Transgenic Expression of CXCR3 on T Cells Enhances Susceptibility to Cutaneous Leishmania major Infection by Inhibiting Monocyte Maturation and Promoting a Th2 Response

Cutaneous leishmaniasis, caused mainly by Leishmania major, an obligate intracellular parasite, is a disfiguring disease characterized by large skin lesions and is transmitted by a sand fly vector. We previously showed that the chemokine receptor CXCR3 plays a critical role in mediating resistance to cutaneous leishmaniasis caused by Leishmania major. Furthermore, T cells from L. major-susceptible BALB/c but not L. major-resistant C57BL/6 mice fail to efficiently upregulate CXCR3 upon activation. We therefore examined whether transgenic expression of CXCR3 on T cells would enhance resistance to L. major infection in susceptible BALB/c mice. We generated BALB/c and C57BL/6 transgenic mice, which constitutively overexpressed CXCR3 under a CD2 promoter, and then examined the outcomes with L. major infection. Contrary to our hypothesis, transgenic expression of CXCR3 (CXCR3^Tg) on T cells of BALB/c mice resulted in increased lesion sizes and parasite burdens compared to wild-type (WT) littermates after L. major infection. Restimulated lymph node cells from L. major-infected BALB/c-CXCR3^Tg mice produced more interleukin-4 (IL-4) and IL-10 and less gamma interferon (IFN-γ). Cells in draining lymph nodes from BALB/c-CXCR3^Tg mice showed enhanced Th2 and reduced Th1 cell accumulation associated with increased neutrophils and inflammatory monocytes. However, monocytes displayed an immature phenotype which correlated with increased parasite burdens. Interestingly, transgenic expression of CXCR3 on T cells did not impact the outcome of L. major infection in C57BL/6 mice, which mounted a predominantly Th1 response and spontaneously resolved their infection similar to WT littermates. Our findings demonstrate that transgenic expression of CXCR3 on T cells increases susceptibility of BALB/c mice to L. major.     

Dissociation of disease susceptibility, inflammation and cytokine profile in lmr1/2 congenic mice infected with Leishmania major

Severity of disease caused by Leishmania major depends on the genetics of the host. Early induction of T helper cell type 1 (Th1)-type responses in resistant C57BL/6 mice and T helper cell type 2 (Th2) in susceptible BALB/c mice is thought to determine cure or disease respectively. We have mapped three loci that confer susceptibility or resistance upon congenic mice on the C57BL/6 or BALB/c backgrounds. Here we examine the histopathology and production of interleukin 4 (IL-4) and interferon gamma (IFN-gamma) in the skin and draining lymph nodes in the congenic and parental mice. We show an evolving granuloma with a staged infiltration of inflammatory cells, but no difference between the groups. As an indication of an early-polarised Th1/Th2 response we measured IFN-gamma and IL-4 in the lymph nodes and found no difference between any of the mice during the first 48 h. During infection, the level of IL-4 correlated with the lesion size, indicating that IL-4 reflects the disease severity rather than controls it. Considering this effect, B6.C(lmr1,lmr2) mice had similar cytokine levels to the parental C57BL/6 mice despite increased susceptibility and C.B6(lmr1,lmr2) were similar to BALB/c despite increased resistance. We conclude that the lmr loci affect disease severity by a mechanism independent of conventional helper T-cell responses.     

Amastigote load and cell surface phenotype of infected cells from lesions and lymph nodes of susceptible and resistant mice infected with Leishmania major

Cells of the dendritic cell (DC) lineage, by their unique ability to stimulate naive T cells, may be of crucial importance in the development of protective immune responses to Leishmania parasites. The aim of this study was to compare the impact of L. major infection on DCs in BALB/c (susceptible, developing Th2 responses), C57BL/6 (resistant, developing Th1 responses), and tumor necrosis factor (TNF)(-/-) C57BL/6 mice (susceptible, developing delayed and reduced Th1 responses). We analyzed by immunohistochemistry the phenotype of infected cells in vivo. Granulocytes (GR1(+)) and macrophages (CD11b(+)) appear as the mainly infected cells in primary lesions. In contrast, cells expressing CD11c, a DC specific marker, are the most frequently infected cells in draining lymph nodes of all mice tested. These infected CD11c(+) cells harbored a particular morphology and cell surface phenotype in infected C57BL/6 and BALB/c mice. CD11c(+) infected cells from C57BL/6 and TNF(-/-) C57BL/6 mice displayed a weak parasitic load and a dendritic morphology and frequently expressed CD11b or F4/80 myeloid differentiation markers. In contrast, some CD11c(+) infected cells from BALB/c mice were multinucleated giant cells. Giant cells presented a dramatic accumulation of parasites and differentiation markers were not detectable at their surface. In all mice, lymph node CD11c(+) infected cells expressed a low major histocompatibility complex II level and no detectable CD86 expression. Our results suggest that infected CD11c(+) DC-like cells might constitute a reservoir of parasites in lymph nodes.     

Dendritic cell populations in Leishmania major-infected skin and draining lymph nodes

Using a metacyclic promastigote ear infection model of cutaneous leishmaniasis, we examined the phenotype, parasite load, and cytokine production of dendritic cells in the skin and draining lymph nodes of resistant C57BL/6J and susceptible BALB/c mice. Five dendritic cell populations were isolated from the skin and lymph nodes, and the main difference between the groups of mice was an increased number of plasmacytoid dendritic cells in the lymph nodes of the susceptible mice. Although similar cell types were present in the skin emigrants of both strains, there was a 10-fold larger number of cells in BALB/c mouse skin early in infection than in C57BL/6J mouse skin. None of the dendritic cells in the lymph nodes harbored parasites until 3 weeks after infection, with the Langerhans cells having the largest load and the plasmacytoid dendritic cells having the smallest load but the longest lasting infection. Although parasites could be detected in the lymph nodes a few hours after infection, none of the skin emigrants harbored parasites, indicating that they are not the vehicle that ferries the parasites from the skin to the lymph nodes. The presence of larger numbers of plasmacytoid cells in infected BALB/c mice, the more protracted infection of these cells, and their production of alpha interferon point to a complex and important role for the plasmacytoid cells in leishmaniasis.     

Resistance to Mycobacterium lepraemurium is correlated with the capacity to generate macrophage activating factor(s) in response to mycobacterial antigens in vitro.

The kinetics of cell-mediated immunity developed during the course of Mycobacterium lepraemurium infection were determined in resistant (C57BL) and susceptible (BALB/c) mice. Control of M. lepraemurium growth following footpad infection was T-cell dependent in C57BL mice as shown by the finding that T-cell deprived mice had enhanced bacterial counts in the footpad. In contrast, T-cell deprivation did not significantly alter the course of infection in BALB/c mice. However a T-cell dependent inflammatory response, resulting in an increase in size of the infected footpad, occurred in both strains, although it developed slightly later in BALB/c mice. Cells isolated from the lymph nodes, draining the infected foot-pads, were assayed for their proliferative responses to heat-killed M. lepraemurium (HK-MLM) antigens. Although lymph node cells from both mouse strains proliferated to HK-MLM early in the infection (1-2 weeks) both C57BL and BALB/c mice developed diminished in vitro proliferative reactivity within 4-6 weeks post-infection. Supernatants derived from cultures of lymph-node cells that had been stimulated with concanavalin A (Con A) or HK-MLM antigens, were assayed for the presence of macrophage-activating factor (MAF) activity using a tumour cytostasis assay and interferon (IFN) activity using a viral growth inhibition assay. Significantly higher levels of MAF and IFN were found in culture supernatants deprived from HK-MLM stimulated lymph-node cells from infected C57BL mice than from BALB/c mice during the first 8 weeks of infection. However, cells from infected mice of both strains produced similar amounts of both MAF and IFN in response to Con A.     

Different patterns of the L-histidine decarboxylase (HDC) gene expression in mice resistant and susceptible to experimental cutaneous leishmaniasis

Objective and design: In the present study the experimental murine Leishmania major (L. major) infection model was used to investigate the role of histamine biosynthesis in cutaneous leishmaniasis.Subjects, treatment and methods: A novel RNase Protection Assay (RPA) was developed and applied for the assessment of L-histidine decarboxylase (HDC) gene expression in organs of resistant C57BL/6 and susceptible BALB/c mice after infection with L. major.Results: In the acute phase of infection a rapid but transient induction of HDC expression was observed in the infected lymph nodes of both strains correlating both temporally and spatially with parasite spread. The signal was present in the draining popliteal lymph nodes of both hosts, however, only susceptible mice known to be unable to control parasite dissemination showed induction of HDC in their distant periaortic lymph nodes as well. During the chronic phase of infection only the heavily parasitized organs of BALB/c mice showed high HDC gene expression.Conclusions: These data suggest that expression of the histamine-producing enzyme HDC in the decisive acute phase of leishmaniasis is not coupled with development of either appropriate Th1 or inadequate Th2 responses to L. major. We hypothesize however, that during the chronic phase of infection elevated HDC levels, possibly of mast cell origin, are associated with Th2-dominated responses and serious disease development.Received 12 May 2003; returned for revision 3 July 2003; returned for final revision 11 September 2003; accepted by M. Parnham 24 September 2003     

Vaccination with the Leishmania infantum acidic ribosomal P0 protein plus CpG oligodeoxynucleotides induces protection against cutaneous leishmaniasis in C57BL/6 mice but does not prevent progressive disease in BALB/c mice

We have examined the efficacy of the administration in mice of a molecularly defined vaccine based on the Leishmania infantum acidic ribosomal protein P0 (rLiP0). Two different challenge models of murine cutaneous leishmaniasis were used: (i) subcutaneous inoculation of L. major parasites in susceptible BALB/c mice (a model widely used for vaccination analysis) and (ii) the intradermal inoculation of a low infective dose in resistant C57BL/6 mice (a model that more accurately reproduces the L. major infection in natural reservoirs and in human hosts). First, we demonstrated that C57BL/6 mice vaccinated with LiP0-DNA or rLiP0 protein plus CpG oligodeoxynucleotides (ODN) were protected against the development of dermal pathology and showed a reduction in the parasite load. This protection was associated with production of gamma interferon (IFN-γ) in the dermal site. Secondly, we showed that immunization with rLiP0 plus CpG ODN is able to induce only partial protection in BALB/c, since these mice finally developed a progressive disease. Further, we demonstrated that LiP0 vaccination induces a Th1 immunological response in both strains of mice. In both cases, the antibodies against LiP0 were predominantly of the immunoglobulin G2a isotype, which was correlated with an rLiP0-stimulated production of IFN-γ in draining lymph nodes. Finally, we demonstrated that LiP0 vaccination does not prevent the Th2 response induced by L. major infection in BALB/c mice. Taken together, these data indicate that the BALB/c model of cutaneous leishmaniasis may undervalue the potential efficacy of some vaccines based on defined proteins, making C57BL/6 a suitable alternative model to test vaccine candidates.     

Strain differences in mouse cellular responses to Mycobacterium lepraemurium and BCG subcutaneous infections. I. Analysis of cell surface phenotype in local granulomas.

C57BL/6, BALB/c and CBA mice were subcutaneously infected with either Mycobacterium lepraemurium (MLM) or BCG, and studied for bacillary growth, granuloma size of infected footpads and draining lymph nodes (DLN), and DLN cell surface phenotype. Whereas, BCG-infected mice controlled the infection and developed early and large granulomas, MLM-infected mice exhibited major strain variations in their resistance to the infection, as well as in the granuloma size and kinetics. C57BL/6 mice, highly resistant, displayed early and regressive granulomas; BALB/c mice showed lower resistance and early granulomas that grew continuously; CBA mice, highly susceptible, developed late, soft, phagocyte-rich granulomas. Important strain differences in lymph node lymphocyte subset distribution could be observed prior to any infection: C57BL/6 mice displayed higher B cell percentages than both of the other strains and BALB/c mice showed the highest CD4/CD8 ratios, followed by CBA and C57BL/6 mice. BCG and MLM infections both induced similar changes of these parameters in all three strains: that is a decrease of the B cell percentage and a decrease of the CD4/CD8 ratio, and the strain differences observed in uninfected mice persisted. On the other hand, DLN cells stimulated by the infecting bacillus and interleukin 2 also displayed an increase of the CD8 T cell percentage as compared with normal lymph node cells, but this phenomenon was much less pronounced in BALB/c mice, whether infected by MLM or BCG, and in MLM-infected CBA mice, than in BCG- or MLM-infected C57BL/6 (B6) mice. Thus the ability of C57BL/6 mice to generate an early and persistent CD8 T cell response to mycobacteria may contribute to their resistance to MLM.     

In susceptible mice,Leishmania major induce very rapid interleukin-4 production by CD4+ T cells which are NK1.1−

Susceptibility of BALB/c mice to infection with Leishmania major is associated with a T helper type 2 (Th2) response. Since interleukin-4 (IL-4) is critically required early for Th2 cell development, the kinetics of IL-4 mRNA expression was compared in susceptible and resistant mice during the first days of infection. In contrast to resistant mice, susceptible mice exhibited a peak of IL-4 mRNA in their spleens 90 min after i.v. injection of parasites and in lymph nodes 16 h after s.c. injection. IL-12 and interferon-γ (IFN-γ) down-regulated this early peak of IL-4 mRNA; the effect of IL-12 was IFN-γ dependent. Treatment of resistant C57BL/6 mice with anti-IFN-γ allowed the expression of this early IL-4 response to L. major. The increased IL-4 mRNA expression occurred in Vβ8, 7, 2^? CD4⁺ cells in BALB/c mice and NK1.1^? CD4⁺ cells in anti-IFN-γ treated C57BL/6 mice. These results show that the NK1.1⁺ CD4⁺ cells, responsible for the rapid burst of IL-4 production after i.v. injection of anti-CD3, do not contribute to the early IL-4 response to L. major.     

Ineffective cellular immune response associated with T-cell apoptosis in susceptible Mycobacterium bovis BCG-infected mice

It has previously been reported that inhibition of delayed-type hypersensitivity-mediating functions of T cells during mycobacterial infection in mice is haplotype dependent. In the present study, we show that Mycobacterium bovis BCG infection induced, in susceptible C57BL/6 and BALB/c mice but not in resistant C3H/HeJ and DBA/2 mice, an important splenomegaly. An in vitro defect in T-cell proliferation in response to T-cell receptor (TCR) stimulation with mitogens or anti-CD3 antibodies was associated with enhanced levels of CD4(+) and CD8(+) T-cell apoptosis in susceptible but not in resistant mice 2 weeks after infection. Further investigations of C57BL/6 and C3H/HeJ mice revealed that in vivo splenomegaly was associated with destruction of the lymphoid tissue architecture, liver cellular infiltrates, and increased numbers of apoptotic cells in both spleen and liver tissue sections. Infection of C57BL/6 mice but not of C3H/HeJ mice induced massive production of tumor necrosis factor alpha (TNF-alpha) in serum, as well as an increase in Fas and Fas ligand (FasL) expression in T cells. In vitro addition of neutralizing anti-TNF-alpha antibodies led to a significant reduction in CD3-induced T-cell apoptosis of both CD4(+) and CD8(+) T cells of C57BL/6 mice, while the blockade of Fas-FasL interactions reduced apoptosis only in CD4(+) but not in CD8(+) T cells. Together, these results suggest that TNF-alpha and Fas-FasL interactions play a role in the activation-induced cell death (AICD) process associated with a defect in T-cell proliferation of the susceptible C57BL/6 mice. T-cell death by apoptosis may represent one of the important components of the ineffective immune response against mycobacterium-induced immunopathology in susceptible hosts.     

Immune responses associated with susceptibility of C57BL/10 mice to Leishmania amazonensis.

Leishmaniae are protozoans which, depending upon both the host and parasite species, can cause either a healing or nonhealing infection. While C57BL/10 mice are able to heal following infection with Leishmania major, they fail to heal following infection with Leishmania amazonensis. In order to address the role of Th1 and Th2 cell responses in the outcome of these infections in C57BL/10 mice, gamma interferon (IFN-gamma) and interleukin-4 (IL-4) production was assessed. While cells from L. major-infected C57BL/10 mice produced high levels of IFN-gamma, cells from L. amazonensis-infected animals produced little or no IFN-gamma. On the other hand, IL-4 was produced only by cells from L. amazonensis-infected C57BL/10 mice, but this production was restricted to the first few weeks of infection. Later in infection, when lesions were evident, no IL-4 was detected. Treatment of BALB/c mice with a monoclonal antibody (11B11) directed against IL-4 induced a dramatic reduction in L. amazonensis lesions. This reduction was associated with a decrease in IL-4 levels and an increase in IFN-gamma production. However, only a slight reduction in lesion sizes and parasite numbers was observed when anti-IL-4-treated C57BL/10 mice were infected with L. amazonensis. These results suggest that IL-4 may have an important role in mediating susceptibility to L. amazonensis in BALB/c mice, as previously demonstrated for L. major. More importantly, however, the data suggest that susceptibility to L. amazonensis in C57BL/10 mice is due to the absence of a Th1 cell response, rather than to the presence of a Th2 cell response.     

Cryptosporidium infection in major histocompatibility complex congeneic strains of mice: variation in susceptibility and the role of T-cell cytokine responses

Studies with murine infection models have shown that immunity to the protozoan parasite Cryptosporidium involves T-cells and interferon-gamma (IFN-γ) activity. The present study was performed to compare the course of infection of Cryptosporidium muris in major histocompatibility complex (MHC) congeneic strains of mice and examine the relationship between susceptibility to infection and production of T-cell cytokines. In experiments with BALB mice, the BALB/c strain (H-2 ^d) produced significantly fewer oocysts and recovered from infection sooner than the BALB/B (H-2 ^b) or BALB/K (H-2 ^k) strains. BALB/B X BALB/c F1 hybrid mice were found to express the more susceptible phenotype of the BALB/B parent strain, indicating that the gene(s) in the H-2 locus conferring increased susceptibility to C. muris infection was dominant. At different times during infection of the resistant BALB/c strain and the susceptible BALB/B strain, splenocytes were cultured with soluble parasite antigen and measurements were made of production of a number of T-cell cytokines. Similar patterns of increasing levels of IFN-γ and interleukin 2 (IL-2) were observed in both the resistant and susceptible strains during the patent stage of infection, indicating that production of these type 1 T-helper-cell (TH1) cytokines (i.e. involved in cell-mediated responses) correlated with the development of immunity. This also suggested that the increased susceptibility of BALB/B mice was not associated with a defective TH1 cytokine response. In the study of TH2 cytokines (involved in induction of an antibody response), low levels of IL-10 were detected during infection of BALB/c and BALB/B mice. In contrast, although IL-4 was released by splenocytes of both strains, significantly larger amounts were obtained from cells of the susceptible BALB/B mice in the early stages of infection. Thus, the H-2-dependent variation in susceptibility to infection between these BALB strains correlated with a difference in the pattern of IL-4 secretion. Received: 11 July 1996 / Accepted: 15 September 1996     

Pretreatment with recombinant Flt3 ligand partially protects against progressive cutaneous leishmaniasis in susceptible BALB/c mice

Dendritic cells are potent antigen-presenting cells that also produce interleukin-12 (IL-12) during innate and adaptive cellular immune responses and that thereby promote the differentiation of gamma interferon (IFN-gamma)-producing Th1-type CD4(+) T lymphocytes. We hypothesized that expanded dendritic-cell populations in mice pretreated with the hematopoietic cytokine Flt3L would protect against cutaneous Leishmania major infection. Pretreatment of disease-susceptible BALB/c mice with 10 microg of recombinant Flt3L (rFlt3L) for 9 to 10 days before infection increased lymph node IL-12 p40 productive capacity 20-fold compared to that of saline-injected controls. Furthermore, 9 of 22 (40.9%) rFlt3L-pretreated BALB/c mice resolved their cutaneous infections, whereas none of the 22 control BALB/c mice healed. Healed, rFlt3L-pretreated mice did not develop disease following reinfection. Flt3L pretreatment also reduced parasite numbers 1,000-fold in the cutaneous lesions at 2 weeks after infection relative to numbers in lesions of untreated controls. However, Flt3L pretreatment did not significantly alter L. major-induced IFN-gamma and IL-4 production in lymph node culture at 1, 2, and 4 weeks after infection. Despite the lack of Th immune deviation, Flt3L ligand-pretreated lymph nodes expressed up to 10-fold higher levels of IL-12 p40 and inducible (type 2) nitric oxide synthase mRNA at 7 days after infection. In contrast, treatment with rFlt3L after infection failed to protect against disease despite comparable expansions of dendritic cells and IL-12 p40 productive capacity in both infected and uninfected BALB/c mice treated with rFlt3L. We conclude that rFlt3L pretreatment before infection with L. major reduces parasite load and promotes healing of cutaneous lesions without stable cytokine deviation towards a dominant Th1 cytokine phenotype.     

Immunomodulatory Properties of Borage (<Emphasis Type="BoldItalic">Echium amoenum</Emphasis>) on BALB/c Mice Infected with <Emphasis Type="BoldItalic">Leishmania major</Emphasis>

Leishmaniasis is caused by parasitic protozoa transmitted by the bite of a female sand fly and is currently endemic in 88 countries. BALB/c mice are highly susceptible to the infection with the parasite Leishmania major, and this susceptibility has been attributed, in part, to the expansion of Th2 cells, production of their cytokines, and downregulation of Th1 cytokine, interferon gamma (IFN-γ). In this report, we used both aqueous and alcoholic extracts of Iranian borage (Echium amoenum Fisch & C.A. Mey) for treatment of L. major infection in BALB/c mice. We found that both extracts had immunomodulatory properties and increased the level of IFN-γ and lowered the parasite burden in the proximal lymph nodes and prevented the necrosis of the footpad as compared with the untreated infected mice. These results may provide a basis for further studies directed toward the use of the Iranian borage against L. major infection.     

Murine immune response induced by Leishmania major during the implantation of paraffin tablets

We carried out a model of chronic inflammation using a subcutaneous paraffin tablet in mice experimentally infected with Leishmania major. It was previously reported that the parasite load following paraffin implantation occurred at a peak of 21 days in both BALB/c and C57BL/6 mice. At the present study, we have investigated what cytokines and chemokines are directly related to the parasite load in C57BL/6 mice. All mice were divided in four groups: mice implanted with paraffin tablets; mice experimentally infected with L. major; mice implanted with paraffin tablets and experimentally infected with L. major; and mice submitted only to the surgery were used for the Real-Time Polymerase Chain Reaction (RT-PCR) controls. Fragments of skin tissue and the tissue surrounding the paraffin tablets (inflammatory capsule) were collected for histopathology and RT-PCR studies. By 21 days, a diffuse chronic inflammatory reaction was mainly observed in the deep dermis where macrophages parasitized with Leishmania amastigotes were also found. RT-PCR analysis has shown that BALB/c mice showed strong IL-4 and IL-10 mRNA expression than controls with very little expression of IFN-γ. In contrast, both IFN-γ and IL-10 mRNA was found in higher levels in C57BL/6 animals. Moreover, in C57BL/6 mice the expression of chemokines mRNA of CCL3/MIP-1α was more highly expressed than CCL2/MCP-1. We conclude that the Th1 immune response C57BL/6 did not change to a Th2 response, even though C57BL/6 animals presented higher parasitism than BALB/c mice 21 days after infection and paraffin implantation.     

Influence of the genetic background and parasite load of mice on the immune response developed against nymphs of Ixodes ricinus

The immune response of BALB/c (H-2d), DBA (H-2d), C57BL/6 (H-2b), C3H (H-2k), CBA (H-2k), SJL (H-2s), and FVB (H-2q) mice infested once with 15 nymphs of Ixodes ricinus is polarized toward Th2 as suggested by cytokines produced by lymph node cells stimulated with concanavalin A. The parasite load does not influence the polarization of the immune response as observed in BALB/c mice, which developed a Th2 response when infested with 5 or 45 nymphs. As assessed by attachment and weights of engorged nymphs, no resistance was acquired by BALB/c, C57BL/6, or C3H mice undergoing three successive infestations. However, these mice produced a gradual increase in IgE. Received: 8 December 1998 / Accepted: 22 December 1998     

The induction of a protective response in Leishmania major-infected BALB/c mice with anti-CD40 mAb

A protective immune response to the intracellular parasite Leishmania major requires the development of a Th1 CD4⁺ T cell phenotype. We demonstrate herein that BALB/c mice, which normally develop a susceptible Th2 response to L. major infection, are protected when co-injected with an agonistic anti-murine CD40 mAb. Anti-CD40 mAb-mediated protection in this system was found to be T cell dependent, since it was not observed in C57BL/ 6 × 129 mice that were rendered T cell deficient (TCR β^–/– × TCR δ^–/–) and L. major susceptible. Anti-CD40 mAb stimulation of L. major-infected BALB/c mice was accompanied by increased IL-12 and IFN-γ production in draining lymphnodes, analyzed either by direct expression, or in an antigen-specific in vitro recall assay. The protective role of these cytokines was indicated by the finding that anti-CD40 mAb-mediated protection of L. major-infected BALB/c mice could be reversed by co-treating the animals with neutralizing anti-IL-12 and/or anti-IFN-γ mAb. Collectively, these data suggest that BALB/c mice develop a protective Th1 CD4⁺ T cell response to L. major infection when co-injected with anti-CD40 mAb. While the CD40-CD40L interaction has been previously shown to be vital in the control of murine Leishmaniasis, the current study establishes in vivo that anti-CD40 mAb treatment alone is sufficient to protect BALB/c mice from L. majorinfection and raises the possibility of utilizing this approach for vaccination strategies.     

Early Gene Expression of NK Cell-Activating Chemokines in Mice Resistant to Leishmania major

Susceptibility of mice to Leishmania major is associated with an insufficient NK cell-mediated innate immune response. We analyzed the expression of NK cell-activating chemokines in vivo during the first days of infection in resistant and susceptible mice. The mRNA expression of gamma interferon-inducible protein 10 (IP-10), monocyte chemoattractant protein 1 (MCP-1), and lymphotactin was upregulated 1 day after infection in the draining lymph nodes of resistant C57BL/6 mice but not in those of susceptible BALB/c mice. In vivo local treatment of BALB/c mice with recombinant IP-10 shortly after infection resulted in an enhanced NK cell activity in the draining lymph node. The data suggest that although the recruitment of NK cells is normal in susceptible mice, the lack of NK cell-activating chemokines is a factor resulting in a suboptimal NK cell-mediated defense.