The novel lipopolysaccharide-binding protein CRISPLD2 is a critical serum protein to regulate endotoxin function.

LPS is an immunostimulatory component of Gram-negative bacteria. Acting on the immune system in a systemic fashion, LPS exposes the body to the hazard of septic shock. In this study we report that cysteine-rich secretory protein LCCL domain containing 2 (CRISPLD2/Crispld2; human and mouse/rat versions, respectively), expressed by multitissues and leukocytes, is a novel LPS-binding protein. As a serum protein, median CRISPLD2 concentrations in health volunteers and umbilical cord blood samples are 607 microg/ml and 290 microg/ml, respectively. Human peripheral blood granulocytes and mononuclear cells including monocytes, NK cells, and T cells spontaneously release CRISPLD2 (range, 0.2-0.9 microg/ml) and enhance CRISPLD2 secretion (range, 1.5-4.2 microg/ml) in response to stimulation of both LPS and humanized anti-human TLR4-IgA Ab in vitro. CRISPLD2 exhibits significant LPS binding affinity similar to that of soluble CD14, prevents LPS binding to target cells, reduces LPS-induced TNF-alpha and IL-6 production, and protects mice against endotoxin shock. In in vivo experiments, serum Crispld2 concentrations increased in response to a nontoxic dose of LPS and correlated negatively with LPS lethality, suggesting that CRISPLD2 serum concentrations not only are indicators of the degree of a body's exposure to LPS but also reflect an individual's LPS sensitivity.

Diminished response to interleukin-10 and reduced antibody-dependent cellular cytotoxicity of cord blood monocyte-derived macrophages.

Monocyte-derived macrophage (MPhi) subsets are generated by antagonistic induction pathways. A helper MPhi-type (Mh-MPhi) is induced by interferon gamma (IFN-gamma), whereas a cytotoxic MPhi-type (Mc-MPhi), induced by interleukin-10 (IL-10), is a potent mediator of antibody-dependent cellular cytotoxicity (ADCC). Compared with MPhi from healthy adults [peripheral blood monocyte-derived macrophages (PBMPhi)], cord blood MPhi (CBMPhi) were found less capable of generating Mh-MPhi. Here we tested the hypothesis that their generation of Mc-MPhi via IL-10 is also impaired. MPhi surface markers were phenotyped. IL-10 protein and mRNA production were detected after stimulation [alphaCD3 monoclonal antibody (mAb)]. CBMPhi or PBMPhi were co-cultured with MPhi-depleted mononuclear cells of adults and CD4-targeting antibodies as models for ADCC were added. In cord blood, we found diminished alphaCD3-induced IL-10 protein and mRNA production (p < 0.05 versus adults). Basal CD16 and HLA-DR expressions on CBMPhi of preterm and full-term neonates were lower (p < 0.05 versus PBMPhi). IL-10 had reduced effects on CD16 up- and HLA-DR down-modulation on CBMPhi (p < 0.05 versus PBMPhi). CD4-directed receptor modulation and deletion were reduced in the presence of CBMPhi (p < 0.05 versus PBMPhi). IL-10 failed to enhance their ADCC capacity, which was in contrast to PBMPhi (p < 0.05). These data suggest that CBMPhi have an impaired cytotoxic capacity via lower sensitivity toward IL-10.

Effect of dexamethasone on B7 regulation and T cell activation in neonates and adults.

The safety of dexamethasone for neonates has been questioned, partly because of its multiple unspecific effects on the immune system. Specific effects of dexamethasone on co-stimulatory and immune suppressive functions of neonatal compared with adult macrophages (MPhi) are not known. We evaluated the effect of dexamethasone on the expression and regulation of MPhi B7 family receptors (B7-1, CD80; B7-2, CD86) and on their ability to co-stimulate T cells. Cord blood macrophages (CBMPhi) and MPhi from healthy adults (PBMPhi) were isolated, and cell surface markers were phenotyped by flow cytometry. In tissue culture, cells were exposed to dexamethasone, interferon-gamma (IFN-gamma), cAMP, or a T cell mitogen (alphaCD3) and examined for their capacity to activate or destroy T cells. CBMPhi were less able to up-regulate CD80 and CD86 than PBMPhi (p < 0.05). Dexamethasone inhibited the up-regulation of CD80, CD86, and HLA-DR on PBMPhi and even more so on CBMPhi (p < 0.05 versus PBMPhi for CD80 and CD86). In the presence of dexamethasone, stimulation with alphaCD3 MAb enhanced cytotoxic functions of PMBMPhi and CB(mu)phi with an increase in deleted T cells, a reduced fraction of enlarged T cells, and an inhibition of T cell CD28 up-regulation, which again were more pronounced with CBMPhi (p < 0.05 versus PBMPhi). In conclusion, neonatal MPhi are exquisitely sensitive to the inhibitory effects of dexamethasone on B7 expression. Although perhaps producing the desired therapeutic effect, dexamethasone may do so in newborns at the expense of a near complete paralysis of MPhi-dependent T cell function.

Engagement of the CD137 (4-1BB) costimulatory molecule inhibits and reverses the autoimmune process in collagen-induced arthritis and establishes lasting disease resistance.

Agonistic antibodies against CD137 act as costimulators in the activation of CD8 T cells. They enhance the immune response against syngeneic tumour grafts and suppress T cell-dependent humoral immune responses in vivo. The present study was undertaken to determine whether suppression of antibody production by anti-CD137 mAb affects the development of collagen-induced arthritis (CIA). Male DBA/1J mice were immunized with bovine collagen II (CII) and treated with an agonistic anti-CD137 mAb or an isotype-matched control mAb. Mice were assessed regularly for macro- and microscopic signs of arthritis and for the appearance of collagen-specific antibody production. Interferon (IFN)-gamma determination, FACS analysis of splenocytes and histopathological joint examinations were performed after the animals were killed. Administration of anti-CD137 mAb at the time of collagen immunization blocked the development of disease and inhibited the humoral immune response against CII. Agonistic anti-CD137 mAb exhibited therapeutic efficacy even after the immune response to CII had succeeded and the disease became apparent. Furthermore, it induced a protective memory in the animals, enabling resistance to subsequent challenges with the pathogenic antigen. Our results suggest a key role for CD137 in the pathogenesis of CIA. This model provides insights into immunoregulatory conditions that control the pathogenesis of autoimmune diseases.

CD137 costimulatory T cell receptor engagement reverses acute disease in lupus-prone NZB x NZW F1 mice.

Systemic lupus erythematosus (SLE) is a CD4(+) T cell-dependent, immune complex-mediated, autoimmune disease that primarily affects women of childbearing age. Generation of high-titer affinity-matured IgG autoantibodies, specific for double-stranded DNA and other nuclear antigens, coincides with disease progression. Current forms of treatment of SLE including glucocorticosteroids are often inadequate and induce severe side effects. Immunological approaches for treating SLE in mice using anti-CD4 mAb's or CTLA4-Ig and anti-CD154 mAb's have proven to be effective. However, like steroid treatment, these regimens induce global immunosuppression, and their withdrawal allows for disease progression. In this report we show that lupus-prone NZB x NZW F(1) mice given three injections of anti-CD137 (4-1BB) mAb's between 26 and 35 weeks of age reversed acute disease, blocked chronic disease, and extended the mice's lifespan from 10 months to more than 2 years. Autoantibody production in recipients was rapidly suppressed without inducing immunosuppression. Successful treatment could be traced to the fact that NZB x NZW F(1) mice, regardless of their age or disease status, could not maintain pathogenic IgG autoantibody production in the absence of continuous CD4(+) T cell help. Our data support the hypothesis that CD137-mediated signaling anergized CD4(+) T cells during priming at the DC interface.

CD137-mediated T cell co-stimulation terminates existing autoimmune disease in SLE-prone NZB/NZW F1 mice.

T cell receptor recognition of antigen and major histocompatibility complex (signal 1) and T cell co-stimulation (signal 2) are essential for full T cell activation, differentiation, and survival of naïve and activated T cells. The proto-typical T cell co-stimulatory receptor, CD28, is a constitutively expressed type I integral transmembrane protein and member of the Ig superfamily. Since its discovery, additional T cell co-stimulatory receptors have been identified, a number of which belong to the tumor necrosis factor receptor superfamily. Included within this group is CD137 (4-1BB), an activation-inducible, type I transmembrane protein. Co-stimulation of T cells through CD137 effectively up-regulates CD8 T cell activation and survival. Although CD4(+) T cells are efficiently activated through the T cell receptor and CD137 receptor, it provokes CD4(+) T cell anergy and blockade of T-dependent humoral immune responses. Therefore, we tested whether agonistic anti-CD137 monoclonal antibodies (mAbs) would be effective in blocking the induction or progression of B cell dependent autoimmune disease. Herein, we demonstrate the protective effect of agonistic anti-CD137 mAbs in blocking systemic lupus erythematosus (SLE) disease progression in NZB/W F1 mice. Protection from SLE following anti-CD137 mAb treatment is not confined to rescuing mice from disease progression; rather, it fully protects young mice from developing any symptoms of disease. We further found that treatment of proteinuric mice with anti-CD137 blocks ongoing anti-dsDNA autoantibody production.

Expression and regulation of B7 family molecules on macrophages (MPhi) in preterm and term neonatal cord blood and peripheral blood of adults.

BACKGROUND: Macrophage (MPhi) receptors of the B7 family (CD80, CD86) play a crucial role in T cell activation: the lack of costimulation leads to anergy or apoptosis of reactive T cells. MPhi may differentiate into different subsets, the balance of which defines MPhi-dependent T cell reactions. The aim of this study was to examine neonatal and adult T cell response with respect to the costimulatory MPhi-potential in order to identify molecular predictors for the neonatal immune defense. METHODS: MPhi from peripheral blood (PBMPhi) or cord blood (CBMPhi) were stimulated with interferon-gamma (IFN-gamma), cyclic adenosine monophosphate (cAMP), CD40 ligand (CD40L), or alphaCD3. RESULTS: As compared to PBMPhi, CBMPhi showed a significantly decreased upregulation of CD80 and/or CD86 after stimulation with IFN-gamma, cAMP, CD40L, and alphaCD3. Accordingly, the proliferative T cell response was impaired in the presence of CBMPhi. The fraction of T cells that underwent cell death was higher, and blast formation was significantly lower than that observed in the presence of PBMPhi. CONCLUSIONS: CBMPhi, as compared to PBMPhi, delivered fewer costimulatory but more cytotoxic signals to T cells. These observations suggest that MPhi are one factor explaining the suboptimal immune defense of neonates and their increased susceptibility to infection. Using the costimulatory MPhi-potential as a predictor for immune responses requires a separate reference value system in neonatology.