Pattern of macrophage activation in yersinia-resistant and yersinia-susceptible strains of mice

Th1 cells, in cooperation with activated macrophages, are required to overcome Yersinia enterocolitica infection in mice. The pathway macrophages utilize to metabolize arginine can alter the outcome of inflammation in different ways. The objective of this study was to verify the pattern of macrophages activation in Y. enterocolitica infection of BALB/c (Yersinia-susceptible) and C57BL/6 (Yersinia-resistant) mice. Both strains of mice were infected with Y. enterocolitica O:8 WA 2707. Peritoneal macrophages and spleen cells were obtained on the 1st, 3rd and 5th day post-infection. The iNOS and the arginase activities were assayed in supernatants of macrophage cultures, by measuring their NO/citrulline and ornithine products, respectively. TGFbeta-1 production was also assayed. The Th1 and Th2 responses were evaluated in supernatants of lymphocyte cultures, by IFN-gamma and IL-4 production. Our results showed that in the early phase of Y. enterocolitica infection (1st and 3rd day), the macrophages from C57BL/6 mice produced higher levels of NO/citrulline and lower levels of ornithine than macrophages from BALB/c mice. The infection with Y. enterocolitica leads to an increase in the TGF-beta1 and IL-4 production by BALB/c mice and to an increase in the IFN-gamma levels produced by C57BL/6 mice. These results suggest that Y. enterocolitica infection leads to the modulation of M1 macrophages in C57Bl/6 mice, and M2 macrophages in BALB/c mice. The predominant macrophage population (M1 or M2) at the 1st and 3rd day of infection thus seems to be important in determining Y. enterocolitica susceptibility or resistance.     

IFN-gamma-dependent nitric oxide production is not linked to resistance in experimental African trypanosomiasis

Resistance to African trypanosomes is dependent on B cell and Th1 cell responses to the variant surface glycoprotein (VSG). While B cell responses to VSG control levels of parasitemia, the cytokine responses of Th1 cells to VSG appear to be linked to the control of parasites in extravascular tissues. We have recently shown that IFN-gamma knockout (IFN-gamma KO) mice are highly susceptible to infection and have reduced levels of macrophage activation compared to the wild-type C57BL/6 (WT) parent strain, even though parasitemias were controlled by VSG-specific antibody responses in both strains. In the present work, we examine the role of IFN-gamma in the induction of nitric oxide (NO) production and host resistance and in the development of suppressor macrophage activity in mice infected with Trypanosoma brucei rhodesiense. In contrast to WT mice, susceptible IFN-gamma KO mice did not produce NO during infection and did not develop suppressor macrophage activity, suggesting that NO might be linked to resistance but that suppressor cell activity was not associated with resistance or susceptibility to trypanosome infection. To further examine the consequence of inducible NO production in infection, we monitored survival, parasitemia, and Th cell cytokine production in iNOS KO mice. While survival times and parasitemia of iNOS KO mice did not differ significantly from WT mice, VSG-specific Th1 cells from iNOS KO mice produced higher levels of IFN-gamma and IL-2 than cells from WT mice. Together, these results show for the first time that inducible NO production is not the central defect associated with susceptibility of IFN-gamma KO mice to African trypanosomes, that IFNgamma-induced factors other than iNOS may be important for resistance to the trypanosomes, and that suppressor macrophage activity is not linked to either the resistance or the susceptibility phenotypes.     

Innate resistance to experimental African trypanosomiasis: differences in cytokine (TNF-alpha, IL-6, IL-10 and IL-12) production by bone marrow-derived macrophages from resistant and susceptible mice

Resistance to African trypanosomiasis is under multigenic control. BALB/c mice are highly susceptible while C57Bl/6 mice are relatively resistant. Macrophages eliminate opsonized trypanosomes from the bloodstream and are involved in immunosuppression. We therefore investigated the production of a number of cytokines (IL-10, IL-6, TNF-alpha and IL-12) by bone marrow-derived macrophages (BMDM) from C57Bl/6 and BALB/c mice following challenge with either Trypanosoma congolense or Trypanosoma brucei. BMDM from C57Bl/6 mice, upon challenge with whole cell extracts (WCE) of T. congolense or T. brucei, produced significantly more TNF-alpha and IL-12 than those from BALB/c mice. The production of these cytokines was significantly enhanced by pretreatment of the cells with IFN-gamma. BMDM from BALB/c mice, however, produced significantly more IL-6 and IL-10 than those from C57Bl/6 mice. In contrast to LPS stimulation, simultaneous treatment of cells with WCE and IFN-gamma enhanced IL-10 synthesis by BMDM from BALB/c mice. These results indicate that cytokine genes are differentially regulated in macrophages from trypanosome-susceptible and -resistant mice and are consistent with our previous findings wherein retrovirus-immortalized macrophage cell lines from BALB/c and C57Bl/6 mice produce differential amounts of cytokines after phagocytosis of trypanosomes.     

Immune evasion by Helicobacter pylori is mediated by induction of macrophage arginase II

Helicobacter pylori infection persists for the life of the host due to the failure of the immune response to eradicate the bacterium. Determining how H. pylori escapes the immune response in its gastric niche is clinically important. We have demonstrated in vitro that macrophage NO production can kill H. pylori, but induction of macrophage arginase II (Arg2) inhibits inducible NO synthase (iNOS) translation, causes apoptosis, and restricts bacterial killing. Using a chronic H. pylori infection model, we determined whether Arg2 impairs host defense in vivo. In C57BL/6 mice, expression of Arg2, but not arginase I, was abundant and localized to gastric macrophages. Arg2(-/-) mice had increased histologic gastritis and decreased bacterial colonization compared with wild-type (WT) mice. Increased gastritis scores correlated with decreased colonization in individual Arg2(-/-) mice but not in WT mice. When mice infected with H. pylori were compared, Arg2(-/-) mice had more gastric macrophages, more of these cells were iNOS(+), and these cells expressed higher levels of iNOS protein, as determined by flow cytometry and immunofluorescence microscopy. There was enhanced nitrotyrosine staining in infected Arg2(-/-) versus WT mice, indicating increased NO generation. Infected Arg2(-/-) mice exhibited decreased macrophage apoptosis, as well as enhanced IFN-γ, IL-17a, and IL-12p40 expression, and reduced IL-10 levels consistent with a more vigorous Th1/Th17 response. These studies demonstrate that Arg2 contributes to the immune evasion of H. pylori by limiting macrophage iNOS protein expression and NO production, mediating macrophage apoptosis, and restraining proinflammatory cytokine responses.     

Induction of autophagy correlates with increased parasite load of Leishmania amazonensis in BALB/c but not C57BL/6 macrophages

We investigated the role of autophagy in infection of macrophages by Leishmania amazonensis. Induction of autophagy by IFN-γ or starvation increased intracellular parasite load and the percentages of infected macrophages from BALB/c but not from C57BL/6 mice. In contrast, starvation did not affect the replication of either Leishmania major or Trypanosoma cruzi in BALB/c macrophages. In BALB/c macrophages, starvation resulted in increased monodansylcadaverine staining and in the appearance of double-membrane and myelin-like vesicles characteristic of autophagosomes. Increased parasite load was associated with a reduction in NO levels and was attenuated by wortmannin, an inhibitor of autophagy. In infected macrophages from BALB/c, but not from C57BL/6 mice, starvation increased the number of lipid bodies and the amounts of PGE₂ produced. Exogenous PGE₂ increased parasite load in macrophages from BALB/c, but not C57BL/6 mice. The cyclooxygenase inhibitor indomethacin prevented the increase of parasite load in starved BALB/c macrophages, and actually induced parasite killing. These results suggest that autophagy regulates the outcome of L. amazonensis infection in macrophages in a host strain specific manner.     

Mouse genotype affects inducible expression of cytokine genes.

The levels of circulating IFN in mice infected with Newcastle disease virus (NDV) are regulated by the If-1 locus. In this study we show that in NDV-infected C57BL/6 mice, which carry the If-1h allele and produce high levels of IFN, high levels of both IFN-alpha and -beta mRNA can be detected in the spleen. In contrast, only very low levels of IFN mRNA could be detected in spleens of infected BALB/c mice containing the If-1l allele and producing low levels of IFN or in B6.C-H28c mice that are congenic for the If-1l allele. The relative levels of all individual IFN-alpha 1, alpha 4, and alpha 6 mRNA in spleens of infected BALB/c were lower than in spleens of infected C57BL/6 mice, indicating that the If-1 locus affects the expression of all IFN-alpha subtypes and is not associated with the deletion or inactivation of a specific IFN gene. The relative levels of IFN regulatory factor-1 mRNA in infected mice carrying the If-1l and If-1h loci were comparable, suggesting that the If-1 regulation is not associated with the altered expression of the IFN regulatory factor-1 gene. Quantitative difference in the expression of IFN-alpha and -beta genes was also observed in in vitro-infected peritoneal macrophages isolated from either C57BL/6 or BALB/c mice. A surprise finding was that the If-1 locus also affected the NDV-induced expression of two other cytokine genes, TNF-alpha and IL-6. Priming of the macrophage cultures with murine IFN enhanced the expression of all cytokine genes, and the relative levels of IFN, TNF-alpha, and IL-6 mRNA induced by NDV in macrophages derived from C57BL/6 and BALB/c mice were comparable. We propose that the If-1 locus affects the early stages of a signal transduction pathway which are common to the virus-mediated induction of IFN, TNF-alpha, and IL-6 genes.     

Effects of iNOS inhibitor on IFN-gamma production and apoptosis of splenocytes in genetically different strains of mice infected with Toxoplasma gondii

To evaluate the role of nitric oxide (NO) in IFN-gamma production and apoptosis of splenocytes in genetically different strains of mice with toxoplasmosis, BALB/c (a toxoplasmosis resistant strain) and C57BL/6 (a toxoplasmosis susceptible strain) mice were infected with Toxoplasma gondii cysts orally and subsequently injected intraperitoneally with aminoguanidine, an iNOS inhibitor (AG; 35 mg/kg per mouse daily for 14 days). When BALB/c or C57BL/6 mice were infected with T. gondii without AG treatment, number of brain cysts, NO and IFN-gamma production by splenocytes, and percentages of apoptotic splenocytes were increased compared to uninfected control mice without AG treatment. AG treatment increased the number of brain cysts, and reduced NO and IFN-gamma production in T. gondii-infected C57BL/6 mice. In contrast, in T. gondii-infected BABL/c mice, the number of brain cysts, and NO and IFN-gamma production of splenocytes was not altered by treatment with AG. However, the percentages of apoptotic splenocytes in T. gondii-infected BALB/c or C57BL/6 mice were not affected by AG treatment. These results suggest that NO modulates IFN-gamma production in T. gondii-infected C57BL/6 mice, and that NO is involved in mediating a protective response in toxoplasmosis susceptible, but not resistant, mice strain during acute infection.     

M-1/M-2 macrophages and the Th1/Th2 paradigm

Evidence is provided that macrophages can make M-1 or M-2 responses. The concept of M-1/M-2 fomented from observations that macrophages from prototypical Th1 strains (C57BL/6, B10D2) are more easily activated to produce NO with either IFN-gamma or LPS than macrophages from Th2 strains (BALB/c, DBA/2). In marked contrast, LPS stimulates Th2, but not Th1, macrophages to increase arginine metabolism to ornithine. Thus, M-1/M-2 does not simply describe activated or unactivated macrophages, but cells expressing distinct metabolic programs. Because NO inhibits cell division, while ornithine can stimulate cell division (via polyamines), these results also indicate that M-1 and M-2 responses can influence inflammatory reactions in opposite ways. Macrophage TGF-beta1, which inhibits inducible NO synthase and stimulates arginase, appears to play an important role in regulating the balance between M-1 and M-2. M-1/M-2 phenotypes are independent of T or B lymphocytes because C57BL/6 and BALB/c NUDE or SCID macrophages also exhibit M-1/M-2. Indeed, M-1/M-2 proclivities are magnified in NUDE and SCID mice. Finally, C57BL/6 SCID macrophages cause CB6F1 lymphocytes to increase IFN-gamma production, while BALB/c SCID macrophages increase TGF-beta production. Together, the results indicate that M-1- or M-2-dominant macrophage responses can influence whether Th1/Th2 or other types of inflammatory responses occur.     

Toxoplasma gondii: The severity of toxoplasmic encephalitis in C57BL/6 mice is associated with increased ALCAM and VCAM-1 expression in the central nervous system and higher blood-brain barrier permeability

In order to investigate the differential ALCAM, ICAM-1 and VCAM-1 adhesion molecules mRNA expression and the blood-brain barrier (BBB) permeability in C57BL/6 and BALB/c mice in Toxoplasma gondii infection, animals were infected with ME-49 strain. It was observed higher ALCAM on day 9 and VCAM-1 expression on days 9 and 14 of infection in the central nervous system (CNS) of C57BL/6 compared to BALB/c mice. The expression of ICAM-1 was high and similar in the CNS of both lineages of infected mice. In addition, C57BL/6 presented higher BBB permeability and higher IFN-γ and iNOS expression in the CNS compared to BALB/c mice. The CNS of C57BL/6 mice presented elevated tissue pathology and parasitism. In conclusion, our data suggest that the higher adhesion molecules expression and higher BBB permeability contributed to the major inflammatory cell infiltration into the CNS of C57BL/6 mice that was not efficient to control the parasite.     

Anthrax Lethal Toxin Kills Macrophages in a Strain-Specific Manner by Apoptosis or Caspase-1-Mediated Necrosis

Murine macrophages have been classified as either susceptible or nonsusceptible to killing by anthrax lethal toxin (LT) depending upon genetic background. While considered resistant to LT killing, we found that bone marrow-derived macrophages (BMMs) from DBA/2, AKR, and C57BL/6 mice were slowly killed by apoptosis following LT exposure. LT killing was not restricted to in vitro assays, as splenic macrophages were also depleted in LT-injected C57BL/6 mice. Human macrophages, also considered LT resistant, similarly underwent slow apoptosis in response to LT challenge. In contrast, LT triggered rapid necrosis and a broad protein release in BMMs derived from BALB/c and C3H/HeJ, but not C57BL/6 mice. Released proteins included processed interleukin-18, confirming reports of inflammasome and caspase-1 activation in LT-mediated necrosis in macrophages. Complete inhibition of caspase-1 activity was required to block LT-mediated necrosis. Strikingly, minimal residual caspase-1 activity was sufficient to trigger significant necrosis in LT-treated macrophages, indicating the toxicity of caspase-1 in this process. IL-18 release does not trigger cytolysis, as IL-18 is released late and only from LT-treated macrophages undergoing membrane perturbation. We propose that caspase-1-mediated macrophage necrosis is the source of the cytokine storm and rapid disease progression reported in LT-treated BALB/c mice.     

Inhibition of inducible nitric oxide synthase exacerbates chronic cerebral toxoplasmosis in Toxoplasma gondii-susceptible C57BL/6 mice but does not reactivate the latent disease in T. gondii-resistant BALB/c mice

Infection of C57BL/6 mice with Toxoplasma gondii leads to progressive and ultimately fatal chronic Toxoplasma encephalitis (TE). Genetic deletion or inhibition of inducible nitric oxide synthase (iNOS) from the beginning of infection increased the number of T. gondii cysts in the brain and markedly reduced the time-to-death in this mouse strain. In the present study, we addressed whether iNOS also contributes to the control of intracerebral parasites in a clinically stable latent infection that develops in T. gondii-resistant BALB/c mice after resolution of the acute phase of TE. iNOS was expressed in the inflammatory cerebral infiltrates of latently infected BALB/c mice, but the number of iNOS+ cells was significantly lower than in the brains of chronically infected T. gondii-susceptible C57BL/6 mice. In BALB/c mice with latent TE (> 30 days of infection), treatment with the iNOS inhibitors L-N6-iminoethyl-lysine or L-nitroarginine-methylester for < or = 40 days did not result in an increase of the intracerebral parasitic load and a reactivation of the disease, despite the presence of iNOS-suppressive inhibitor levels in the brain. However, L-nitroarginine-methylester treatment had remarkably toxic effects and induced a severe wasting syndrome with high mortality. In contrast to BALB/c mice, L-N6-iminoethyl-lysine treatment rapidly exacerbated the already established chronic TE of C57BL/6 mice. Thus, the containment of latent toxoplasms in T. gondii-resistant BALB/c mice is independent of iNOS, whereas the temporary control of intracerebral parasites in T. gondii-susceptible C57BL/6 mice with chronic TE requires iNOS activity.     

Arginase modulates Salmonella induced nitric oxide production in RAW264.7 macrophages and is required for Salmonella pathogenesis in mice model of infection

Arginine is a common substrate for both inducible nitric oxide synthase (iNOS) and arginase. The competition between iNOS and arginase for arginine contributes to the outcome of several parasitic and bacterial infections. Salmonella infection in macrophage cell line RAW264.7 induces iNOS. Because the availability of l-arginine is a major determinant for nitric oxide (NO) synthesis, we hypothesize that in the Salmonella infected macrophages NO production may be regulated by arginase. Here we report for the first time that Salmonella up-regulates arginase II but not arginase I isoform in RAW264.7 macrophages. Blocking arginase increases the substrate l-arginine availability to iNOS for production of more nitric oxide and perhaps peroxynitrite molecules in the infected cells allowing better killing of virulent Salmonella in a NO dependent manner. RAW264.7 macrophages treated with iNOS inhibitor Aminoguanidine reverts the attenuation in arginase-blocked condition. Further, the NO block created by Salmonella was removed by increasing concentration of l-arginine. The whole-mice system arginase I, although constitutive, is much more abundant than the inducible arginase II isoform. Inhibition of arginase activity in mice during the course of Salmonella infection reduces the bacterial burden and delays the disease outcome in a NO dependent manner.     

Type I IFNs stimulate nitric oxide production and resistance to Trypanosoma cruzi infection

The participation of type I IFNs (IFN-I) in NO production and resistance to Trypanosoma cruzi infection was investigated. Adherent cells obtained from the peritoneal cavity of mice infected by the i.p. route produced NO and IFN-I. Synthesis of NO by these cells was partially inhibited by treatment with anti-IFN-alphabeta or anti-TNF-alpha Abs. Compared with susceptible BALB/c mice, peritoneal cells from parasite-infected resistant C57BL/6 mice produced more NO (2-fold), IFN-I (10-fold), and TNF-alpha (3.5-fold). Later in the infection, IFN-I levels measured in spleen cell (SC) cultures from 8-day infected mice were greater in C57BL/6 than in infected BALB/c mice, and treatment of the cultures with anti-IFN-alphabeta Ab reduced NO production. IFN-gamma or IL-10 production by SCs was not different between the two mouse strains; IL-4 was not detectable. Treatment of C57BL/6 mice with IFN-I reduced parasitemia levels in the acute phase of infection. Mice deprived of the IFN-alphabetaR gene developed 3-fold higher parasitemia levels in the acute phase in comparison with control 129Sv mice. Production of NO by peritoneal macrophages and SCs was reduced in mice that lacked signaling by IFN-alphabeta, whereas parasitism of macrophages was heavier than in control wild-type mice. We conclude that IFN-I costimulate NO synthesis early in T. cruzi infection, which contributes to a better control of the parasitemia in resistant mice.     

An effect of parasite-encoded arginase on the outcome of murine cutaneous leishmaniasis

Classical activation of macrophages infected with Leishmania species results in expression and activation of inducible NO synthase (iNOS) leading to intracellular parasite killing. Macrophages can contrastingly undergo alternative activation with increased arginase activity, metabolism of arginine along the polyamine pathway, and consequent parasite survival. An active role for parasite-encoded arginase in host microbicidal responses has not previously been documented. To test the hypothesis that parasite-encoded arginase can influence macrophage responses to intracellular Leishmania, a comparative genetic approach featuring arginase-deficient mutants of L. mexicana lacking both alleles of the gene encoding arginase (Deltaarg), as well as wild-type and complemented Deltaarg controls (Deltaarg[pArg]), was implemented. The studies showed: 1) the absence of parasite arginase resulted in a significantly attenuated infection of mice (p<0.05); 2) poorer survival of Deltaarg in mouse macrophages than controls correlated with greater NO generation; 3) the difference between Deltaarg or control intracellular survival was abrogated in iNOS-deficient macrophages, suggesting iNOS activity was responsible for increased Deltaarg killing; 4) consistently, immunohistochemistry showed enhanced nitrotyrosine modifications in tissues of mice infected with Deltaarg compared with control parasites. Furthermore, 5) in the face of decreased parasite survival, lymph node cells draining cutaneous lesions of Deltaarg parasites produced more IFN-gamma and less IL-4 and IL-10 than controls. These data intimate that parasite-encoded arginase of Leishmania mexicana subverts macrophage microbicidal activity by diverting arginine away from iNOS.     

Leishmania major: analysis of lymphocyte and macrophage cellular phenotypes during infection of susceptible and resistant mice

Genetically susceptible BALB/c and resistant C57BL/6 mice were infected with Leishmania major and the phenotypes of the responding cells in the draining lymph nodes and cutaneous lesions were analyzed. As early as 1 week, significantly increased numbers of L3T4+ cells as compared to Lyt-2+ cells were present in BALB/c mice lymph nodes (P less than 0.005). Increases in L3T4+ and Lyt-2+ cells were comparable in C57BL/6 mice, resulting in threefold lower L3T4/Lyt-2 ratio than in BALB/c mice. T cell subsets were activated in both strains to express interleukin-2 receptor (IL2R) above resting values, although greater numbers of activated L3T4+ cells were present in the draining lymph nodes from BALB/c at 1 and 3 weeks of infection than in C57BL/6 (P = 0.02). Despite the presence of activated L3T4+ cells in both strains, macrophages differed in the expression of immunologically important surface molecules during infection. Tissue macrophages from BALB/c mice were IgG1/G2b Fc receptor (FcR)+ and Ia- late in disease, whereas macrophages in C57BL/6 became FcR and Ia during healing. BALB/c mice, treated with monoclonal antibody GK1.5 to transiently deplete L3T4+ cells, became resistant to subsequent infection and developed a macrophage phenotype that was FcR- and Ia+. These differences in macrophage phenotype were closely linked to susceptibility during infection with L. major and may play a role in the pathophysiology of murine leishmaniasis.     

The impaired pregnancy outcome in murine congenital toxoplasmosis is associated with a pro-inflammatory immune response, but not correlated with decidual inducible nitric oxide synthase expression

Congenital toxoplasmosis is associated with adverse pregnancy outcome. Despite the type 1 immune response, C57BL/6 mice are more susceptible than BALB/c mice to Toxoplasma gondii infection. Additionally, successful pregnancy appears to be correlated with type 2 T helper maternal immunity and regulatory T cells. In order to investigate the mechanisms of susceptibility/resistance to congenital toxoplasmosis in mice with different genetic backgrounds and the influence of inducible nitric oxide synthase in pregnancy outcome, groups of C57BL/6, BALB/c and C57BL/6 iNOS(-/-) females were orally infected with T. gondii ME-49 strain on day 1 of pregnancy and were sacrificed on day 8 p.i. and day 19 p.i. The uterus and placenta were evaluated for the foetal resorption rate, parasite load, immunological and histological changes. C57BL/6 mice presented inflammatory foci in the decidua (endometrium) of the uterus at a higher frequency than BALB/c mice on day 8 p.i., and a large number of pregnant C57BL/6 mice presented necrotic implantation sites. The parasite was seldom found in the uterus or placenta of either lineage of mice. Interestingly, there was no observed difference in inducible nitric oxide synthase expression in the uterus and placenta of infected mice. In addition, higher levels of TNF-α were detected in serum samples from C57BL/6 mice compared with BALB/c mice. Accordingly, C57BL/6 mice presented with levels of 90% abortion compared with 50% in BALB/c mice on day 19 p.i. C57BL/6 iNOS(-/-) mice showed low placental parasite counts and high absorption rates, similar to wild type mice. The data suggest that the impaired pregnancy outcome due to T. gondii infection in C57BL/6 mice could be associated with a higher inflammatory response leading to cell apoptosis and necrosis of implantation sites compared with BALB/c mice, and this phenomenon was not due to inducible nitric oxide synthase expression in the decidua.     

A novel B-2 suppressor cell regulating susceptibility/resistance of mice to Toxoplasma gondii infection

Irradiation treatment enhanced resistance of C57BL/6, but not BALB/c against Toxoplasma gondii infection. Six Gy-irradiated (IR) C57BL/6 recipients of B-2 cells from T. gondii-infected C57BL/6 died after infection. B-2 suppressor cells from infected C57BL/6 enhanced production of IL-4 and IL-10 in peritoneal exudate cells (PECs), and down-regulated NO release in peritoneal macrophages after infection. On the other hand, B-2 suppressor cells were not detected in a strain, BALB/c, resistant against infection. These data indicated that irradiation-sensitive B-2 cells regulated susceptibility/resistance in mice against T. gondii infection.     

Trypanosoma brucei: influence of host strain and parasite antigenic type on infections in mice

Inbred mice were infected with cloned populations of Trypanosoma brucei brucei Lister S42 under carefully controlled conditions. The course of infection was found to depend both on host strain and the antigenic type of the infecting organisms. The two antigenic types used, “NIM2” and “NIM6” had differing virulence for (CBA/H × C57BL/6)F₁ mice, and when mice were infected with parasites of one clone, trypanosomes of the other type frequently appeared after the initial population had been eliminated. Different mouse strains had varying susceptibility to clone NIM6. In most cases there was an inverse relation between the survival time and the parasite load during the first peak of parasitemia. The differences in resistance to T. brucei were unrelated to H-2 haplotype: C57BL/6 and (CBA/H × C57BL/6)F₁ were most resistant, CBA/H, BALB/c and DBA/2 less so, and C3H/He most susceptible.     

Induction of multiple chemokine and colony-stimulating factor genes in experimental Burkholderia pseudomallei infection

Melioidosis is a disease of the tropics caused by the facultative intracellular bacterium Burkholderia pseudomallei. In human infection, increased levels of IFN-gamma in addition to the chemokines interferon-gamma-inducible protein 10 (IP-10) and monocyte interferon-gamma-inducible protein (Mig) have been demonstrated. However, the role of these and other chemokines in the pathogenesis of melioidosis remains unknown. Using BALB/c and C57BL/6 mice as models of the acute and chronic forms of human melioidosis, the induction of mRNA was assessed for various chemokines and CSF (G-CSF, M-CSF, GM-CSF, IP-10, Mig, RANTES, MCP-1, KC and MIP-2) in spleen and liver following B. pseudomallei infection. Patterns of chemokine and CSF induction were similar in liver and spleen; however, responses were typically greater in spleen, which reflected higher tissue bacterial loads. In BALB/c mice, high-level expression of mRNA for all chemokines and CSF investigated was demonstrated at day 3 postinfection, correlating with peak bacterial load and extensive infiltration of leucocytes. In contrast, increased mRNA expression and bacterial numbers in C57BL/6 mice were greatest between 4 and 14 days following infection. This paralleled increases in the size and number of abscesses in liver and spleen of C57BL/6 mice at days 3 and 14 postinfection. Earlier induction of cytokine-induced neutrophil chemoattractant (KC), macrophage inflammatory protein-2 (MIP-2), monocyte chemoattractant protein-1 (MCP-1), granulocyte-macrophage CSF (GM-CSF) and macrophage CSF (M-CSF) mRNA was demonstrated in spleen, while MIP-2, MCP-1, IP-10 and Mig were demonstrated in liver of BALB/c mice when compared to spleen and liver of C57BL/6. The magnitude of cellular responses observed in the tissue correlated with increased levels of the chemokines and CSF investigated, as well as bacterial load. Compared with C57BL/6 mice, greater infiltration of neutrophils was observed in liver and spleen of BALB/c mice at day 3. In contrast, early lesions in C57BL/6 mice predominantly comprised macrophages. These results suggest that the inability of BALB/c mice to contain the infection at sites of inflammation may underlie the susceptible phenotype of this mouse strain towards B. pseudomallei infection.