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Periodontitis is a chronic inflammatory disease with a multifactorial etiology. We investigated whether human major histocompatibility complex (MHC) polymorphisms (6p21.3) are associated with periodontal parameters. Parogene 1 population samples ( n = 169) were analyzed with 13,245 single nucleotide polymorphisms (SNPs) of the MHC region. Eighteen selected SNPs ( P ≤ 0.001) were replicated in Parogene 2 population samples ( n = 339) and the Health 2000 Survey ( n = 1,420). All subjects had a detailed clinical and radiographic oral health examination. Serum lymphotoxin-α (LTA) concentrations were measured in the Parogene populations, and the protein was detected in inflamed periodontal tissue. In the Parogene 1 population, 10 SNPs were associated with periodontal parameters. The strongest associations emerged from the parameters bleeding on probing (BOP) and a probing pocket depth (PPD) of ≥6 mm with the genes BAT1 , NFKBIL1 , and LTA . Six SNPs, rs11796, rs3130059, rs2239527, rs2071591, rs909253, and rs1041981 ( r 2 , ≥0.92), constituted a risk haplotype. In the Parogene 1 population, the haplotype had the strongest association with the parameter BOP, a PPD of ≥6 mm, and severe periodontitis with odds ratios (95% confidence intervals) of 2.63 (2.21 to 3.20), 2.90 (2.37 to 3.52), and 3.10 (1.63 to 5.98), respectively. These results were replicated in the other two populations. High serum LTA concentrations in the Parogene population were associated with the periodontitis risk alleles of the LTA SNPs (rs909253 and rs1041981) of the haplotype. In addition, the protein was expressed in inflamed gingival connective tissue. We identified a novel BAT1-NFKBIL1-LTA haplotype as a significant contributor to the risk of periodontitis. The genetic polymorphisms in the MHC class III region may be functionally important in periodontitis susceptibility.

B cell responses are required for resistance to Toxoplasma gondii ; however, the events that lead to production of class-switched antibodies during T. gondii infection have not been defined. Indeed, mice challenged with the parasite exhibited an expansion of T follicular helper cells and germinal center B cells in the spleen. Unexpectedly, this was not associated with germinal center formation and was instead accompanied by profound changes in splenic organization. This phenomenon was transient and was correlated with a decrease in expression of effector proteins that contribute to splenic organization, including lymphotoxins α and β. The importance of lymphotoxin was confirmed, as the use of a lymphotoxin β receptor agonist results in partial restoration of splenic structure. Splenectomized mice were used to test the splenic contribution to the antibody response during T. gondii infection. Analysis of splenectomized mice revealed delayed kinetics in the production of parasite-specific antibody, but the mice did eventually develop normal levels of parasite-specific antibody. Together, these studies provide a better understanding of how infection with T. gondii impacts the customized structures required for the optimal humoral responses to the parasite and the role of lymphotoxin in these events.

To study the specific role of transmembrane tumor necrosis factor (tmTNF) in protective and pathological responses against the gastrointestinal helminth Trichinella spiralis , we compared the immune responses of TNF-α/lymphotoxin alpha (LTα) −/− mice expressing noncleavable transgenic tmTNF to those of TNF-α/LTα −/− and wild-type mice. The susceptibility of TNF-α/LTα −/− mice to T. spiralis infection was associated with impaired induction of a protective Th2 response and the lack of mucosal mastocytosis. Although tmTNF-expressing transgenic (tmTNF-tg) mice also had a reduced Th2 response, the mast cell response was greater than that observed in TNF-α/LTα −/− mice and was sufficient to induce the expulsion of the parasite. T. spiralis infection of tmTNF-tg mice resulted in significant intestinal pathology characterized by villus atrophy and crypt hyperplasia comparable to that induced following the infection of wild-type mice, while pathology in TNF-α/LTα −/− mice was significantly reduced. Our data thus indicate a role for tmTNF in host defense against gastrointestinal helminths and in the accompanying enteropathy. Furthermore, they also demonstrate that TNF-α is required for the induction of Th2 immune responses related to infection with gastrointestinal helminth parasites.

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

Tuberculosis is a chronic bacterial disease with a complex pathogenesis. An effective immunity against Mycobacterium tuberculosis requires both the innate and adaptive immune responses, including proper T helper (Th) type 1 cell function. FURIN is a proprotein convertase subtilisin/kexin (PCSK) enzyme, which is highly expressed in Th1 type cells. FURIN expression in T cells is essential for maintaining peripheral immune tolerance, but its role in the innate immunity and infections has remained elusive. Here, we utilized Mycobacterium marinum infection models in zebrafish ( Danio rerio ) to investigate how furin regulates host responses against mycobacteria. In steady-state furinA td204e/+ fish reduced furinA mRNA levels associated with low granulocyte counts and elevated Th cell transcription factor expressions. Silencing furin genes reduced the survival of M. marinum -infected zebrafish embryos. A mycobacterial infection upregulated furinA in adult zebrafish, and infected furinA td204e/+ mutants exhibited a proinflammatory phenotype characterized by elevated tumor necrosis factor a ( tnfa ), lymphotoxin alpha ( lta ) and interleukin 17a/f3 ( il17a/f3 ) expression levels. The enhanced innate immune response in the furinA td204e/+ mutants correlated with a significantly decreased bacterial burden in a chronic M. marinum infection model. Our data show that upregulated furinA expression can serve as a marker for mycobacterial disease, since it inhibits early host responses and consequently promotes bacterial growth in a chronic infection.

Although the essential role of tumor necrosis factor (TNF) in resistance toListeria monocytogenesinfection is well established, the roles of the related cytokines lymphotoxin alpha (LTα) and lymphotoxin beta (LTβ) are unknown. Using C57BL/6 mice in which the genes for these cytokines were disrupted, we examined the contributions of TNF, LTα, and LTβ in the host response toListeria. To overcome the lack of peripheral lymph nodes in LTα−/−and LTβ−/−mice, bone marrow chimeras were constructed. TNF−/−and LTα−/−chimeras that lacked both secreted LTα3and membrane-bound LTα1β2and LTα2β1were highly susceptible and succumbed 4.5 and 6 days, respectively, after a low-dose infection (200 CFU). LTβ−/−chimeras, which lacked only membrane-bound LT, controlled the infection in a manner comparable to wild-type (WT) chimeras. TheListeria-specific proliferative and gamma interferon T-cell responses were equivalent in all five groups of infected mice (LTα−/−and LTβ−/−chimeras, WT chimeras, and TNF−/−and WT mice). TNF−/−mice and LTα−/−chimeras, however, failed to generate the discrete foci of lymphocytes and macrophages that are essential for bacterial elimination. Rather, aberrant necrotic lesions comprised predominantly of neutrophils with relatively few lymphocytes and macrophages were observed in the livers and spleens of TNF−/−and LTα−/−chimeras. Therefore, in addition to TNF, soluble LTα3plays a separate essential role in control of listerial infection through control of leukocyte accumulation and organization in infected organs.

Listeria monocytogenesis an enteroinvasive intracellular bacterial pathogen that infects humans and other animals, including mice, sometimes resulting in severe systemic infections. Previous studies showed that intraperitoneal (i.p.) pretreatment of susceptible BALB/c mice with immune-stimulatory CpG DNA 48 to 96 h prior to i.p. challenge with virulentL. monocytogenesreduces bacterial numbers in livers by greater than 100-fold, correlating with recovery from infection. Here we show that oral pretreatment of BALB/c mice with CpG DNA results in decreased susceptibility to either oral or i.p. challenge withL. monocytogenes. A single dose of 200 μg of CpG DNA administered to BALB/c mice orally by gavage 48 h or 7 days before oral challenge with virulentL. monocytogenesreduces bacterial numbers approximately 10- to 100-fold in livers and spleens. Lymphotoxin alpha knockout mice lacking Peyer's patches (PPs) and pretreated orally with CpG DNA 48 h prior to oral challenge withL. monocytogenesalso have reduced susceptibility to infection, suggesting that PPs are required neither for oral infection nor for CpG-induced resistance against oral infection withL. monocytogenes. Surprisingly, 48-h oral pretreatment of BALB/c mice with 100 to 200 μg of CpG DNA results in approximately 100-fold-decreased bacterial numbers in livers following i.p. challenge withL. monocytogenes, suggesting, along with other data in this report, that orally delivered CpG DNA induces systemic resistance to infection. These results indicate that oral administration of CpG DNA induces systemic innate immune defenses against either oral or systemic infection with virulentL. monocytogenes.

Cytokines such as gamma interferon and tumor necrosis factor alpha (TNF-α) inhibit the intracellular replication of Chlamydia pneumoniae or Chlamydia trachomatis . In this study, we found that another cytokine, lymphotoxin (TNF-β), restricts the growth of C. pneumoniae in HEp-2 cells. When lymphotoxin (10 U/ml) was added during incubation from 8 to 16 h postinoculation, inclusion body formation was severely reduced. In addition, we observed activation of nitric oxide production and the nuclear transition of NF-κB in HEp-2 cells in response to lymphotoxin. These results suggest that inhibition of chlamydial growth by lymphotoxin is mediated, at least in part, by nuclear transition of NF-κB, resulting in induction of nitric oxide synthase to produce nitric oxide, a potent bacteristatic agent. This is the first report on antichlamydial activity of lymphotoxin through induction of nitric oxide.

Murine embryo fibroblasts (MEF) were found to secrete tumor necrosis factor (TNF) in response to stimulation with endotoxin. Endotoxin-induced TNF production by MEF was inhibited by cycloheximide. However, reversal of the effect of this inhibitor on protein synthesis results in TNF being secreted in amounts equivalent to those produced by endotoxin-induced MEF not treated with cycloheximide. Actinomycin D treatment of MEF blocked the production of endotoxin-induced TNF. Maximal production of TNF required MEF gene transcription during the first 6 h of incubation with endotoxin. To determine whether endotoxin-induced TNF alpha (TNF-alpha) and/or TNF beta were produced by MEF, cDNA was synthesized from the total RNA isolated from endotoxin-induced MEF and amplified by the polymerase chain reaction in the presence of oligonucleotide primers specific for each cytokine. On the basis of the polymerase chain reaction analysis, it was determined that TNF-alpha mRNA levels were increased in endotoxin-induced MEF. Thus, production of TNF-alpha by fibroblasts in response to the endotoxin component of bacterial cell walls is likely to contribute to the expression of TNF-mediated effects occurring in fibroblast-rich tissues infected with gram-negative bacteria.

Pseudomonas aeruginosa is a dominant pathogen in infection in cystic fibrosis. This bacterium is thought to play a major role in the chronic bronchial infection-induced pathophysiology. Our data showed that whole formalin-fixed heat-killed P. aeruginosa was mitogenic for human lymphocytes and induced production of substantial amounts of tumor necrosis factor alpha (TNF) in peripheral blood mononuclear leukocytes in cultures. Significant amounts of TNF were produced at 10(3) bacteria per 2 x 10(5) mononuclear leukocytes. Treatment of P. aeruginosa with polymixin B did not affect its ability to stimulate TNF production, suggesting that bacterial lipopolysaccharide is not involved. P. aeruginosa, however, did not stimulate production of the T-cell lymphokine lymphotoxin (TNF beta). Exotoxin A, considered to be an important virulence factor produced by P. aeruginosa, did not stimulate either lymphoproliferation or production of TNF. In fact, this toxin, at nontoxic concentrations, was found to depress lymphoproliferation induced by phytohemagglutinin and Staphylococcus aureus and decreased production of TNF, lymphotoxin, and gamma interferon in either lymphocytes or macrophages. This toxin similarly inhibited the production of interleukin-1 beta (IL-1 beta) and IL-1 alpha, but for the inhibition of the latter, 25-fold-less toxin was required than for inhibition of the former. Inhibition of production of TNF was as sensitive as the IL-1 alpha to exotoxin A. The effects of exotoxin A on lymphoproliferation and cytokine production could be neutralized by the addition of anti-exotoxin A antibodies. These results suggest that two mechanisms by which P. aeruginosa could contribute to the chronic bronchial infection-induced pathophysiology are the nonspecific stimulation of TNF and IL-1 and the release of exotoxin A, a toxin which depresses immune responses.

The immune system provides different mechanisms to protect organisms against pathogens, most of which are infectious agents. Simultaneously, immune activation secondary to genetic factors and/or environmental signals can induce detrimental autoimmunity. The effector pathways in host defense and autoimmunity use similar cytokines and chemokines. Accordingly, tumor necrosis factor alpha (TNF-α), for instance, is similarly important in the control of various infections and in the induction of autoimmunity. Hallmarks of the adaptive immune system are antigen-specific cellular and humoral immune responses. Secondary lymphoid organs serve as sites of contact between antigen-presenting cells (APCs) and immune effector T and B lymphocytes. Chemokines and cytokines serve as messengers determining the type of immune response to a given antigen. The TNF family cytokine lymphotoxin (LT) plays a pivotal role in the development of secondary lymphoid organs. The chronic and relapsing course of many autoimmune diseases calls for new biological agents capable of suppressing the underlying inflammatory disorders. Recent studies indicate that inhibition of LTβ receptor (LTβR)-mediated signaling in adult animals suppresses autoimmunity by modulating the cellular structure of secondary lymphoid organs (reviewed in reference 22). Because of the wide range of autoimmune diseases positively influenced by this treatment, blockade of the LTβR might serve as a new treatment principle for human autoimmune diseases. However, immune responses to infectious pathogens are also altered in mice with disrupted LTβR signaling. While the course of virus- and lipopolysaccharide (LPS)-induced shock, experimental Trypanosoma brucei infection, cerebral malaria, and experimental prion disease are less severe, inhibition of the LTβR is also associated with exacerbation of mycobacterial infection and infectious colitis. This review summarizes the findings of studies using mice with disrupted LTβR signaling in models of infectious diseases and discusses the relevance of these observations in considering LTβR blockade as a potential treatment for human autoimmune diseases.

Using a multiprobe RNase protection assay, we examined cytokine and chemokine mRNAs that were expressed after corneal infection with Pseudomonas aeruginosa in mice. Cytokines that were upregulated included interleukin-1α (IL-1α) and -1β, IL-1 receptor antagonist, IL-6, IL-11, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, macrophage colony-stimulating factor, stem cell factor, lymphotoxin β, transforming growth factor β1, and tumor necrosis factor alpha. Chemokine transcripts that were upregulated included Eotaxin; gamma-interferon-inducible protein 10; monocyte chemoattractant protein 1; macrophage inflammatory proteins 1α, 1β, and 2; and RANTES. Peak expression of these cytokines and chemokines was observed between 1 and 3 days after infection. These responses returned to or approached baseline preinfection levels by 7 days after ocular challenge. Identification of the various cytokines and chemokines upregulated during corneal infection provides important information relevant to unraveling the pathogenesis induced by this bacterium and provides hope that specific molecules can be targeted for therapy.

The 30-kDa secreted antigen of Mycobacterium tuberculosis was a strong inducer of tumor necrosis factor alpha in human monocytes. Our findings suggest that tumor necrosis factor alpha production may be up-regulated at both the posttranscriptional and transcriptional levels. Regulation at the posttranscriptional level probably reflects enhanced translational efficiency.

Peripheral blood leukocytes (PBL) of 41 subjects were tested for their ability to be stimulated by herpes simplex virus antigens as measured by [ 3 H]thymidine incorporation and lymphokine production (i.e., lymphocyte-derived chemotactic factor and lymphotoxin). The PBL of seronegative subjects failed to respond to viral antigens as measured by stimulation or lymphokine production. In contrast, PBL from seropositive subjects without clinical lesions of herpes labialis were stimulated by herpes simplex virus antigens and produced lymphokines. PBL from seropositive patients with clinical lesions of herpes labialis also produced lymphokines, but [ 3 H]thymidine incorporation was slightly depressed. These findings suggest that lymphocytes from patients with a recent herpes simplex virus infection may respond less vigorously to in vitro stimulation by herpes antigens, but our study fails to show any basic defect in the responsiveness of the lymphocytes to account for recurrent herpetic episodes.

The appearance of lymphotoxin in the culture fluid of phytohemagglutinin (PHA)-stimulated mouse spleen cells required two cell fractions that were separated by adherence to plastic. Upon stimulation with PHA, neither cell fraction alone produced significant amounts of lymphotoxin; however, when the cell fractions were combined and then stimulated with PHA, full activity was produced. Cytotoxic activity was not fully restored by combining PHA-stimulated cultured fluids from adherent and nonadherent cell fractions. This indicated that the cytotoxic activity was not the result of two factors, one produced by each cell fraction, that acted on the target cells, but rather, two cells interacted to produce lymphotoxin. Treatment of the unfractionated spleen cells with monoclonal anti-Thy1.2 and complement before PHA stimulation greatly reduced the production of lymphotoxin and indicated that at least one of the cells was a T cell. Lymphotoxin production was partially restored by the addition of nonadherent cells to the anti-Thy1.2-treated cells, suggesting that the T cell was nonadherent. Treatment of unfractionated cells with either silica or carrageenan had no effect on the subsequent production of lymphotoxin by PHA, suggesting that the adherent cell was not actively phagocytic.