Infection of mice lacking the common cytokine receptor gamma-chain (gamma(c)) reveals an unexpected role for CD4+ T lymphocytes in early IFN-gamma-dependent resistance to Toxoplasma gondii

Mice lacking the common cytokine receptor gamma-chain (gamma(c)) gene exhibit defective development of NK cells and CD8+ T cells and greatly diminished production of IFN-gamma. Because resistance of SCID mice to Toxoplasma gondii requires IL-12-dependent IFN-gamma production by NK cells, we expected that gamma(c)-deficient mice would succumb rapidly to the parasite. Surprisingly, however, most gamma(c)-deficient mice survived the acute phase of T. gondii infection. As in wild-type mice, this resistance required IL-12 and IFN-gamma; nevertheless, whereas wild-type mice depleted of CD4+ T cells survived, anti-CD4+ treated gamma(c)-deficient mice displayed diminished production of IFN-gamma and all succumbed to acute infection. These data not only reveal a role for CD4+ T lymphocytes in IFN-gamma-dependent host defense but also establish SCID and gamma(c)-deficient mice as powerful complementary tools for assessing the function of NK vs CD4+ T cells in immunopathophysiologic responses.

CD4+ T cell-mediated granulomatous pathology in schistosomiasis is downregulated by a B cell-dependent mechanism requiring Fc receptor signaling

The effector functions of CD4+ T lymphocytes are generally thought to be controlled by distinct populations of regulatory T cells and their soluble products. The role of B cells in the regulation of CD4-dependent host responses is less well understood. Hepatic egg granuloma formation and fibrosis in murine schistosomiasis are dependent on CD4+ lymphocytes, and previous studies have implicated CD8+ T cells or cross-regulatory cytokines produced by T helper (Th) lymphocytes as controlling elements of this pathologic process. In this report, we demonstrate that B cell-deficient (muMT) mice exposed to Schistosoma mansoni develop augmented tissue pathology and, more importantly, fail to undergo the spontaneous downmodulation in disease normally observed during late stages of infection. Unexpectedly, B cell deficiency did not significantly alter T cell proliferative response or cause a shift in the Th1/Th2 balance. Since schistosome-infected Fc receptor-deficient (FcR gamma chain knockout) mice display the same exacerbated egg pathology as that observed in infected muMT mice, the B cell- dependent regulatory mechanism revealed by these experiments appears to require receptor-mediated cell triggering. Together, the data demonstrate that humoral immune response/FcR interactions can play a major role in negatively controlling inflammatory disease induced by CD4+ T cells.

Decreased resistance of TNF receptor p55- and p75-deficient mice to chronic toxoplasmosis despite normal activation of inducible nitric oxide synthase in vivo

The importance of TNF-alpha in host defense to the intracellular parasite, Toxoplasma gondii, was investigated in mice lacking both the p55 and p75 receptors for this cytokine. Upon i.p. infection with the avirulent ME49 strain, knockout mice were capable of limiting acute i.p. infection, but succumbed within 3 to 4 wk to a fulminant necrotizing encephalitis. Receptor-deficient mice harbored higher cyst burdens and exhibited uncontrolled tachyzoite replication in the brain. The lack of TNF receptors did not adversely affect the development of a type 1 IFN-gamma response. In vitro studies with peritoneal macrophages stimulated with IFN-gamma and tachyzoites indicated that under limiting concentrations of IFN-gamma, nitric oxide-mediated toxoplasmastatic activity is TNF-alpha dependent. However, this requirement is overcome by increasing the dose of IFN-gamma. Furthermore, both ex vivo and in vivo studies demonstrated that inducible nitric oxide synthase induction in the peritoneal cavity and brain is unimpaired in receptor-deficient mice. Thus, TNF-dependent immune control of T. gondii expansion in the brain involves an effector function distinct from inducible nitric oxide synthase activation.

Cytokines as determinants of disease and disease interactions

The immune response to pathogens results in both host resistance and immunopathology. Cytokines and in particular those lymphokines produced by Th1 and Th2 cells play a key role in determining the balance between these two immunologic outcomes. Recent data suggest that interleukin-10, a product of both Th2 cells and macrophages, protects the host against excessive immunopathology. The cytokine environment generated by different pathogens may also influence the course and outcome of infections with unrelated organisms. This relationship may be particularly important in the case of HIV-1 where prior Th1 or Th2 biases established by helminth or intracellular infections may influence either initial viral susceptibility or drive progression to AIDS through immune activation.

In vivo microbial stimulation induces rapid CD40 ligand-independent production of interleukin 12 by dendritic cells and their redistribution to T cell areas

The early induction of interleukin (IL)-12 is a critical event in determining the development of both innate resistance and adaptive immunity to many intracellular pathogens. Previous in vitro studies have suggested that the macrophage (MPhi) is a major source of the initial IL-12 produced upon microbial stimulation and that this response promotes the differentiation of protective T helper cell 1 (Th1) CD4+ lymphocytes from precursors that are primed on antigen-bearing dendritic cells (DC). Here, we demonstrate by immunolocalization experiments and flow cytometric analysis that, contrary to expectation, DC and not MPhi are the initial cells to synthesize IL-12 in the spleens of mice exposed in vivo to an extract of Toxoplasma gondii or to lipopolysaccharide, two well characterized microbial stimulants of the cytokine. Importantly, this production of IL-12 occurs very rapidly and is independent of interferon gamma priming or of signals from T cells, such as CD40 ligand. IL-12 production by splenic DC is accompanied by an increase in number of DCs, as well as a redistribution to the T cell areas and the acquisition of markers characteristic of interdigitating dendritic cells. The capacity of splenic DC but not MPhi to synthesize de novo high levels of IL-12 within hours of exposure to microbial products in vivo, as well as the ability of the same stimuli to induce migration of DC to the T cell areas, argues that DC function simultaneously as both antigen-presenting cells and IL-12 producing accessory cells in the initiation of cell-mediated immunity to intracellular pathogens. This model avoids the need to invoke a three-cell interaction for Th1 differentiation and points to the DC as both a sentinel for innate recognition and the dictator of class selection in the subsequent adaptive response.

Analysis of granuloma formation in double cytokine-deficient mice reveals a central role for IL-10 in polarizing both T helper cell 1- and T helper cell 2-type cytokine responses in vivo

In response to i.v.-injected eggs of Schistosoma mansoni, normal mice develop a dominant type 2 response, whereas IL-10-deficient animals generate a mixed type 1/type 2 cytokine profile and show reduced pulmonary granuloma formation. IL-4-deficient mice, while displaying diminished type 2 responses and granulomatous inflammation, also do not fully default to a type 1 cytokine profile. Strikingly, mice doubly deficient in IL-4 and IL-10 are completely defective in pulmonary granuloma formation and develop a highly polarized type 1 cytokine pattern. In analogous fashion, mice deficient in both IL-12 and IL-10 generate highly exacerbated type 2 cytokine responses, whereas in wild-type animals, IL-12 depletion minimally effects egg-induced cytokine production. Together, these results argue first that IL-10 is an important endogenous down-regulator of type 2 as well as type 1 cytokine synthesis, and second, that its induction is critical for type 2 response polarization in vivo.

Analysis of granuloma formation in double cytokine-deficient mice reveals a central role for IL-10 in polarizing both T helper cell 1- and T helper cell 2-type cytokine responses in vivo

In response to i.v.-injected eggs of Schistosoma mansoni, normal mice develop a dominant type 2 response, whereas IL-10-deficient animals generate a mixed type 1/type 2 cytokine profile and show reduced pulmonary granuloma formation. IL-4-deficient mice, while displaying diminished type 2 responses and granulomatous inflammation, also do not fully default to a type 1 cytokine profile. Strikingly, mice doubly deficient in IL-4 and IL-10 are completely defective in pulmonary granuloma formation and develop a highly polarized type 1 cytokine pattern. In analogous fashion, mice deficient in both IL-12 and IL-10 generate highly exacerbated type 2 cytokine responses, whereas in wild-type animals, IL-12 depletion minimally effects egg-induced cytokine production. Together, these results argue first that IL-10 is an important endogenous down-regulator of type 2 as well as type 1 cytokine synthesis, and second, that its induction is critical for type 2 response polarization in vivo.

Interferon consensus sequence binding protein-deficient mice display impaired resistance to intracellular infection due to a primary defect in interleukin 12 p40 induction

Mice lacking the transcription factor interferon consensus sequence binding protein (ICSBP), a member of the interferon regulatory factor family of transcription proteins, were infected with the intracellular protozoan, Toxoplasma gondii. ICSBP-deficient mice exhibited unchecked parasite replication in vivo and rapidly succumbed within 14 d after inoculation with an avirulent Toxoplasma strain. In contrast, few intracellular parasites were observed in wild-type littermates and these animals survived for at least 60 d after infection. Analysis of cytokine synthesis in vitro and in vivo revealed a major deficiency in the expression of both interferon (IFN)-gamma and interleukin (IL)-12 p40 in the T. gondii exposed ICSBP-/- animals. In related experiments, macrophages from uninfected ICSBP-/- mice were shown to display a selective impairment in the mRNA expression of IL-12 p40 but not IL-1alpha, IL-1beta, IL-1Ra, IL-6, IL-10, or TNF-alpha in response to live parasites, parasite antigen, lipopolysaccharide, or Staphylococcus aureus. This selective defect in IL-12 p40 production was observed regardless of whether the macrophages had been primed with IFN-gamma. We hypothesize that the impaired synthesis of IL-12 p40 in ICSBP-/- animals is the primary lesion responsible for the loss in resistance to T. gondii because IFN-gamma-induced parasite killing was unimpaired in vitro and, more importantly, administration of exogenous IL-12 in vivo significantly prolonged survival of the infected mice. Together these findings implicate ICSBP as a major transcription factor which directly or indirectly regulates IL-12 p40 gene activation and, as a consequence, IFN-gamma-dependent host resistance.

Mechanisms of innate resistance to Toxoplasma gondii infection

The interaction of protozoan parasites with innate host defences is critical in determining the character of the subsequent infection. The initial steps in the encounter of Toxoplasma gondii with the vertebrate immune system provide a striking example of this important aspect of the host-parasite relationship. In immuno-competent individuals this intracellular protozoan produces an asymptomatic chronic infection as part of its strategy for transmission. Nevertheless, T. gondii is inherently a highly virulent pathogen. The rapid induction by the parasite of a potent cell-mediated immune response that both limits its growth and drives conversion to a dormant cyst stage explains this apparent paradox. Studies with gene-deficient mice have demonstrated the interleukin-12 (IL-12)-dependent production of interferon gamma (IFN-gamma) to be of paramount importance in controlling early parasite growth. However, this seems to be independent of nitric oxide production as mice deficient in inducible nitric oxide synthase (iNOS) and tumour necrosis factor receptor were able to control early growth of T. gondii, although, they later succumbed to infection. Nitric oxide does, however, seem to be important in controlling persistent infection; treating chronic infection with iNOS metabolic inhibitors results in disease reactivation. Preliminary evidence implicates neutrophils in effector pathways against this parasite distinct from that described for macrophages. Once initiated, IL-12-dependent IFN-gamma production in synergy with other proinflammatory cytokines can positively feed back on itself to induce 'cytokine shock'. Regulatory cytokines, particularly IL-10, are essential to down-regulate inflammation and limit host pathology.

Adsorption to aluminum hydroxide promotes the activity of IL-12 as an adjuvant for antibody as well as type 1 cytokine responses to HIV-1 gp120

A series of protocols were tested to examine the adjuvant effects of IL-12 on humoral and type 1 cytokine responses elicited in mice by recombinant gp120 envelope protein from HIV-1. This Ag fails to induce detectable Ab responses when administered s.c. alone, but stimulates low Ab levels when combined with aluminum hydroxide (alum). Moreover, when i.p. injected rIL-12 was included in the immunization, no increase in Ab production was observed. Importantly, optimal gp120 Ab responses were achieved by immunizing mice s.c. with gp120 and rIL-12 simultaneously coadsorbed to alum. These animals displayed a highly polarized, type 1 cytokine profile, with the emergence of anti-gp120 Ig belonging to the IgG2 and IgG3 isotypes. In addition, a major increase occurred in Ab of the IgG1 subclass. The superior adjuvant activity of alum-adsorbed IL-12 compared with that of the free cytokine correlated with the prolonged detection of IFN-gamma in the sera of animals immunized using the former procedure. In related experiments, in vitro neutralization of IL-12 was shown to inhibit IFN-gamma production by spleen cells from mice immunized with gp120 plus alum, but not by splenocytes from mice primed in the presence of IL-12, suggesting that the latter protocol induces a stable type 1 phenotype. These studies demonstrate that presentation of IL-12 on alum enhances its immunomodulatory effects and establish a protocol for the use of the cytokine as an adjuvant for simultaneously promoting both humoral Ab and type 1 cytokine responses.

Change of foot size with weightbearing. A study of 2829 children 3 to 18 years of age

The change of foot length and width with age has been reported in a few anthropometric studies in the literature. However, the relationship with body height rarely is reported, and the dynamic effect of weightbearing on foot size has not been documented. In this series, 2829 children 3 to 18 years of age of equal gender distribution were included in the study. The foot length and width on weightbearing and nonweightbearing were measured with a special precision electronic caliper. The foot length and width were found to increase linearly from the age of 3 years until 12 years in girls and 15 years in boys. This was followed by a phase during which the increase plateaued. The foot length and width increased significantly on weightbearing at all ages in both genders with a mean of 2.1 to 4.4 mm or 3.1% to 4.8%, respectively. The foot length and width also were found to correlate significantly with the body height in both genders, with a correlation coefficient of 0.96 to 0.98. No significant differences were found between the sizes of the dominant and nondominant foot in either gender.

Adsorption to aluminum hydroxide promotes the activity of IL-12 as an adjuvant for antibody as well as type 1 cytokine responses to HIV-1 gp120

A series of protocols were tested to examine the adjuvant effects of IL-12 on humoral and type 1 cytokine responses elicited in mice by recombinant gp120 envelope protein from HIV-1. This Ag fails to induce detectable Ab responses when administered s.c. alone, but stimulates low Ab levels when combined with aluminum hydroxide (alum). Moreover, when i.p. injected rIL-12 was included in the immunization, no increase in Ab production was observed. Importantly, optimal gp120 Ab responses were achieved by immunizing mice s.c. with gp120 and rIL-12 simultaneously coadsorbed to alum. These animals displayed a highly polarized, type 1 cytokine profile, with the emergence of anti-gp120 Ig belonging to the IgG2 and IgG3 isotypes. In addition, a major increase occurred in Ab of the IgG1 subclass. The superior adjuvant activity of alum-adsorbed IL-12 compared with that of the free cytokine correlated with the prolonged detection of IFN-gamma in the sera of animals immunized using the former procedure. In related experiments, in vitro neutralization of IL-12 was shown to inhibit IFN-gamma production by spleen cells from mice immunized with gp120 plus alum, but not by splenocytes from mice primed in the presence of IL-12, suggesting that the latter protocol induces a stable type 1 phenotype. These studies demonstrate that presentation of IL-12 on alum enhances its immunomodulatory effects and establish a protocol for the use of the cytokine as an adjuvant for simultaneously promoting both humoral Ab and type 1 cytokine responses.

Fc epsilonRI-deficient mice infected with Schistosoma mansoni mount normal Th2-type responses while displaying enhanced liver pathology

The IgE/Fc epsilonRI interaction is postulated to play an important role in resistance to helminths both at the level of anti-parasitic effector cell function and in the initiation of Th2 responses through IL-4 produced by Fc epsilonRI+ non-B, non-T (NBNT) cells. To formally evaluate the role of IgE/Fc epsilonRI signaling in the host response to helminths we studied Schistosoma mansoni infection in Fc epsilonRI knockout (KO) mice. Infected wild-type (wt) and KO animals showed comparable adult worm and tissue egg burdens, arguing against a role for Fc epsilonRI interactions in host resistance. Significantly, NBNT cells from infected KO, in contrast to wt animals, did not secrete IL-4 when stimulated with anti-IgE Ab or soluble parasite Ag. Nevertheless, serum IgE levels and Th2 cytokine production profiles were comparable in both strains of mice, demonstrating that the Ag-dependent stimulation of IL-4 secretion by NBNT cells is not essential for helminth-induced Th2 differentiation. However, when stimulated with low Ag doses, splenocytes from infected Fc epsilonRI-deficient mice produced less IL-4 in vitro than similar cultures from infected wt animals, an effect attributable to their defective NBNT cell function. Moreover, infected KO mice showed enhanced egg granuloma formation and hepatic fibrosis, revealing that the IgE/Fc epsilonRI interaction, while not essential for Th2 response development or resistance to primary infection, plays a significant role in down-regulating host pathology.

Perforin-mediated cytolysis plays a limited role in host resistance to Toxoplasma gondii

Resistance of perforin knockout (PKO) mice to infection with Toxoplasma gondii was assessed in models of acute infection and during chronic disease. PKO mice vaccinated with the attenuated mutant, ts-4, displayed severely defective CTL responses against tachyzoite-infected targets. Lysis of the NK target, YAC-1, was also severely impaired in PKO mice following ts-4 vaccination. In contrast, wild-type mice developed high levels of CTL and NK lytic activity after ts-4 vaccination. Despite severely defective lytic activity, vaccinated PKO animals were completely resistant to challenge with the virulent strain RH, which normally causes a lethal acute infection. Resistance was attributable to production of IFN-gamma, which remained unimpaired in the PKO animals. In contrast, when PKO mice were infected with low virulence parasite strain ME49, which progresses to the cyst-forming stage after passage through an acute phase, accelerated mortality was observed beginning at 75 days postinfection. A three- to fourfold increase in brain cyst numbers was also found by day 30 in infected PKO animals. Nevertheless, the PKO strain produced normal levels of IFN-gamma after ME49 infection, ruling out impaired production of the latter cytokine as a cause of increased susceptibility. Together, these results show that perforin-dependent cytolytic function is not required for host resistance to lethal acute infection in preimmunized animals, but that the latter activity contributes to the control of infection during the chronic stage.

Fc epsilonRI-deficient mice infected with Schistosoma mansoni mount normal Th2-type responses while displaying enhanced liver pathology

The IgE/Fc epsilonRI interaction is postulated to play an important role in resistance to helminths both at the level of anti-parasitic effector cell function and in the initiation of Th2 responses through IL-4 produced by Fc epsilonRI+ non-B, non-T (NBNT) cells. To formally evaluate the role of IgE/Fc epsilonRI signaling in the host response to helminths we studied Schistosoma mansoni infection in Fc epsilonRI knockout (KO) mice. Infected wild-type (wt) and KO animals showed comparable adult worm and tissue egg burdens, arguing against a role for Fc epsilonRI interactions in host resistance. Significantly, NBNT cells from infected KO, in contrast to wt animals, did not secrete IL-4 when stimulated with anti-IgE Ab or soluble parasite Ag. Nevertheless, serum IgE levels and Th2 cytokine production profiles were comparable in both strains of mice, demonstrating that the Ag-dependent stimulation of IL-4 secretion by NBNT cells is not essential for helminth-induced Th2 differentiation. However, when stimulated with low Ag doses, splenocytes from infected Fc epsilonRI-deficient mice produced less IL-4 in vitro than similar cultures from infected wt animals, an effect attributable to their defective NBNT cell function. Moreover, infected KO mice showed enhanced egg granuloma formation and hepatic fibrosis, revealing that the IgE/Fc epsilonRI interaction, while not essential for Th2 response development or resistance to primary infection, plays a significant role in down-regulating host pathology.

Perforin-mediated cytolysis plays a limited role in host resistance to Toxoplasma gondii

Resistance of perforin knockout (PKO) mice to infection with Toxoplasma gondii was assessed in models of acute infection and during chronic disease. PKO mice vaccinated with the attenuated mutant, ts-4, displayed severely defective CTL responses against tachyzoite-infected targets. Lysis of the NK target, YAC-1, was also severely impaired in PKO mice following ts-4 vaccination. In contrast, wild-type mice developed high levels of CTL and NK lytic activity after ts-4 vaccination. Despite severely defective lytic activity, vaccinated PKO animals were completely resistant to challenge with the virulent strain RH, which normally causes a lethal acute infection. Resistance was attributable to production of IFN-gamma, which remained unimpaired in the PKO animals. In contrast, when PKO mice were infected with low virulence parasite strain ME49, which progresses to the cyst-forming stage after passage through an acute phase, accelerated mortality was observed beginning at 75 days postinfection. A three- to fourfold increase in brain cyst numbers was also found by day 30 in infected PKO animals. Nevertheless, the PKO strain produced normal levels of IFN-gamma after ME49 infection, ruling out impaired production of the latter cytokine as a cause of increased susceptibility. Together, these results show that perforin-dependent cytolytic function is not required for host resistance to lethal acute infection in preimmunized animals, but that the latter activity contributes to the control of infection during the chronic stage.

Unimpaired down-modulation of the hepatic granulomatous response in CD8 T-cell- and gamma interferon-deficient mice chronically infected with Schistosoma mansoni

The granulomatous response to schistosome eggs is a CD4 T-cell-dependent, Th2-cytokine-dominated immunopathologic response. As infection proceeds to chronicity, both granuloma formation and egg-induced cytokine production become downregulated, and previous experiments have implicated CD8 T cells in this process. One mechanism by which CD8 T cells could suppress immunopathology is through the production of the counterregulatory cytokine gamma interferon (IFN-gamma), but no in vivo evidence exists to directly support this hypothesis. In this study, we analyzed hepatic granuloma formation and egg-induced cytokine production in Schistosoma mansoni-infected gene knockout mice deficient in either CD8 lymphocytes or IFN-gamma. Surprisingly, we found that neither immunologic component plays an essential function in the control of granuloma and cytokine responses during either the acute or chronic stage of infection. Thus, other mechanisms may be more important in the regulation of immunopathology in schistosomiasis.

Dual-energy X-ray absorptiometry predicts bone formation in lower limb callotasis lengthening

The rate of regenerate bone mineral content (BMC) acceleration was studied using dual-energy X-ray absorptiometry (DEXA) in callotasis lengthening of the lower limb. Eleven youngsters (age range 5-17 years) undergoing callotasis lengthening for congenital, post-traumatic or post-infective conditions were studied longitudinally. Patients were initially scanned once a week until completion of the lengthening phase, and at 2-week intervals thereafter until removal of the fixator. They were subsequently followed up at regular intervals on an outpatient basis for up to 2 years after removal of the fixator (average, 14 months). The BMC accretion slopes exhibited by the patients and the rate of new bone formation allowed the identification of three groups. In the fast formation group, the rate of new bone formation was 0.3-0.6% per day. In the moderate formation group the rate of new bone formation is 0.1-0.3% per day, while in the poor formation group the rate of new bone formation is < 0.1% per day. From the analysis of time graphs, a direct correlation emerged between early bone formation and subsequent bone mineral content accretion. Measurement of BMC during callotasis lengthening in the lower limb allows precise monitoring of the process. It may prove useful to prevent complications occurring after removal of the fixator at an unduly early stage, such as plastic deformation and fracture through the regenerate bone. It may be used to predict the bone formation rate in a given patient, and to implement measures to try to influence it.

The indications for polysomnography and related procedures

This paper is a review of the literature on the use of polysomnography in the diagnosis of sleep disorders in the adult. It is based on a search of MEDLINE from January 1966 through April 1996. It has been reviewed and approved by the Board of Directors of the American Sleep Disorders Association and provides the background for the accompanying ASDA Standards of Practice Committee's Parameters for the Practice of Sleep Medicine in North America. The diagnostic categories reviewed are: sleep-related breathing disorders; other respiratory disorders; narcolepsy; parasomnias and sleep-related epilepsy; restless legs syndrome and periodic limb movement disorders: insomnia; and circadian rhythm sleep disorders. Where appropriate, previously published practice parameters papers are cited and discussed. The relevant published peer-reviewed literature used as the basis for critical decisions was compiled into accompanying evidence tables and is analyzed in the text. In the section on the assessment of sleep apnea syndrome, options for estimating pretest probability to select high risk patients are also reviewed. Sleep-testing procedures other than standard polysomnography are also addressed (daytime polysomnography, split-night studies, oximetry, limited full respiratory recordings, and less-than-full respiratory recording) and treatment-related follow-up studies are discussed.

Defects in cell-mediated immunity affect chronic, but not innate, resistance of mice to Mycobacterium avium infection

To investigate the role of cell-mediated immunity in the control of Mycobacterium avium infection, we studied the effects of targeted gene disruptions in components of the T lymphocyte-dependent, macrophage-mediated response on resistance of mice to this pathogen. Normal mice developed a chronic, asymptomatic infection, with rapid induction of mRNAs for IFN-gamma, IL-12, and TNF-alpha in spleen, liver, and lung. Bacterial loads in gene knockout, scid, and wild-type mice were indistinguishable for the first 4 wk of infection. However, by 8 wk postinfection, scid mice as well as animals with a targeted disruption of the IFN-gamma gene showed enhanced bacterial growth compared with wild-type controls. In contrast, knockout mice lacking the genes for the TNF-alpha p55/p75 receptors or inducible nitric oxide synthase not only developed comparable bacterial loads to wild-type animals, they also failed to display the splenomegaly and profound suppression of mitogen-induced lymphocyte proliferative responses evident in infected wild-type controls. Thus, M. avium is clearly distinct from other intracellular pathogens (e.g., Leishmania monocytogenes, Toxoplasma gondii, and Mycobacterium tuberculosis) whose initial replication in the host is tightly controlled by Th1-dependent effector mechanisms. Instead, the major effect of host cell-mediated immunity is to limit bacterial growth during the chronic phase of infection. Surprisingly, inducible nitric oxide appears to be more important for the immunopathology than for the host resistance induced by this bacterial pathogen.

Defects in cell-mediated immunity affect chronic, but not innate, resistance of mice to Mycobacterium avium infection

To investigate the role of cell-mediated immunity in the control of Mycobacterium avium infection, we studied the effects of targeted gene disruptions in components of the T lymphocyte-dependent, macrophage-mediated response on resistance of mice to this pathogen. Normal mice developed a chronic, asymptomatic infection, with rapid induction of mRNAs for IFN-gamma, IL-12, and TNF-alpha in spleen, liver, and lung. Bacterial loads in gene knockout, scid, and wild-type mice were indistinguishable for the first 4 wk of infection. However, by 8 wk postinfection, scid mice as well as animals with a targeted disruption of the IFN-gamma gene showed enhanced bacterial growth compared with wild-type controls. In contrast, knockout mice lacking the genes for the TNF-alpha p55/p75 receptors or inducible nitric oxide synthase not only developed comparable bacterial loads to wild-type animals, they also failed to display the splenomegaly and profound suppression of mitogen-induced lymphocyte proliferative responses evident in infected wild-type controls. Thus, M. avium is clearly distinct from other intracellular pathogens (e.g., Leishmania monocytogenes, Toxoplasma gondii, and Mycobacterium tuberculosis) whose initial replication in the host is tightly controlled by Th1-dependent effector mechanisms. Instead, the major effect of host cell-mediated immunity is to limit bacterial growth during the chronic phase of infection. Surprisingly, inducible nitric oxide appears to be more important for the immunopathology than for the host resistance induced by this bacterial pathogen.

Cytokine regulation of schistosome-induced granuloma and fibrosis

Schistosomiasis mansoni, a major cause of hepatic fibrosis in many developing countries, triggers a granulomatous inflammatory reaction in response to its eggs that lodge in the liver. The egg antigens are eliminated slowly, and the persistent granulomatous response leads to prolonged matrix synthesis and hepatic fibrosis. In mice, soluble egg antigens (SEA) induce interleukin 4 synthesis, promoting a dominant T helper type 2 lymphocyte accumulation with the release of additional cytokines (IL-5, IL-10), which not only suppress Th1 lymphocyte subset cytokines, but mediate the characteristic pathophysiology. Manipulation of the cytokine profile with antagonists or exogenous cytokine delivery alters the course of the hepatic inflammation and fibrosis. In the evolution of the granulomatous response to the S. mansoni eggs, transforming growth factor beta (TGF-beta) is also produced that may modulate inflammation and regulate fibrogenesis. In TGF-beta 1-gene targeted mutant mice that over-express TGF-beta 1 (TGF-beta 1 transgenics) or in which TGF-beta 1 has been inactivated (TGF-beta 1-/-; null mutation) or partially inactivated (TGF-beta 1+/-; null mutation heterozygotes), the altered production of TGF-beta 1 impacts on S. mansoni granuloma and hepatic fibrosis. In addition to the Th1/Th2 cytokine balance, modulation of TGF-beta 1 may change the outcome of chronic inflammatory fibrotic disease.

Inducible nitric oxide is essential for host control of persistent but not acute infection with the intracellular pathogen Toxoplasma gondii

The induction by IFN-gamma of reactive nitrogen intermediates has been postulated as a major mechanism of host resistance to intracellular pathogens. To formally test this hypothesis in vivo, the course of Toxoplasma gondii infection was assessed in nitric oxide synthase (iNOS)-/- mice. As expected, macrophages from these animals displayed defective microbicidal activity against the parasite in vitro. Nevertheless, in contrast to IFN-gamma-/- or IL-12 p40-/- animals, iNOS-deficient mice survived acute infection and controlled parasite growth at the site of inoculation. This early resistance was ablated by neutralization of IFN-gamma or IL-12 in vivo and markedly diminished by depletion of neutrophils, demonstrating the existence of previously unappreciated NO independent mechanisms operating against the parasite during early infection. By 3-4 wk post infection, however, iNOS knockout mice did succumb to T. gondii. At that stage parasite expansion and pathology were evident in the central nervous system but not the periphery suggesting that the protective role of nitric oxide against this intracellular infection is tissue specific rather than systemic.