge regarding immunity to L. major, and should add to our understanding of immunoregulation in general.

Sandfly maxadilan exacerbates infection with Leishmania major and vaccinating against it protects against L. major infection

Bloodfeeding arthropods transmit many of the world's most serious infectious diseases. Leishmania are transmitted to their mammalian hosts when an infected sandfly probes in the skin for a bloodmeal and injects the parasite mixed with its saliva. Arthropod saliva contains molecules that affect blood flow and modulate the immune response of the host. Indeed, sandfly saliva markedly enhances the infectivity of L. major for its host. If the salivary molecule(s) responsible for this phenomenon was identified, it might be possible to vaccinate the host against this molecule and thereby protect the host against infection with Leishmania. Such an approach represents a novel means of controlling arthropod-borne disease transmission. Here, we report that a single molecule, maxadilan, in sandfly saliva can exacerbate infection with L. major to the same degree as whole saliva, and that vaccinating against maxadilan protects mice against infection with L. major.

Interleukin-6 deficiency influences cytokine expression in susceptible BALB mice infected with Leishmania major but does not alter the outcome of disease

Since interleukin-6 (IL-6) may promote Th2 responses, we infected BALB IL-6-deficient (IL-6(-/-)) mice with Leishmania major. There was not a significant difference between the courses of infection (lesion size and parasite burden) in IL-6(-/-) and wild-type mice, but IL-6(-/-) mice expressed lower levels of Th2- and Th1-associated cytokines.

Leishmania major induces differential expression of costimulatory molecules on mouse epidermal cells

Levels of expression of costimulatory molecules have been proposed to influence the outcome of antigen-specific T cell priming. We found that Leishmania major selectively modulated the expression of costimulatory molecules on various populations of epidermal cells. B7.2 expression was down-regulated on Thy1.2+ epidermal cells (keratinocytes) from disease-resistant C3H mice, but not from disease-susceptible BALB/c mice. In addition, epidermal cells from BALB/c mice showed a down-regulation of B7.1 expression on NLDC 145+ Langerhans cells. In vitro T cell priming experiments, using syngeneic epidermal cells as antigen-presenting cells (APC), showed that the production of IFN-gamma was inhibited when either B7.1 or B7.2 signaling pathways were blocked. Blockade of B7.2, but not B7.1, significantly inhibited the ability of epidermal cells to induce IL-4 production from CD4+ T cells. In addition, C3H CD4+ T cells, which were unable to secrete detectable levels of IL-4 in cultures with syngeneic APC, were now able to secrete IL-4 following presentation of L. major antigens by congenic BALB/K epidermal cells. Conversely, C3H epidermal cells supported the priming of BALB/K CD4+ T cells for IL-4 production in vitro. Thus, the differential expression of B7 molecules on epidermal cells may not represent the sole factor governing the polarization of L. major-specific CD4+ T cells in vitro.

Regulation of differentiation to the infective stage of the protozoan parasite Leishmania major by tetrahydrobiopterin

A critical step in the infectious cycle of Leishmania is the differentiation of parasites within the sand fly vector to the highly infective metacyclic promastigote stage. Here, we establish tetrahydrobiopterin (H4B) levels as an important factor controlling the extent of metacyclogenesis. H4B levels decline substantially during normal development, and genetic or nutritional manipulations showed that low H4B caused elevated metacyclogenesis. Mutants lacking pteridine reductase 1 (PTR1) had low levels of H4B, remained infectious to mice, and induced larger cutaneous lesions (hypervirulence). Thus, the control of pteridine metabolism has relevance to the mechanism of Leishmania differentiation and the limitation of virulence during evolution.

Identification of an IL-2 binding protein in the saliva of the Lyme disease vector tick, Ixodes scapularis

A potent inhibitor of mitogen-stimulated T cell proliferation exists in the saliva of several species of hard ticks, including the Lyme disease vector tick, Ixodes scapularis. Our characterization of this phenomenon has led to the identification of a possible mechanism for the T cell inhibitory activity of I. scapularis saliva. The T cell inhibitor can overcome stimulation of mouse spleen cells with anti-CD3 mAb; however, a direct and avid interaction with T cells does not appear to be necessary. Tick saliva inhibits a mouse IL-2 capture ELISA, suggesting that a soluble IL-2 binding factor is present in the saliva. This hypothesis was verified by using a direct binding assay in which plate-immobilized tick saliva was shown to bind both mouse and human IL-2. Elimination of the IL-2 binding capacity of saliva in the in vitro assays by trypsin digestion demonstrated that the IL-2 binding factor is a protein. These experiments comprise the first demonstration of the existence of such a secreted IL-2 binding protein from any parasite or pathogen. This arthropod salivary IL-2 binding capacity provides a simple mechanism for the suppression of T cell proliferation as well as for the activity of other immune effector cells that are responsive to IL-2 stimulation. Relevance of the tick T cell inhibitory activity to the human immune system is demonstrated by the ability of tick saliva to inhibit proliferation of human T cells and CTLL-2 cells grown in the presence of human IL-2.

Major histocompatibility complex class II-independent generation of neutralizing antibodies against T-cell-dependent Borrelia burgdorferi antigens presented by dendritic cells: regulation by NK and gammadelta T cells

We previously showed that adoptive transfer of Borrelia burgdorferi-pulsed dendritic cells (DCs) into syngeneic mice protects animals from challenge with tick-transmitted spirochetes. Here, we demonstrate that the protective immune response is antibody (Ab) dependent and does not require the presence of major histocompatibility complex (MHC) class II molecules on DCs. Mice sensitized with B. burgdorferi-pulsed MHC class II-deficient (MHC class II(-/-)) DCs mounted a humoral response against protective antigens, including B. burgdorferi outer surface protein A (OspA) and OspC. B-cell help for the generation of neutralizing anti-OspC immunoglobulin G Abs could be provided by gammadelta T cells. In contrast, anti-OspA Ab production required the presence of alphabeta T cells, although this pathway could be independent of MHC class II molecules on antigen-presenting cells. Moreover, depletion of NK cells prior to transfer of antigen-pulsed MHC class II(-/-) DCs resulted in significant increases in the levels of neutralizing Abs induced by DCs. Altogether, these data suggest that the initial interactions between DCs and innate immune cells, such as gammadelta and NK cells, can influence the generation of a protective humoral response against B. burgdorferi antigens.

Influence of costimulatory molecules on immune response to Leishmania major by human cells in vitro

The importance of CD40, CD80, and CD86 costimulatory molecules in anti-Leishmania immune responses has been established in murine models. A role for these costimulatory molecules in human anti-Leishmania immune responses was investigated in this study. Autologous macrophages and peripheral blood leukocytes (PBL) were prepared from peripheral blood mononuclear cells of Leishmania-naive donors and cultured with or without Leishmania major in various combinations. After 7 days of culture, high levels of CD40 and CD86 were expressed on macrophages in the presence or absence of L. major. When macrophages were cultured for an additional 7 days with PBL, expression of all three costimulatory molecules was detected. When L. major was present in these cultures, the expression of CD80, and to a lesser extent CD40, on macrophages was enhanced. Blockade of CD80, CD86, or both molecules (in the order of greatest effect) in cultures containing macrophages, PBL, and L. major significantly inhibited the production of gamma interferon, interleukin-5 (IL-5), and IL-12. Blockade of CD40-CD154 interactions also significantly inhibited production of these cytokines in response to L. major. Production of IL-10 was unaltered by the blockade of these costimulatory molecules. Thus, these data suggest that CD40, CD80, and CD86 expression and regulation may significantly impact anti-Leishmania immune responses in humans.

The immunomodulatory factors of bloodfeeding arthropod saliva

There are potent immunomodulators in saliva of the bloodfeeding arthropods which transmit many of the world's most serious diseases that may benefit the arthropod by preventing the vertebrate host from becoming sensitized to the saliva. In addition, saliva can enhance transmission of parasites/pathogens by arthropods. As a result, vaccines that target the arthropod (e.g. salivary immunomodulators) should be considered as one component of multisubunit vaccines against arthropod-borne parasites/pathogens. Indeed, since vaccines against the pathogens themselves are often not fully protective, vaccines that target several facets of the life cycle of the pathogen may be the most effective at controlling disease transmission. This review covers known immunomodulatory factors in arthropod vector saliva, focusing mainly on sandflies and ixodid ticks.

Rapid early onset lymphocyte cell death in mice resistant, but not susceptible to Leishmania major infection

Leishmania major (Lm) infection in mice is a prototypical model for the role of immune deviation in disease resistance. Resistant strains of mice develop a Th1 response to Lm infection, distinguished by secretion of IL-12 and interferon gamma. In contrast, susceptible strains display sustained IL-4 expression characteristic of a Th2 response. However, when mechanisms of cell death are blocked, mice display a susceptible phenotype even in the presence of a strong Th1 response, suggesting that cell death, and not cytokine bias, may be an important factor in disease resistance. Here, we investigated this hypothesis by comparing lymphocyte cellularity, cell death and Fas expression in resistant CBA and susceptible BALB/c mice during the course of Lm infection. We found that delayed onset of cell death and late Fas induction correlated with massive lymphocyte accumulation and susceptibility to leishmaniasis, while early cell death and rapid Fas induction occurred in resistant mice.

Virulent or avirulent (dhfr-ts-) Leishmania major elicit predominantly a type-1 cytokine response by human cells in vitro

In this study we have compared the immune response of normal human cells cultured in vitro to two virulent strains of Leishmania major (CC1 and LV39), and to an avirulent vaccine strain (dhfr-ts-) made by targeted deletion of the essential gene DHFR-TS. We utilized an in vitro system in which naive T cells from normal human donors were primed with autologous Leishmania-infected macrophages. All three parasites infected macrophages and transformed into amastigotes within the cells. However, whereas LV39 and CC1 replicated in macrophages, dhfr-ts- did not. When peripheral blood lymphocytes (PBL) were stimulated with autologous macrophages infected with any of the three parasites, the lymphocytes produced a type-1-biased cytokine response. Finally, addition of IL-12 during the first stimulation period increased the production of interferon-gamma but decreased IL-5 secretion. On the other hand, anti-IL-12 resulted in the opposite effect.

Priming of a beta-galactosidase (beta-GAL)-specific type 1 response in BALB/c mice infected with beta-GAL-transfected Leishmania major

To determine whether an ongoing response to Leishmania major would affect the response to a non-cross-reacting, non-leishmanial antigen, susceptible BALB/c mice and resistant C3H mice were infected with L. major parasites expressing Escherichia coli beta-galactosidase (beta-GAL); this parasite was designated L. major-betaGAL. BALB/c and C3H mice responded to infection with L. major-betaGAL by mounting a CD4 T-cell response to both parasite antigens and to the reporter antigen, beta-GAL. The phenotypes of these T cells were characterized after generating T-cell lines from infected mice. As expected, BALB/c mice responded to infection with L. major-betaGAL by producing interleukin 4 in response to the parasite and C3H mice produced gamma interferon (IFN-gamma) in response to the parasite and beta-GAL. Interestingly, however, BALB/c mice produced IFN-gamma in response to beta-GAL. Taken together, these results demonstrate that priming of IFN-gamma-producing cells can occur in BALB/c mice despite the fact the animals are simultaneously mounting a potent Th2 response to L. major.

An OspC-specific monoclonal antibody passively protects mice from tick-transmitted infection by Borrelia burgdorferi B31

A murine monoclonal antibody directed against Borrelia burgdorferi B31 outer surface protein C (OspC) antigen was generated by a method whereby borreliae were inoculated into the mouse via the natural transmission mode of tick feeding. Passive immunization with this antibody resulted in protection of C3H/HeJ and outbred mice from a tick-transmitted challenge infection. Immunofluorescence staining of borrelia cells indicated surface exposure of the OspC epitope reactive with the monoclonal antibody.

A method for the isolation and analysis of leucocytic cells from Leishmanial ear lesions in mice

The standard model of experimental cutaneous leishmaniasis involves infection of mice with Leishmania major in a single footpad or the rump, and analysis of the subsequent immune response in draining lymph nodes. Relatively few studies have examined the lesion directly. Here, we describe a method for the isolation of cells from established leishmanial lesions in mouse ears. After physical disruption of lesion tissue and isolation of cells on density gradients, a variety of leucocytic cell phenotypes were identified by flow cytometry and cytology. The phenotypes of the viable cells obtained were similar, in proportion, to those observed in histologic sections of ear lesions. This technique may be useful for studying lesion-specific cell function within the first weeks after infection with Leishmania parasites.

Indomethacin treatment slows disease progression and enhances a Th1 response in susceptible BALB/c mice infected with Leishmania major

Prostaglandins of the E series inhibit the development of Th1 responses. When infected with Leishmania major, BALB/c mice fail to develop a Th1 response, but instead mount a Th2 response and die of the disease. Therefore, we treated L. major-infected BALB/c mice with indomethacin, which inhibits prostaglandin production. Indomethacin lessened disease severity (parasite burden and pathology), and promoted a Th1 response, but the mice still succumbed to infection. The explanation for these observations may be two-fold: (1) the beneficial effects of indomethacin were predominantly observed later in infection (beyond two weeks), a time at which indomethacin was unable to sufficiently block the development of a Th2 response; (2) indomethacin was unable to induce a Th1 response in BALB/c mice that was of the same magnitude as the Th1 response observed in C57BL/6 mice infected with L. major.

Variation in the salivary peptide, maxadilan, from species in the Lutzomyia longipalpis complex

Maxadilan is an approximately 7kDa peptide that occurs in the saliva of the sand fly Lutzomyia longipalpis. This peptide is a potent vasodilator and may also have immunomodulatory effects related to the pathogenesis of leishmanial infections. Variation in the primary DNA and inferred amino acid sequence of maxadilan is reported. Differences were found within and among natural field populations as well as among sibling species. Extensive amino acid sequence differentiation, up to 23%, was observed among maxadilan from different populations. This is a remarkable degree of polymorphism considering the small size of this peptide. The vasodilatory activity of maxadilan was equivalent among recombinant maxadilan variants. All maxadilan variants induce interleukin-6. Predicted secondary structure and hydrophobicity plots suggest that these characteristics are conserved among variant peptides. However, profiles based on the antigenic index do differ among peptides.

Resolution of an infection with Leishmania braziliensis confers complete protection to a subsequent challenge with Leishmania major in BALB/c mice

Both Leishmania major and L. braziliensis induce cutaneous leishmaniasis in BALB/c mice. Whereas BALB/c mice die of infection with L. major, they cure an infection with L. braziliensis. We report here that after curing an infection with L. braziliensis, BALB/c mice are resistant to challenge with L. major. When challenged with L. major, L. braziliensis pre-treated BALB/c mice mounted a delayed-type hypersensitivity response to L. major and produced high amounts of interferon-gamma (IFN-gamma) but low amounts of interleukin-4. The IFN-gamma produced by the L. braziliensis pre-infected mice was involved in the protection seen against L. major challenge since treating the mice with a neutralizing anti-IFN-gamma abrogated the protection. This suggests that cross-reactive antigen epitopes exist between L. braziliensis and L. major and that pre-infection with L. braziliensis primes BALB/c mice to epitopes on L. major that can elicit a protective Th1 response to the parasite.

Phlebotomus papatasi sand fly salivary gland lysate down-regulates a Th1, but up-regulates a Th2, response in mice infected with Leishmania major

A vertebrate host becomes infected with Leishmania major when the sand fly vector injects parasites into skin along with saliva. Previous studies showed that salivary gland lysate of the New World sand fly Lutzomyia longipalpis markedly enhanced L. major infection in CBA mice. However, L. major is an Old World parasite transmitted in nature by the Old World sand fly Phlebotomus papatasi. Here we examine the ability of P. papatasi salivary gland lysate to enhance infection (lesion size and parasite burden) by L. major. In addition, we examine the effects of salivary gland lysate on the immune response to L. major by monitoring the levels of cytokine mRNA from the lymph nodes draining cutaneous lesions. We found that P. papatasi salivary gland lysate dramatically exacerbated lesion development in disease-resistant CBA mice. This exacerbation of disease correlated with inhibition of the production of Thl cytokines and associated factors (IFN-gamma, IL-12, and inducible nitric oxide synthase), but with enhancement of the Th2 cytokine IL-4, whereas no changes in the levels of IL-10 and TGF-beta were noted. Importantly, salivary gland lysate directly up-regulated expression of IL-4 mRNA in mice in the absence of infection with L. major.

Phlebotomus papatasi Sand Fly Salivary Gland Lysate Down-Regulates a Th1, but Up-Regulates a Th2, Response in Mice Infected with Leishmania major

A vertebrate host becomes infected with Leishmania major when the sand fly vector injects parasites into skin along with saliva. Previous studies showed that salivary gland lysate of the New World sand fly Lutzomyia longipalpis markedly enhanced L. major infection in CBA mice. However, L. major is an Old World parasite transmitted in nature by the Old World sand fly Phlebotomus papatasi. Here we examine the ability of P. papatasi salivary gland lysate to enhance infection (lesion size and parasite burden) by L. major. In addition, we examine the effects of salivary gland lysate on the immune response to L. major by monitoring the levels of cytokine mRNA from the lymph nodes draining cutaneous lesions. We found that P. papatasi salivary gland lysate dramatically exacerbated lesion development in disease-resistant CBA mice. This exacerbation of disease correlated with inhibition of the production of Th1 cytokines and associated factors (IFN-γ, IL-12, and inducible nitric oxide synthase), but with enhancement of the Th2 cytokine IL-4, whereas no changes in the levels of IL-10 and TGF-β were noted. Importantly, salivary gland lysate directly up-regulated expression of IL-4 mRNA in mice in the absence of infection with L. major.

The PACAP-type I receptor agonist maxadilan from sand fly saliva protects mice against lethal endotoxemia by a mechanism partially dependent on IL-10

Sand fly saliva contains maxadilan, a peptide that causes vasodilation and modifies the secretion of pro-inflammatory cytokines by macrophages. We show that 1 to 10 microg maxadilan protected BALB/c mice against a lethal dose of LPS. Maxadilan reduced serum levels of TNF-alpha by approximately tenfold, while it caused a threefold increase in IL-6 and IL-10. The protective effect of maxadilan is partially dependent on its ability to induce IL-10 production since maxadilan did not prevent death from endotoxic shock in IL-10(-/-) mice. Finally, maxadilan is a selective agonist of the pituitary adenylate cyclase-activating peptide (PACAP) type I receptor, and we found that the natural ligand of this receptor (PACAP 38) also protected mice against lethal endotoxemia. These results indicate that activation of the PACAP type I receptor may contribute to the control of systemic inflammation by a mechanism that is partially dependent on IL-10.

The Vasoactive Peptide Maxadilan from Sand Fly Saliva Inhibits TNF-α and Induces IL-6 by Mouse Macrophages Through Interaction with the Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Receptor

Maxadilan is a vasodilatory peptide encoded by a gene cloned from Lutzomyia longipalpis salivary glands. In this study we investigated the effects of maxadilan on macrophage functions. Maxadilan treatment of LPS-stimulated BALB/c macrophages inhibited TNF-α release but increased IL-6. Further, it also induced IL-6 release in a dose-dependent manner from unstimulated macrophages. Maxadilan increased production of PGE2, and the inhibition of TNF-α was completely abrogated by indomethacin. Others have recently shown that maxadilan is a selective agonist of the pituitary adenylate cyclase-activating polypeptide (PACAP) type I receptor. Treatment with the receptor antagonist PACAP 6–38 blocked maxadilan activities on macrophages. The natural endogenous ligand, PACAP 38, had the same effects as maxadilan on TNF-α and IL-6 production. Finally, in a dose- and time-dependent fashion, maxadilan induced the intracellular accumulation of cAMP in macrophages. Taken together, the results presented here indicate a modulatory effect of ligands of PACAP type I receptor on cytokine production by macrophages and suggest that activation of this receptor, with the subsequent elevation of intracellular cAMP in macrophages, could participate in a negative-feedback mechanism that controls certain inflammatory responses.

The vasoactive peptide maxadilan from sand fly saliva inhibits TNF-alpha and induces IL-6 by mouse macrophages through interaction with the pituitary adenylate cyclase-activating polypeptide (PACAP) receptor

Maxadilan is a vasodilatory peptide encoded by a gene cloned from Lutzomyia longipalpis salivary glands. In this study we investigated the effects of maxadilan on macrophage functions. Maxadilan treatment of LPS-stimulated BALB/c macrophages inhibited TNF-alpha release but increased IL-6. Further, it also induced IL-6 release in a dose-dependent manner from unstimulated macrophages. Maxadilan increased production of PGE2, and the inhibition of TNF-alpha was completely abrogated by indomethacin. Others have recently shown that maxadilan is a selective agonist of the pituitary adenylate cyclase-activating polypeptide (PACAP) type I receptor. Treatment with the receptor antagonist PACAP 6-38 blocked maxadilan activities on macrophages. The natural endogenous ligand, PACAP 38, had the same effects as maxadilan on TNF-alpha and IL-6 production. Finally, in a dose- and time-dependent fashion, maxadilan induced the intracellular accumulation of cAMP in macrophages. Taken together, the results presented here indicate a modulatory effect of ligands of PACAP type I receptor on cytokine production by macrophages and suggest that activation of this receptor, with the subsequent elevation of intracellular cAMP in macrophages, could participate in a negative-feedback mechanism that controls certain inflammatory responses.

Analysis of the immune responses of mice to infection with Leishmania braziliensis

Leishmania major and Leishmania braziliensis both cause cutaneous leishmaniasis, but the former kills BALB/c mice while the latter is killed by the mice. This killing of L. braziliensis occurred by a gamma interferon-dependent mechanism, potentially made possible by the observed lack of high interleukin-4 production.

Histologic characterization of experimental cutaneous leishmaniasis in mice infected with Leishmania braziliensis in the presence or absence of sand fly vector salivary gland lysate

Leishmania braziliensis is the causative agent of human cutaneous leishmaniasis in parts of the New World. In the murine model of infection, L. braziliensis does not produce severe or lasting cutaneous lesions in either BALB/c or C3H mice. However, when the parasites are injected into BALB/c mice with salivary gland lysate of the sand fly vector for the parasite, infection is significantly enhanced, as measured by lesion size, parasite burden, and the outcome of infection. Histologic examination of these cutaneous lesions showed that initially, nodular and diffuse dermal infiltrates of neutrophils, eosinophils, and histiocytes occurred in all mice. Over time, the saliva-free lesions progressed to small organized granulomas of epithelioid macrophages that contained few parasites, with eventual resolution of inflammation and mild dermal fibrosis. The saliva-associated lesions progressed to extensive, poorly organized accumulations of heavily parasitized epithelioid macrophages, with persistent neutrophils and eosinophils, and minimal fibroplasia. These results indicate that sand fly salivary gland lysate markedly modifies the inflammatory response to infection with L. braziliensis.