The influence of the site of parasite inoculation on the development of Th1 and Th2 type immune responses in (BALB/c x C57BL/6) F1 mice infected with Leishmania major

A Mouse Model of Ulcerative Cutaneous Leishmaniasis by Leishmania (Viannia) panamensis to Investigate Infection, Pathogenesis, Immunity, and Therapeutics

A mouse model of cutaneous leishmaniasis (CL) by Leishmania (Viannia) panamensis (L(V)p) that reproduces the characteristics of the human disease remains elusive. Here we report the development of a CL model that uses a mouse-adapted L(V)p isolate to reproducibly induce a dermal disease with a remarkable similarity to human CL. BALB/c mice infected intradermally in the ear with 105 stationary UA-946 L(V)p promastigotes develop a progressive cutaneous disease that exhibits the typical ulcerated lesions with indurated borders observed in CL patients. Although most of parasites in the inoculum die within the first week of infection, the survivors vigorously multiply at the infection site during the following weeks, paralleling disease appearance and aggravation. Regional lymphadenopathy as well as lymphatic dissemination of parasites to draining lymph nodes (dLN) was evidenced early after infection. Viable parasites were also isolated from spleen at later timepoints indicating systemic parasitic dissemination, but, strikingly, no signs of systemic disease were observed. Increasing numbers of myeloid cells and T lymphocytes producing IFNγ and IL-4 were observed in the dLN as disease progressed. A mixed adaptive L(V)p-specific T cell-mediated response was induced, since ex vivo recall experiments using dLN cells and splenocytes revealed the production of type 1 (IFNγ, IL-2), type 2 (IL-4, IL-13), regulatory (IL-10), and inflammatory (GM-CSF, IL-3) cytokines. Humoral adaptive response was characterized by early production of IgG1- followed by IgG2a-type of L(V)p-specific antibodies. IFNγ/IL-4 and IgG2a/IgG1 ratios indicated that the initial non-protective Th2 response was redirected toward a protective Th1 response. In situ studies revealed a profuse recruitment of myeloid cells and of IFNγ- and IL-4-producing T lymphocytes to the site of infection, and the typical histopathological changes induced by dermotropic Leishmania species. Evidence that this model is suitable to investigate pharmacological and immunomodulatory interventions, as well as for antigen discovery and vaccine development, is also presented. Altogether, these results support the validity and utility of this novel mouse model to study the pathogenesis, immunity, and therapeutics of L(V)p infections.

Immunological role of keratinocytes in leishmaniasis

Following inoculation of Leishmania, a protozoan parasite, into the skin of a mammal, the epidermal keratinocytes recognize the parasite and influence the local immune response that can give rise to different outcomes of leishmaniasis. The early keratinocyte-derived cytokines and keratinocytes-T cells interactions shape the anti-leishmanial immune responses that contribute to the resistance or susceptibility to leishmaniasis. The keratinocyte-derived cytokines can directly potentiate the leishmanicidal activity of monocytes and macrophages. As keratinocytes express MHC-II and enhance the expression of costimulatory molecules, these cells act as antigen-presenting cells (APCs) in cutaneous leishmaniasis (CL). Depending on the epidermal microenvironment, the keratinocytes induce various types of effector CD4⁺ T cells. Keratinocyte apoptosis and necrosis have been also implicated in ulceration in CL. Further, keratinocytes contribute to the healing of Leishmania-related cutaneous wounds. However, keratinocyte-derived IL-10 may play a key role in the development of post-kala-azar dermal leishmaniasis (PKDL). In this review, a comprehensive discussion regarding the multiple roles played by keratinocytes during leishmaniasis was provided, while highlighting novel insights concerning the immunological and pathological roles of these cells.

Experimental Cutaneous Leishmaniasis: Mouse Models for Resolution of Inflammation Versus Chronicity of Disease

Experimental cutaneous leishmaniasis of mice is a valuable model to study the immune response to the protozoan pathogen Leishmania and to define mechanisms of parasite control and resolution of inflammation as well as of parasite evasion and chronicity of disease. In addition, over many years Leishmania-infected mice have been successfully used to analyze the function of newly discovered immune cell types, transcription factors, cytokines, and effector mechanisms in vivo. In this chapter we present detailed protocols for the culture, propagation, and inoculation of Leishmania promastigotes, the monitoring of the course of cutaneous infection, the determination of the tissue parasite burden and for the phenotyping of the ensuing immune response. The focus lies on the L. major mouse model, but an overview on other established models of murine cutaneous leishmaniasis is also provided.

The skin immune atlas: three-dimensional analysis of cutaneous leukocyte subsets by multiphoton microscopy

Site-specific differences in skin response to pathogens and in the course of cutaneous inflammatory diseases are well appreciated. The composition and localization of cutaneous leukocytes has been studied extensively using histology and flow cytometry. However, the precise three-dimensional (3D) distribution of distinct immune cell subsets within skin at different body sites requires visualization of intact living skin. We used intravital multiphoton microscopy in transgenic reporter mice in combination with quantitative flow cytometry to generate a 3D immune cell atlas of mouse skin. The 3D location of innate and adaptive immune cells and site-specific differences in the densities of macrophages, T cells and mast cells at four defined sites (ear, back, footpad, tail) is presented. The combinatorial approach further demonstrates an as yet unreported age-dependent expansion of dermal gamma-delta T cells. Localization of dermal immune cells relative to anatomical structures was also determined. While dendritic cells were dispersed homogeneously within the dermis, mast cells preferentially localized to the perivascular space. Finally, we show the functional relevance of site-specific mast cell disparities using the passive cutaneous anaphylaxis model. These approaches are applicable to assessing immune cell variations and potential functional consequences in the setting of infection as well as the pathogenesis of inflammatory skin conditions.

Site-dependent recruitment of inflammatory cells determines the effective dose of Leishmania major

The route of pathogen inoculation by needle has been shown to influence the outcome of infection. Employing needle inoculation of the obligately intracellular parasite Leishmania major, which is transmitted in nature following intradermal (i.d.) deposition of parasites by the bite of an infected sand fly, we identified differences in the preexisting and acute cellular responses in mice following i.d. inoculation of the ear, subcutaneous (s.c.) inoculation of the footpad, or inoculation of the peritoneal cavity (intraperitoneal [i.p.] inoculation). Initiation of infection at different sites was associated with different phagocytic populations. Neutrophils were the dominant infected cells following i.d., but not s.c. or i.p., inoculation. Inoculation of the ear dermis resulted in higher frequencies of total and infected neutrophils than inoculation of the footpad, and these higher frequencies were associated with a 10-fold increase in early parasite loads. Following inoculation of the ear in the absence of neutrophils, parasite phagocytosis by other cell types did not increase, and fewer parasites were able to establish infection. The frequency of infected neutrophils within the total infected CD11b(+) population was higher than the frequency of total neutrophils within the total CD11b(+) population, demonstrating that neutrophils are overrepresented as a proportion of infected cells. Employing i.d. inoculation to model sand fly transmission of parasites has significant consequences for infection outcome relative to that of s.c. or i.p. inoculation, including the phenotype of infected cells and the number of parasites that establish infection. Vector-borne infections initiated in the dermis likely involve adaptations to this unique microenvironment. Bypassing or altering this initial step has significant consequences for infection.

The absence of B lymphocytes reduces the number and function of T-regulatory cells and enhances the anti-tumor response in a murine tumor model

Increasing evidence suggests that B lymphocytes play a central role in inhibiting the immune response against certain tumors, but the underlying mechanisms by which B cells facilitate tumor growth are still poorly understood. In this study, we investigated how the presence or absence of B cells affects expansion and function of T-regulatory cells ('T-regs') in a murine breast tumor model (EMT-6). We compared tumor growth, and the number and function of T-reg cells in wild-type immune-competent mice (ICM) and B-cell-deficient mice (BCDM). Mice were either tumor-naive or implanted with EMT-6 mammary adenocarcinoma cells. Tumor growth was markedly inhibited in BCDM, compared to wild-type mice (ICM). Increased T-reg expansion as defined by CD4+/CD25+/FOXP3+ cells was evident following EMT-6 inoculation in ICM in comparison with non-tumor-bearing mice or compared to BCDM in which tumor had been implanted. The percentage and absolute number of T-regs in the spleen, tumor draining lymph nodes, and tumor bed were significantly reduced in BCDM compared to ICM. T-reg function, measured by suppression and proliferation assays, was also reduced in tumor inoculated BCDM compared to ICM. Our studies indicate that absence of B cells may play a role in augmenting the T-cell anti-tumor response, in part due to effects on T-regulatory cell expansion and function.

Kinetic analysis of ex vivo human blood infection by Leishmania

The leishmanioses, vector-borne diseases caused by the trypanosomatid protozoan Leishmania, are transmitted to susceptible mammals by infected phlebotomine sand flies that inoculate promastigotes into hemorrhagic pools created in host skin. We assumed that promastigotes are delivered to a blood pool, and analyzed early promastigote interactions (0-5 min) with host components, which lead to parasite endocytosis by blood leukocytes, and to host infection. Promastigotes were incubated with NHS or with heparinized blood in near-physiological conditions, and we used cell radioimmunoassay and flow cytometry to measure the on-rate constants (k(+1)) of promastigote interactions with natural opsonins and erythrocytes. We obtained quantitative data for parasitized cells to determine the time-course of promastigote binding and internalization by blood leukocytes. In these reactions, promastigotes bind natural opsonins, immune adhere to erythrocytes and activate complement cytolysis, which kills approximately 95% of promastigotes by 2 min post-infection. C3-promastigote binding is a key step in opsonization; nascent C3-promastigotes are the substrate for two simultaneous reactions, C3-promastigote immune adherence (IA) to erythrocytes and complement-mediated promastigote killing. The k(+1) for IA was 75-fold greater than that for promastigote killing, showing that IA facilitates promastigote endocytosis and circumvents lysis. At 5 min post-infection, when reaction velocity is still linear and promastigote concentration is not limiting, 17.4% of granulocytes and 10.7% of monocytes had bound promastigotes, of which approximately 50% and approximately 25%, respectively, carried surface-bound (live) or internalized (live and dead) leishmanias. Of other leukocyte types, 8.5% of B cells bound but did not internalize promastigotes, and T cells, NK cells and CD209(+) dendritic cells did not bind parasites. These data show that, once in contact with blood, promastigote invasion of human leukocytes is an extremely rapid and efficient reaction, and suggest that the IA reaction constitutes a central strategy for this parasite in subverting host innate immune defenses.

Keratinocytes determine Th1 immunity during early experimental leishmaniasis

Experimental leishmaniasis is an excellent model system for analyzing Th1/Th2 differentiation. Resistance to Leishmania (L.) major depends on the development of a L. major specific Th1 response, while Th2 differentiation results in susceptibility. There is growing evidence that the microenvironment of the early affected tissue delivers the initial triggers for Th-cell differentiation. To analyze this we studied differential gene expression in infected skin of resistant and susceptible mice 16h after parasite inoculation. Employing microarray technology, bioinformatics, laser-microdissection and in-situ-hybridization we found that the epidermis was the major source of immunomodulatory mediators. This epidermal gene induction was significantly stronger in resistant mice especially for several genes known to promote Th1 differentiation (IL-12, IL-1β, osteopontin, IL-4) and for IL-6. Expression of these cytokines was temporally restricted to the crucial time of Th1/2 differentiation. Moreover, we revealed a stronger epidermal up-regulation of IL-6 in the epidermis of resistant mice. Accordingly, early local neutralization of IL-4 in resistant mice resulted in a Th2 switch and mice with a selective IL-6 deficiency in non-hematopoietic cells showed a Th2 switch and dramatic deterioration of disease. Thus, our data indicate for the first time that epidermal cytokine expression is a decisive factor in the generation of protective Th1 immunity and contributes to the outcome of infection with this important human pathogen.

To clear skin infections with the parasite Leishmania major, a specific T-helper (Th)-cell immune response has to be generated. The type of Th-cell response is determined early after infection by yet unknown mechanisms. In resistant mice a Th1-pattern is generated. A Th2-pattern in BALB/c mice, however, results in susceptibility. An analysis of these mechanisms is important for a better understanding of both host-parasite interactions and non-infectious Th-cell driven inflammatory skin disorders (e.g. atopic dermatitis). We analyzed how the infected skin influenced the Th-cell response. Therefore, we compared gene-expression early after infection in the skin of resistant and susceptible mice. Several cytokines (like IL-1β, IL-12, osteopontin, IL-4 and IL-6) were more strongly produced in the skin of resistant mice and therefore could be important for Th1-differentiation. We demonstrated that they were expressed by epidermal keratinocytes. Using mice with a deficiency for IL-6 in keratinocytes but not in immune cells and by inhibiting the action of early produced IL-4 we revealed that keratinocyte-derived IL-6 and IL-4 are important for resistance against Leishmania. Thus, our results indicate that the epidermis controls Th1-differentiation and may be a new pharmacological target for modification of Th-differentiation.

Evaluation of T cell responses in healing and nonhealing leishmaniasis reveals differences in T helper cell polarization ex vivo and in vitro

Experimental leishmaniasis is widely used to study the effector functions of T helper cell subsets in vivo. Healing and nonhealing Leishmania major infections have been correlated with T helper 1 and T helper 2 responses, respectively. In the present study, we determined T cell effector functions ex vivo, without any further restimulation and compared them to those obtained following antigen-specific restimulation in vitro. Our results show that T helper cell responses are significantly less polarized when determined ex vivo as compared to those measured after restimulation in vitro. Moreover, the differences in CD4⁺ T cell proliferation observed between healer and nonhealer strains of mice differed ex vivo and in vitro. Our results suggest that determination of both ex vivo as well as in vitro T cell responses is crucial to characterize immune responses during experimental leishmaniasis.

Leishmania major intracellular survival is not altered in SHP-1 deficient mev or CD45-/- mice

Protozoan parasites of the genus Leishmania escape from the immune response by interfering with signal transduction pathways of its host cell, the macrophage, thereby establishing permissive conditions for intracellular survival. Inhibition of macrophage activation after Leishmania infection has been suggested to require activation of the host cell phosphatase SHP-1. However, by utilizing infections of SHP-1 deficient (me(v)) and CD45 null mutant mice or macrophages, we provide evidence that intracellular survival of Leishmania major is not generally dependent on these cellular phosphatases.

The absence of cutaneous lymph nodes results in a Th2 response and increased susceptibility to Leishmania major infection in mice

Lymph nodes (LNs) are important sentinel organs where antigen-presenting cells interact with T cells to induce adaptive immune responses. In cutaneous infection of mice with Leishmania major, resistance depends on the induction of a T-helper-cell-1 (Th1)-mediated cellular immune response in draining, peripheral LNs. We investigated whether draining, peripheral LNs are absolutely required for resistance against L. major infection. We investigated the course of experimental leishmaniasis in wild-type (wt) mice lacking peripheral LNs (pLNs), which we generated by in utero blockade of membrane-bound lymphotoxin, and in mice lacking pLNs or all LNs due to genetic deletion of lymphotoxin ligands or receptors. wt mice of the resistant C57BL/6 strain without local skin-draining LNs were still able to generate specific T-cell responses, but this yielded Th2 cells. This switch to a Th2 response resulted in severe systemic infection. We also confirmed these results with mice lacking pLNs due to genetic depletion of lymphotoxin-beta. The complete absence of LNs due to a genetic depletion of the lymphotoxin-beta receptor also resulted in a marked deterioration of disease and a Th2 response. Thus, in the absence of pLNs, an L. major-specific Th2 response is induced in the remaining secondary lymphoid organs, such as the spleen and non-skin-draining LNs. This indicates a critical requirement for pLNs to induce protective Th1 immunity and suggests that whether Th1 or Th2 priming to the same antigen occurs depends on the site of the primary antigen recognition.

Genetic background influences immune responses and disease outcome of cutaneous L. mexicana infection in mice

The experimental model of high-dose Leishmania mexicana infection is used frequently to study molecular mechanisms regulating Th2 response since most inbred mice regardless of their genetic background display Th2 cytokine-dependent susceptibility to L. mexicana unlike Leishmania major. Here, we analyzed the course of L. mexicana infection in BALB/c, C57BL/6 and CBA/J mouse strains using low-dose ear infection model that mimics natural transmission. Although all three strains were equally susceptible to high-dose back rump L. mexicana infection, they displayed marked differences in their ability to control parasite growth after low-dose ear infection. Leishmania mexicana-infected BALB/c mice produced high levels of Th2-associated cytokines and developed non-healing lesions full of parasites, whereas CBA/J mice preferentially produced Th1-associated IFN-gamma but low levels of IL-4, and developed small self-resolving lesions. Both BALB/c and C57BL/6 mice produced comparable amounts of IFN-gamma following L. mexicana infection, but later produced less Th2-associated cytokines, and exhibited an 'intermediate' susceptibility phenotype characterized by lesion sizes that were significantly smaller than BALB/c mice but larger than CBA/J mice. Interestingly, all three strains also showed marked differences in trafficking of macrophages, CD4+ T cells and CD8+ T cells into their lesions. Finally, we analyzed the course of low-dose L. mexicana infection in signal transducers and activators of transcription (STAT) 6-/- and STAT6+/+ BALB/c mice. We found that STAT6-/- mice mount a Th1 response, produce high levels of IL-12 and IFN-gamma and develop smaller lesions containing fewer parasites as compared with STAT6+/+ mice. Our findings demonstrate that genetic background plays a critical role in determining susceptibility of inbred mice to low-dose L. mexicana infection. Furthermore, together with our previous findings, they show that STAT6-mediated signaling is involved in mediating susceptibility to L. mexicana following both high-dose back rump and low-dose ear dermis infection.

Conditions influencing the efficacy of vaccination with live organisms against Leishmania major infection

Numerous experimental vaccines have been developed with the goal of generating long-term cell-mediated immunity to the obligate intracellular parasite Leishmania major, yet inoculation with live, wild-type L. major remains the only successful vaccine in humans. We examined the expression of immunity at the site of secondary, low-dose challenge in the ear dermis to determine the kinetics of parasite clearance and the early events associated with the protection conferred by vaccination with live L. major organisms in C57BL/6 mice. Particular attention was given to the route of vaccination. We observed that the rapidity, strength, and durability of the memory response following subcutaneous vaccination with live parasites in the footpad are even greater than previously appreciated. Antigen-specific gamma interferon (IFN-gamma)-producing T cells infiltrate the secondary site by 1.5 weeks, and viable parasites are cleared as early as 2.5 weeks following rechallenge, followed by a rapid drop in IFN-gamma(+) CD4(+) cell numbers in the site. In comparison, intradermal vaccination with live parasites in the ear generates immunity that is delayed in effector cell recruitment to the rechallenge site and in the clearance of parasites from the site. This compromised immunity was associated with a rapid recruitment of interleukin-10 (IL-10)-producing CD4(+) T cells to the rechallenge site. Treatment with anti-IL-10-receptor or anti-CD25 antibody enhanced early parasite clearance in ear-vaccinated mice, indicating that chronic infection in the skin generates a population of regulatory cells capable of influencing the level of resistance to reinfection. A delicate balance of effector and regulatory T cells may be required to optimize the potency and durability of vaccines against Leishmaniasis and other intracellular pathogens.

Control of infection with Leishmania major in susceptible BALB/c mice lacking the common gamma-chain for FcR is associated with reduced production of IL-10 and TGF-beta by parasitized cells

Previous studies have shown that the in vitro ligation of FcgammaRs with IgG-opsonized Leishmania amastigotes promotes IL-10 production by macrophages. In addition, infection of either BALB/c mice lacking the common gamma-chain of Fc receptors (FcgammaR(-/-)) or mice genetically altered to lack circulating Ab (J(H)D) with Leishmania pifanoi results in reduced and delayed lesion development and a deficit in the recruitment of inflammatory cells into infected lesions. We show in this study that FcgammaR(-/-) mice can control infection with Leishmania major and totally resolve cutaneous lesions. The ability to eventually control infection is not associated with a reduction in lesion inflammation or a reduction in the ability of Leishmania to parasitize cells through week 6 of infection. The immune response in healing FcgammaR(-/-) mice is associated with a reduction in numbers of cells producing Th2-type cytokines, including IL-4 and IL-10, but not an increase in numbers of IFN-gamma-producing cells characteristic of a dominant Th1-type response. Instead, we observe a reduction in levels of IL-10 and TGF-beta within infected lesions, including reduced levels of these cytokines within parasitized macrophages. Together, these results suggest that uptake of opsonized parasites via FcgammaRs may be a strong in vivo stimulus for the production of anti-inflammatory cytokines that play a role in susceptibility to infection.

Protective immunogenicity of the paraflagellar rod protein 2 of Leishmania mexicana

Paraflagellar rod proteins (PFR) are a potent immunogen against experimental Trypanosoma cruzi infection. PFR are highly conserved among kinetoplastid parasites. We therefore evaluated the immunogenicity of the Leishmania mexicana pfr-2 gene and protein product in the hamster model of American cutaneous leishmaniasis. Immunization with pfr-2 DNA-induced specific antibody, confirming immunogenicity. Subsequent challenge with 10,000 and 500 stationary phase L. mexicana promastigotes respectively, resulted in delayed appearance of lesions, and significant reduction in lesions post infection in male hamsters, yet exacerbated lesions in female hamsters. Immunization with recombinant PFR-2 protein (rPFR-2) prevented lesion development in female hamsters challenged with L. panamensis, but was ineffective against L. mexicana. Nevertheless, prime boost immunization of female hamsters with rPFR and pfr-2 DNA significantly reduced lesion size following challenge with 500 L. mexicana promastigotes, supporting the relevance of PFR-2 as a potential vaccine constituent.

Re-examination of the immunosuppressive mechanisms mediating non-cure of Leishmania infection in mice

The interleukin (IL)-4 driven, polarized T-helper 2 cell (Th2) response that controls non-healing infection with Leishmania major in BALB/c mice has long been embraced as the underlying principle with which to consider the pathogenesis of non-healing and systemic forms of leishmaniasis in humans. The inability, however, to reveal a Th2 polarity associated with non-curing clinical disease has suggested that alternative cells and cytokines are involved in susceptibility. In this review, various mouse models of non-curing infection with L. major and other Leishmania species are re-examined in the context of the suppression mediated by IL-10 and regulatory T (Treg) cells. These activities are revealed in L. major-infected BALB/c IL-4 knockout (KO) and IL-4Ralpha KO mice and especially in non-cure resistant mice that do not default to a Th2 pathway as a result of inherent defects in Th1 differentiation. In contrast to the extreme BALB/c susceptibility arising from an aberrant Th2 response, non-cure in resistant mice arises from an imbalance in Treg cells that are activated in the context of an ongoing Th1 response and whose primary function may be to suppress the immunopathology associated with persistent antiparasite responses in infected tissues.

A coordinated cytotoxic effect of IFN-gamma and cross-reactive antibodies in the pathogenesis of Helicobacter pylori gastritis

BACKGROUND

Helicobacter pylori (H. pylori) infection is associated with chronic infiltration into the stomach by T cells and plasma cells producing IFN-gamma and antibodies of various specificities, respectively. It is unknown whether these lymphocyte-products may play coordinated roles in the gastric pathology of this infection.

AIMS

To know how IFN-gamma may relate to anti-H. pylori antibodies in their roles in pathogenesis, we determined the isotype subclass of those antibodies as well as their cross-reactivity and cytotoxicity to gastric epithelium.

METHODS AND RESULTS

We infected BALB/c mice with H. pylori (SS1, Sydney Strain 1) and generated monoclonal antibodies, which were comprised of 240 independent clones secreting immunoglobulin and included 80 clones reactive to SS1. Ninety percent of the SS1-reactive clones had IgG2a isotype. Two clones, 2B10 and 1A9, were cross reactive to cell surface antigens in H. pylori and to antigens of 28 KDa and 42 KDa, respectively, which were present on the cell surface of and shared by both mouse and human gastric epithelial cells. The antigens recognized by these monoclonal antibodies localized a distinctive area in the gastric glands. In the presence of complement, 2B10 showed cytotoxicity to gastric epithelial cells. The effect was dose dependant and augmented by IFN-gamma. Finally, administration of 2B10 to mice with SS1 infection aggravated gastritis by increasing cellular infiltration.

CONCLUSION

IFN-gamma by gastric T cells may participate in pathogenesis of the H. pylori infected stomach by directing an isotype-switch of anti-H. pylori antibodies to complement-binding subclass and by augmenting cytotoxic activity of a certain autoantibody. This may explain a host-dependent diversity in gastric pathology of the patients with H. pylori infection.

The site of cutaneous infection influences the immunological response and clinical outcome of hamsters infected with Leishmania panamensis

We determined that the site of inoculation (foot or snout) influences the clinical evolution and immune responses of hamsters infected with Leishmania (Viannia) panamensis. Hamsters infected in the snout showed (i) a more rapid and severe lesion evolution at multiple time points (P < 0.05), (ii) a more extensive inflammatory infiltrate and tissue necrosis, (iii) a higher tissue parasite burden, (iv) a higher antibody titre (P < 0.01), but lower antigen-specific spleen cell proliferative response (P = 0.02), and (v) a slower response to anti-leishmanial drug treatment (P < 0.002). In both inoculation groups there was co-expression of type 1 (IFN-gamma and IL-12) and some type 2 (IL-10 and TGF-beta, but not IL-4) cytokines in the cutaneous lesions and spleen. Early in the course of infection, hamsters infected in the snout showed higher expression of splenic IL-10 (P = 0.04) and intra-lesional IFN-gamma (P = 0.02) than foot infections. No expression of IL-12p40 or IL-4 was detected. During the chronic phase, snout lesions expressed more IFN-gamma (P = 0.001), IL-12p40 (P = 0.01), IL-10 (P = 0.009) and TGF-beta (P = 0.001), and the level of expression of each of these cytokines correlated with lesion size (P < or = 0.01). These results suggest that the site of infection influences the clinical outcome in experimental cutaneous leishmaniasis, and that the expression of macrophage-deactivating type 2 cytokines and/or an exaggerated type 1 proinflammatory cytokine response may contribute to lesion severity.

The immunology of susceptibility and resistance to Leishmania major in mice

Established models of T-helper-2-cell dominance in BALB/c mice infected with Leishmania major -- involving the early production of interleukin-4 by a small subset of Leishmania-specific CD4+ T cells -- have been refined by accumulating evidence that this response is not sufficient and, under some circumstances, not required to promote susceptibility. In addition, more recent studies in L. major-resistant mice have revealed complexities in the mechanisms responsible for acquired immunity, which necessitate the redesign of vaccines against Leishmania and other pathogens that require sustained cell-mediated immune responses.

Immunization of BALB/c mice with killed Neospora caninum tachyzoite antigen induces a type 2 immune response and exacerbates encephalitis and neurological disease

BALB/c mice were immunized subcutaneously with soluble Neospora caninum tachyzoite antigen (NSO) entrapped in nonionic surfactant vesicles (NISVs) or administered with Freund's complete adjuvant (FCA). Following virulent parasite challenge, groups of mice immunized with NSO and either NISVs or FCA had clinical neurological disease and increased numbers of brain lesions compared to groups of mice inoculated with FCA, NISVs, or phosphate-buffered saline (PBS) alone. Increased numbers of brain lesions were statistically significant only between mice immunized with NISV-NSO and NISV- or PBS-treated mice. Following parasite challenge, brain inflammatory infiltrates in all experimental and control groups of mice were relatively similar and consisted of compact infiltrates of macrophages admixed with various numbers of lymphoid cells. Increased brain lesions in NSO-immunized mice were associated with increased antigen-specific interleukin 4 (IL-4) secretion and increased IL-4:gamma interferon secretion ratios from splenocytes in vitro and increased antigen-specific immunoglobulin G1 (IgG1):IgG2a ratios in vivo. Thus, immunization with whole killed N. caninum antigen and either liposoidal or Freund's adjuvant induced a type 2 immune response that was associated with worsened disease. The present studies emphasize the need to identify specific N. caninum antigens or other delivery systems that will elicit protective immune responses to neosporosis.

Feedback mechanisms between T helper cells and macrophages in the determination of the immune response

The interactions between macrophages and T helper (Th) cells are a complex interplay of positive and negative signals. Some of the mathematical models of interactions between T helpers have indeed taken the influence of macrophages into account. In this work the macrophage is not considered as an extrinsic agent, that is duly directed by the T cells to be cytotoxic, nor is there consideration of T helper cell populations that are dominantly regulated by extrinsic properties of antigens per se, or by certain classes of presenting cells that preferentially select certain classes of lymphocytes or bias their commitment. Rather, a simplified model of feedback loops between Th cells and macrophages is formulated and analyzed. It is suggested how the mutual influence between Th and macrophages can determine the cytokine secretion pattern of these populations. The model provides a feedback scenario to account for experimental findings concerning reversal in the dominance of a specific cytokine profile in the course of some infections. A possible scenario accounting for the difference between the stability of Th1 and Th2 cytokine pattern is put forward. The model suggests explanations for the variability in the outcome of the immune response according to different body compartments. A rationale is presented that accounts for paradoxical findings indicating that Th1 cytokines are sometimes responsible for the downregulation of a Th1 dominated response.

Influence of microbiota in experimental cutaneous leishmaniasis in Swiss mice

Infection of Swiss/NIH mice with Leishmania major was compared with infection in isogenic resistant C57BL/6 and susceptible BALB/c mice. Swiss/NIH mice showed self-controlled lesions in the injected foot pad. The production of high levels of interferon-gamma (IFN-gamma) and low levels of interleukin-4 (IL-4) by cells from these animals suggests that they mount a Th1-type immune response. The importance of the indigenous microbiota on the development of murine leishmaniasis was investigated by infecting germfree Swiss/NIH in the hind footpad with L. major and conventionalizing after 3 weeks of infection. Lesions from conventionalized Swiss/NIH mice were significantly larger than conventional mice. Histopathological analysis of lesions from conventionalized animals showed abscesses of variable shapes and sizes and high numbers of parasitized macrophages. In the lesions from conventional mice, besides the absence of abscess formation, parasites were rarely observed. On the other hand, cells from conventional and conventionalized mice produced similar Th1-type response characterized by high levels of IFN-gamma and low levels of IL-4. In this study, we demonstrated that Swiss/NIH mice are resistant to L. major infection and that the absence of the normal microbiota at the beginning of infection significantly influenced the lesion size and the inflammatory response at the site of infection.

Anti-TGF-β Treatment Promotes Rapid Healing of Leishmania major Infection in Mice by Enhancing In Vivo Nitric Oxide Production

CB6F1 mice display intermediate susceptibility to Leishmania major infection compared with the highly susceptible BALB/c and resistant C57BL/6 parental strains. During early weeks of infection, these mice develop dominant Th2 type responses to L. major, although they eventually exhibit a Th2 to Th1 switch and spontaneously resolve their infections. In this study, we have examined the effects of either IL-12 or anti-TGF-β therapy on the immune response and course of disease in chronically infected CB6F1 mice. Local treatment with IL-12 inoculated into the parasitized lesion at 4 wk of infection induced a marked increase in IFN-γ production but did not result in a significant reduction in numbers of parasite or promote more rapid healing. However, local treatment with an Ab to TGF-β led to both a decrease in parasite numbers and more rapid healing, despite the fact that such treatment did not significantly alter the pattern of IL-4 and IFN-γ production. Immunohistochemical studies showed that anti-TGF-β treatment resulted in increased nitric oxide production within parasitized lesions. Our results suggest that TGF-β may play an important regulatory role during chronic stages of a L. major infection by suppressing macrophage production of nitric oxide and that, in the absence of TGF-β, even the relatively low levels of IFN-γ observed in mice with dominant Th2-type responses are sufficient to activate macrophages to destroy amastigotes within parasitized lesions.

Effects of the nature of adjuvant and site of parenteral immunization on the serum and mucosal immune responses induced by a nasal boost with a vaccine alone

Outbred OF1 mice were immunized subcutaneously with flu vaccine, either in the neck or in the lumbar region (back), in combination with adjuvants inducing either a Th1- or a Th2-type response, referred to as adjuvants A1 and A2, respectively. After two parenteral immunizations, the mice were boosted intranasally with nonadjuvanted vaccine. The serum response was analyzed after each immunization by measuring specific immunoglobulin A (IgA), IgG1, and IgG2a antibody levels, while the local response (same isotypes) was measured in the salivary glands after the mucosal boost by ELISPOTs. We observed that systemic priming at any of the two sites with a Th2 rather than a Th1 adjuvant dramatically enhanced the mucosal IgG1 and IgA responses following a mucosal boost with unadjuvanted vaccine. In addition, as judged by the IgG2a/IgG1 ratios and serum IgA levels, immunization of mice in the back induced a rise in Th2 response compared to neck immunization with adjuvant A1. In contrast, such back immunization with adjuvant A2 reversed the Th1-Th2 balance in favor of the Th1 response compared to neck immunization. Similar differences were observed in mucosal antibody levels according to the site of priming with one given adjuvant; priming in the back with adjuvant A1 increased the mucosal IgA and IgG1 responses compared to neck priming, while the local IgG2a levels were decreased. The reverse was true for adjuvant A2. Back versus neck priming with this latter adjuvant decreased the mucosal IgG1 response, while local IgG2a levels were increased. The different lymphatic drainages of the two sites of parenteral immunization may explain these differences, due to the targeting of particular lymphoid inductive sites. Some of these sites may represent crossroads between systemic and mucosal immunity.

CD86 (B7-2), but not CD80 (B7-1), expression in the epidermis of transgenic mice enhances the immunogenicity of primary cutaneous Candida albicans infections

Transgenic (Tg) mice whose epidermal keratinocytes constitutively overexpress either B7-1 (CD80) or B7-2 (CD86) exhibited exaggerated cutaneous delayed type hypersensitivity (DTH) to haptens compared to non-Tg mice. To determine whether enhanced DTH in these Tg mice is seen in response to cutaneous fungal infections, a primary infection with Candida albicans was established by inoculating this organism on the occluded skin of Tg and non-Tg mice. These infections resolved 7 days after removal of occlusive dressing in all three groups of mice, without evidence of exaggerated inflammation in either the Tg or non-Tg mice. Only B7-2 Tg mice developed enhanced Th1-lymphocyte-mediated immune responses to C. albicans antigens after resolving this infection: enhanced footpad swelling in response to intradermal C. albicans antigens, enhanced production of mRNA encoding Th1 lymphokines in draining lymph nodes, and increased gamma interferon secreted into culture supernatants by lymph node T lymphocytes stimulated with Candida antigens in vitro. Lastly, Western blotting of sera from mice that had resolved this fungal infection indicated that only B7-2 Tg mice recognized a wide range of Candida-associated antigens. These data suggest that these two costimulatory molecules, when expressed by keratinocytes, do not deliver identical signals to C. albicans antigen-reactive Th1 lymphocytes. The enhanced immune response in B7-2 Tg mice to a cutaneous C. albicans infection demonstrates the importance of antigen presentation and costimulation in immune reactivity to fungi. Furthermore, B7-2 Tg mice may be useful in identification of protective Candida antigens.

The role of IL-12 in the maintenance of an established Th1 immune response in experimental leishmaniasis

IL-12 initiates the development of cell-mediated immunity by promoting the differentiation of naive T cells into the Th1 phenotype, and is essential in the development of a Th1 immune response to the intracellular protozoan parasite, Leishmania major. The present study investigated whether IL-12 is also required for the maintenance and effector function of an established Th1 immune response in L. major-infected mice. While neutralization of IL-12 compromised the ability of a leishmanial antigen-reactive Th1 cell clone to produce IFN-gamma in vitro, lymph node cells taken from 2-week L. major-infected mice were able to secrete IFN-gamma in an IL-12-independent manner. However, when a short-term T cell line was established in vitro from lymph node cells, the production of IFN-gamma again became IL-12 dependent. These results suggest that other factors may compensate for IL-12 in vivo in promoting IFN-gamma production during L. major infection. To directly assess if IL-12 was required in vivo for resistance to L. major, we studied the effect of IL-12 neutralization on both a primary and secondary L. major infection in C3H mice. L. major infection in C3H mice is characterized by the development of a small lesion that heals by 8 weeks, and these animals are resistant to reinfection. As previously reported, administration of anti-IL-12 monoclonal antibody (mAb) during a primary infection led to severe disease. However, mice that had healed from a primary infection with L. major and were treated with anti-IL-12 mAb were as resistant as control animals. These findings suggest that once Th1 cells have developed, their effector function in vivo is independent of IL-12, and that this independence is not due to an intrinsic property of the T cell, but to the microenvironment created by the infection.

In vivo formation of electron paramagnetic resonance-detectable nitric oxide and of nitrotyrosine is not impaired during murine leishmaniasis

Recent studies have provided evidence for a dual role of nitric oxide (NO) during murine leishmaniasis. To explore this problem, we monitored the formation of NO and its derived oxidants during the course of Leishmania amazonensis infection in tissues of susceptible (BALB/c) and relatively resistant (C57BL/6) mice. NO production was detected directly by low-temperature electron paramagnetic resonance spectra of animal tissues. Both mouse strains presented detectable levels of hemoglobin nitrosyl (HbNO) complexes and of heme nitrosyl and iron-dithiol-dinitrosyl complexes in the blood and footpad lesions, respectively. Estimation of the nitrosyl complex levels demonstrated that most of the NO is synthesized in the footpad lesions. In agreement, immunohistochemical analysis of the lesions demonstrated the presence of nitrotyrosine in proteins of macrophage vacuoles and parasites. Since macrophages lack myeloperoxidase, peroxynitrite is likely to be the nitrating NO metabolite produced during the infection. The levels of HbNO complexes in the blood reflected changes occurring during the infection such as those in parasite burden and lesion size. The maximum levels of HbNO complexes detected in the blood of susceptible mice were higher than those of C57BL/6 mice but occurred at late stages of infection and were accompanied by the presence of bacteria in the cutaneous lesions. The results indicate that the local production of NO is an important mechanism for the elimination of parasites if it occurs before the parasite burden becomes too high. From then on, elevated production of NO and derived oxidants aggravates the inflammatory process with the occurrence of a hypoxic environment that may favor secondary infections.

Regional differences in the cellular immune response to experimental cutaneous or visceral infection with Leishmania donovani

Infection with the protozoan Leishmania donovani can cause serious visceral disease or subclinical infection in humans. To better understand the pathogenesis of this dichotomy, we have investigated the host cellular immune response to cutaneous or visceral infection in a murine model. Mice infected in the skin developed no detectable visceral parasitism, whereas intravenous inoculation resulted in hepatosplenomegaly and an increasing visceral parasite burden. Spleen cells from mice with locally controlled cutaneous infection showed strong parasite-specific proliferative and gamma interferon (IFN-gamma) responses, but spleen cells from systemically infected mice were unresponsive to parasite antigens. The in situ expression of IFN-gamma, interleukin-4 (IL-4), IL-10, IL-12, and inducible nitric oxide synthase (iNOS) mRNAs was determined in the spleen, draining lymph node (LN), and cutaneous site of inoculation. There was considerably greater expression of IFN-gamma and IL-12 p40 mRNAs in the LN draining a locally controlled cutaneous infection than in the spleen following systemic infection. Similarly, there was a high level of IFN-gamma production by LN cells following subcutaneous infection but no IFN-gamma production by spleen cells following systemic infection. Splenic IL-4 expression was transiently increased early after systemic infection, but splenic IL-10 transcripts increased throughout the course of visceral infection. IL-4 and IL-10 mRNAs were also increased in the LN following cutaneous infection. iNOS mRNA was detected earlier in the LN draining a cutaneous site of infection compared to the spleen following systemic challenge. Thus, locally controlled cutaneous infection was associated with antigen-specific spleen cell responsiveness and markedly increased levels of IFN-gamma, IL-12, and iNOS mRNA in the draining LN. Progressive splenic parasitism was associated with an early IL-4 response, markedly increased IL-10 but minimal IL-12 expression, and delayed expression of iNOS.

Leishmania major: a clone with low virulence for BALB/c mice elicits a Th1 type response and protects against infection with a highly virulent clone

BALB/c mice are highly susceptible to infection with Leishmania major and generally develop a severe, nonhealing form of disease following parasite inoculation. As opposed to protective Th1 type immune responses which develop in resistant strains of mice, BALB/c mice develop predominant Th2 type responses characterized by the production of high levels of IL-4, but only low levels of IFN-gamma. However, BALB/c mice will develop resistance and Th1 type responses following the inoculation of very low numbers of L. major promastigotes. In this study, we have examined the effects of parasite virulence on the immune response and disease phenotype in susceptible BALB/c mice. Two clones of L. major were isolated which differed with respect to their in vitro growth rates as promastigotes and their virulence for mice. One rapidly growing clone, L.m.F1, was highly virulent in BALB/c mice and produced nonhealing infections characterized by predominant Th2 type responses. In contrast, a slow-growing clone, L.m.S2, was less virulent in BALB/c mice and produced self-healing infections at parasite doses equivalent to those which produced progressive disease with the more virulent clone. Mice which healed infections with the L.m.S2 clone developed responses characterized by elevated production of IFN-gamma and were resistant to a challenge infection with the virulent L.m.F1 clone. These results suggest that the virulence of individual parasite clones may influence both the course of disease and the phenotype of the immune response which develops during infection.

Successful therapy of chronic, nonhealing murine cutaneous leishmaniasis with sodium stibogluconate and gamma interferon depends on continued interleukin-12 production

Treatment of nonhealing forms of human leishmaniasis with antimonial drugs in combination with gamma interferon (IFN-gamma) may promote healing more effectively than conventional drug therapy. Although the natures of immune responses in patients prior to treatment are often unclear, it is generally assumed that such therapy also promotes a switch from a Th2-type response to a dominant Th1-type response. We have examined the efficacy of IFN-gamma therapy, in combination with drug therapy, to promote healing and a Th2-to-Th1 switch in highly susceptible BALB/c mice infected with Leishmania major. Short-term treatment with the antileishmanial drug sodium stibogluconate failed to significantly alter the course of disease or the immune response when it was given during the third and fourth weeks of infection. IFN-gamma therapy, administered over the same time period, also failed to induce cure or a Th1 dominant response. In contrast, mice treated with a combination of drug and IFN-gamma therapy resolved their infections and developed Th1-type responses. However, administration of an antibody to interleukin 12 (IL-12) reversed the therapeutic effects of therapy with drug plus IFN-gamma, suggesting that IFN-gamma promotes cure through an IL-12-dependent mechanism. Analysis of mRNA levels within parasitized lesions suggests that drug treatment plus IFN-gamma treatment, in addition to reducing parasite numbers, results in reduced levels of IL-4, IL-10, and transforming growth factor beta transcripts but increased levels of transcripts of the p40 chain of IL-12 and inducible nitric oxide synthase, which catalyzes the production of nitric oxide. Together, these results suggest that such immunotherapy may promote the development of a protective Th1-type response in susceptible mice by a mechanism which involves both suppression of regulatory cytokines and enhancement of IL-12 and nitric oxide production.

Initial route of antigen administration alters the T-cell cytokine profile produced in response to the mouse pneumonitis biovar of Chlamydia trachomatis following genital infection

A Th1-type response develops following vaginal infection with the mouse pneumonitis biovar of Chlamydia trachomatis (MoPn). Since the type of response, i.e., Th1 versus Th2, can be influenced by factors present during T-cell activation, we examined the effects of different routes of MoPn administration on the cytokine profile and resistance against infection following a MoPn vaginal challenge. A dominant Th1-type cytokine profile developed in mice given live MoPn via the intranasal, oral, and vaginal routes with ratios of gamma interferon-secreting cells to interleukin 4-secreting cells greater than 10. In contrast, mice injected subcutaneously produced a Th2-type profile with a gamma interferon/interleukin 4 ratio of only 0.7. These mice also had significantly higher anti-MoPn immunoglobulin G1 serum titers, confirming a Th2-type cytokine profile. Exposure of mice to live MoPn, by any route prior to vaginal challenge, resulted in a shortened course of infection. However, the subcutaneous group resolved the vaginal infection more slowly, with 60% (6 of 10 mice) of the mice still isolation positive 12 days after challenge compared with only 20% of mice given live MoPn by other routes. Administration of UV-inactivated MoPn did not provide protection against a vaginal challenge. The decreased ability to clear infection was not associated with a shift in the cytokine profile, since intranasal and oral administration of UV-inactivated MoPn resulted in a predominant Th1-type response. Taken together, these data indicate that the initial route of MoPn administration can direct the type of response produced after a local MoPn infection and thus influence the ability of the immune response to protect against subsequent infection.

In vivo alterations in cytokine production following interleukin-12 (IL-12) and anti-IL-4 antibody treatment of CB6F1 mice with chronic cutaneous leishmaniasis

CB6F1 mice exhibit intermediate resistance to infection with Leishmania major compared to their highly susceptible (BALB/c) and resistant (C57BL/6) parental strains. Unlike the C57BL/6 and BALB/c strains, which rapidly develop dominant Th1- or Th2-type responses, respectively, after infection, CB6F1 mice develop responses in which both Th1- and Th2-type cytokines are elevated through at least the first month of infection before Th1 responses become dominant as cutaneous lesions gradually heal. We have examined the effects of interleukin-12 (IL-12) and/or anti-IL-4 antibody treatment on cytokine production and the course of disease in CB6F1 mice with chronic L. major infections. When administered at 1 month of infection, IL-12 treatment led to a rapid decrease in mRNA levels for IL-4 within parasitized lesions and a moderate increase in gamma interferon (IFN-gamma) transcript levels in lymph nodes draining the site of infection. When IL-12 and anti-IL-4 antibody were administered together, they induced a marked decrease in IL-4 and transforming growth factor beta mRNA expression within lesions and a more dramatic increase in lymph node IFN-gamma transcript levels within 4 days after treatment. In comparison, similar treatment of infected BALB/c mice led to only a moderate increase in IFN-gamma transcripts but no decrease in mRNA levels for Th2-type cytokines. Treatment of CB6F1 mice with either IL-12 or anti-IL-4 antibody had no significant effect on the subsequent course of infection, whereas combined IL-12 plus anti-IL-4 treatment resulted in a decrease in lesion size and parasite numbers and a shift towards a Th1-dominant response. These results suggest that the immediate effects of cytokine or anti-cytokine therapy may be predictive of the long-term effects on the course of infection and that down-regulation of Th-2 type cytokines may be critical to the development of a Th1-dominant response.

Modeling immunotherapy for allergy

Type I hypersensitivity, which functions to protect the organism from parasites, is caused by binding of antigen to IgE antibodies pre-attached to the cell surface of tissue mast cells and their circulating counterparts, the basophils. In "allergy," type I hypersensitivity is inappropriately induced by protein-based foreign substances (such as pollen) or protein components of insect stings, which in the normal course of events would be cleared from the organism without causing any damage. Paradoxically, a successful clinical treatment of allergy involves repeated immunization of allergic persons with low doses of the allergen--immunotherapy. Investigation of the available experimental evidence leads to the conclusion that the phenomena of immunotherapy are best addressed in terms of the interplay among the mechanism(s) of immune memory--Th1/Th2 cross-regulation--and the physical compartmentalization of the immune system. These conclusions are illustrated with a numerical simulation.

Invasion, control and persistence of Leishmania parasites

Significant advances in research on the immunopathogenesis of leishmaniasis include the discovery of novel putative evasion and survival strategies of Leishmania parasites, a more detailed understanding of the function and regulation of interleukin-12, definition of molecules involved in cognate interaction between macrophages and T cells and new ideas concerning the mechanisms of host resistance and susceptibility. The use of transgenic mice for (re)probing certain immunological aspects of leishmaniasis has yielded not only predictable and confirmatory but also unexpected and pioneering results which require critical appreciation.