What have we learned about GPER function in physiology and disease from knockout mice?

Estrogens, predominantly 17β-estradiol, exert diverse effects throughout the body in both normal and pathophysiology, during development and in reproductive, metabolic, endocrine, cardiovascular, nervous, musculoskeletal and immune systems. Estrogen and its receptors also play important roles in carcinogenesis and therapy, particularly for breast cancer. In addition to the classical nuclear estrogen receptors (ERα and ERβ) that traditionally mediate predominantly genomic signaling, the G protein-coupled estrogen receptor GPER has become recognized as a critical mediator of rapid signaling in response to estrogen. Mouse models, and in particular knockout (KO) mice, represent an important approach to understand the functions of receptors in normal physiology and disease. Whereas ERα KO mice display multiple significant defects in reproduction and mammary gland development, ERβ KO phenotypes are more limited, and GPER KO exhibit no reproductive deficits. However, the study of GPER KO mice over the last six years has revealed that GPER deficiency results in multiple physiological alterations including obesity, cardiovascular dysfunction, insulin resistance and glucose intolerance. In addition, the lack of estrogen-mediated effects in numerous tissues of GPER KO mice, studied in vivo or ex vivo, including those of the cardiovascular, endocrine, nervous and immune systems, reveals GPER as a genuine mediator of estrogen action. Importantly, GPER KO mice have also demonstrated roles for GPER in breast carcinogenesis and metastasis. In combination with the supporting effects of GPER-selective ligands and GPER knockdown approaches, GPER KO mice demonstrate the therapeutic potential of targeting GPER activity in diseases as diverse as obesity, diabetes, multiple sclerosis, hypertension, atherosclerosis, myocardial infarction, stroke and cancer.

Adoptive transfer of antithyrotropin receptor (TSHR) autoimmunity from TSHR knockout mice to athymic nude mice

We have recently shown that wild type mice are highly tolerant, whereas thyrotropin receptor (TSHR) knockout (KO) mice are susceptible to immunization with the mouse TSHR, the autoantigen in Graves' disease. However, because TSHR KO mice lack the endogenous TSHR, Graves-like hyperthyroidism cannot be expected to occur in these mice. We therefore performed adoptive transfer of splenocytes from TSHR KO mice into nude mice expressing the endogenous TSHR. Anti-TSHR autoantibodies were detected in approximately 50 % recipient mice 4 wk after adoptive transfer of splenocytes (5 × 10⁷/mouse) from TSHR KO mice immunized with adenovirus expressing mTSHR A subunit and persisted for 24 wk. Depletion of regulatory T cells by anti-CD25 antibody in the donor mice increased successful transfer rates without increasing antibody levels. Some recipient mice showed transient increases in thyroid-stimulating antibodies and T₄ levels 4-8 wk after transfer, but many became thyroid-blocking antibody positive and hypothyroid 24 wk later. Adoptive transfer of splenocytes from naïve TSHR KO mice transiently induced very low antibody titers when the recipient mice were treated with anticytotoxic lymphocyte antigen 4 and antiprogrammed cell death 1 ligand 1 antibodies for 8 wk after transfer. Histologically, macrophages infiltrated the retrobulbar adipose tissues and extraocular muscles in a small fraction of the recipients. Our findings demonstrate successful adoptive transfer of anti-TSHR immune response from TSHR KO mice to nude mice. Although the recipient mice developed only transient and infrequent hyperthyroidism, followed by eventual hypothyroidism, induction of orbital inflammation suggests the possible role of anti-TSHR immune response for Graves' orbitopathy.

A novel system for the efficient generation of antibodies following immunization of unique knockout mouse strains

BACKGROUND

We wished to develop alternate production strategies to generate antibodies against traditionally problematic antigens. As a model we chose butyrylcholinesterase (BChE), involved in termination of cholinergic signaling, and widely considered as a poor immunogen.

METHODOLOGY/PRINCIPAL FINDINGS

Jettisoning traditional laborious in silico searching methods to define putative epitopes, we simply immunized available BChE knock-out mice with full-length recombinant BChE protein (having been produced for crystallographic analysis). Immunization with BChE, in practically any form (recombinant human or mouse BChE, BChE purified from human serum, native or denatured), resulted in strong immune responses. Native BChE produced antibodies that favored ELISA and immunostaining detection. Denatured and reduced BChE were more selective for antibodies specific in Western blots. Two especially sensitive monoclonal antibodies were found capable of detecting 0.25 ng of BChE within one min by ELISA. One is specific for human BChE; the other cross-reacts with mouse and rat BChE. Immunization of wild-type mice served as negative controls.

CONCLUSIONS/SIGNIFICANCE

We examined a simple, fast, and highly efficient strategy to produce antibodies by mining two expanding databases: namely those of knock-out mice and 3D crystallographic protein-structure analysis. We conclude that the immunization of knock-out mice should be a strategy of choice for antibody production.

Humanized mice in translational biomedical research

The culmination of decades of research on humanized mice is leading to advances in our understanding of human haematopoiesis, innate and adaptive immunity, autoimmunity, infectious diseases, cancer biology and regenerative medicine. In this Review, we discuss the development of these new generations of humanized mice, how they will facilitate translational research in several biomedical disciplines and approaches to overcome the remaining limitations of these models.

The role of TNFalpha and IL-17 in the development of excess IL-1 signaling-induced inflammatory diseases in IL-1 receptor antagonist-deficient mice

IL-1 receptor antagonist (IL-1Ra)-deficient mice spontaneously develop several inflammatory diseases, resembling rheumatoid arthritis, aortitis, and psoriasis in humans. As adoptive T cell transplantation could induce arthritis and aortitis in recipient mice, it was suggested that an autoimmune process is involved in the development of diseases. In contrast, as dermatitis developed in scid/scid-IL-IRa-deficient mice and could not be induced by T cell transfer, a T cell-independent mechanism was suggested. The expression of proinflammatory cytokines was augmented at the inflammatory sites. The development of arthritis and aortitis was significantly suppressed by the deficiency of TNFalpha or IL-17. The development of dermatitis was also inhibited by the deficiency of TNFalpha. These observations suggest that TNFalpha and IL-17 play a crucial role in the development of autoimmunity downstream of IL-1 signaling, and excess IL-1 signaling-induced TNFalpha also induces skin inflammation in a T cell-independent manner.

Functional monoclonal antibodies to p75 neurotrophin receptor raised in knockout mice

In this study, p75NTREXONIII knockout mice were used as immune-naive hosts to produce functional antibodies to human p75NTR. Three monoclonal antibodies were produced and named MLR1, MLR2 and MLR3, and isotyped as IgG1, IgG2a and IgG2a, respectively. MLR1 and MLR2 bound to human p75NTR with higher affinity than the well-characterized ME20.4 in ELISA and also recognized p75NTR present on neurons in both rat and mouse. MLR1 and MLR2 bound to nerves known to express p75NTR following injection into Balb/C mice but not p75NTREXONIII knockout mice, indicating the antibodies are directed against the ligand binding extracellular region absent in knockout mice. Both MLR1 and MLR2 partially blocked NGF induced cell death in a mouse cell-line that expresses p75NTR but not TrKA. Importantly, intracerebroventricular injections indicated MLR2 was internalized within the cell bodies of mouse basal forebrain neurons, further demonstrating that this antibody is biologically active.

The role of Fas in the immune system biology of IL-2R alpha knockout mice: interplay among regulatory T cells, inflammation, hemopoiesis, and apoptosis

Introducing lpr mutation prevents early mortality associated with IL-2Ralpha knockout (KO) mice, prompting us to determine the role of Fas in the immune system biology of IL-2Ralpha KO mice. Consistent with a defect in CD4+CD25+ regulatory T (Treg) cell expression, spontaneous lymphocyte activation in lymphoid organs was observed in 6-wk-old mice. In 16- to 22-wk-old mice, infiltration of leukocytes was observed in bone marrow, colon, lung, pancreas, lacrimal gland, and salivary gland, but not in heart, thyroid, liver, stomach, small intestine, ovary, and kidney. In the lymphocytes-infiltrated bone marrow, B cell lymphopoiesis was blocked at pro-B to pre-B/immature B stage, culminating in an age-dependent B cell loss in the periphery. These phenotypes were also observed in IL-2Ralpha KO mice bearing the lpr mutation (DM mice), indicating Treg cell function and the phenotypes attributed directly to Treg cell abnormality are largely Fas-independent. However, anemia and body weight loss were partially prevented, tissue cell apoptosis was inhibited, and lifespan was improved in the DM mice, demonstrating Fas-dependent elements in these processes. Our age-dependent, lifelong analysis of IL-2Ralpha KO and DM mice supports a CD4+CD25+ Treg cell-based mechanism for the abnormal immune system biology observed in IL-2Ralpha KO mice and provides a global view of the interplays among Treg cells, multiorgan inflammation, hemopoiesis, and apoptosis.

Novel tumor necrosis factor-knockout mice that lack Peyer's patches

We generated a novel tumor necrosis factor (TNF) null mutation using Cre-loxP technology. Mice homozygous for this mutation differ from their "conventional" counterparts; in particular, they completely lack Peyer's patches (PP) but retain all lymph nodes. Our analysis of these novel TNF-knockout mice supports the previously disputed notion of the involvement of TNF-TNFR1 signaling in PP organogenesis. Availability of TNF-knockout strains both with and without PP enables more definitive studies concerning the roles of TNF and PP in various immune functions and disease conditions. Here, we report that systemic ablation of TNF, but not the presence of PP per se, is critical for protection against intestinal Listeria infection in mice.

Changes in innate and acquired immune responses in mice with targeted deletion of the dopamine transporter gene

The dopamine transporter (DAT) is responsible for the re-uptake of dopamine into presynaptic nerve terminals and thereby controls dopaminergic neurotransmission. Deletion of DAT results in a hyperdopaminergic phenotype and DAT(-/-) mice are characterized by pituitary hypoplasia, impaired maternal behavior, and increased locomotion. From earlier studies, we have evidence that the activity of the central dopaminergic system may play a role in determining immune reactivity and disease susceptibility. To further explore the functional relation between the dopaminergic system and the immune system, we investigated the activity of the immune system in DAT(-/-) mice. We show that in vitro, splenocytes from DAT(-/-) mice displayed reduced natural killer cell activity and reduced mitogen-induced cytokine responses. In contrast, LPS-induced cytokine production by macrophages was enhanced. In vivo, the cellular response to immunization with ovalbumine (OVA-induced delayed type hypersensitivity response) was significantly reduced. Interestingly, the OVA-induced humoral response (anti-OVA IgG) was increased in DAT(-/-) mice compared to wild-type animals. Plasma levels of catecholamines and corticosterone did not differ significantly between DAT(-/-) and wild-type animals. In conclusion, we show in the present study that interfering with the dopaminergic system has major consequences for both the acquired and the innate immune response.

A General Survey of Thymocyte Differentiation by Transcriptional Analysis of Knockout Mouse Models

The thymus is the primary site of T cell lymphopoiesis. To undergo proper differentiation, developing T cells follow a well-ordered genetic program that strictly depends on the heterogeneous and highly specialized thymic microenvironment. In this study, we used microarray technology to extensively describe transcriptional events regulating alphabeta T cell fate. To get an integrated view of these processes, both whole thymi from genetically engineered mice together with purified thymocytes were analyzed. Using mice exhibiting various transcriptional perturbations and developmental blockades, we performed a transcriptional microdissection of the organ. Multiple signatures covering both cortical and medullary stroma as well as various thymocyte maturation intermediates were clearly defined. Beyond the definition of histological and functional signatures (proliferation, rearrangement), we provide the first evidence that such an approach may also highlight the complex cross-talk events that occur between maturing T cells and stroma. Our data constitute a useful integrated resource describing the main gene networks set up during thymocyte development and a first step toward a more systematic transcriptional analysis of genetically modified mice.

Functions of toll-like receptors: lessons from KO mice

The innate immune response is a first-line defense system in which individual Toll-like receptors (TLRs) recognize distinct pathogen-associated molecular patterns (PAMPs) and exert subsequent immune responses against a variety of pathogens. TLRs are composed of an extracellular leucine-rich repeat (LRR) domain and a cytoplasmic domain that is homologous to that of the IL-IR family. Upon stimulation, TLR recruits a cytoplasmic adaptor molecule MyD88, then IL-IR-associated kinase (IRAK), and finally induces activation of NF-kappaB and MAP kinases. However, the responses to TLR ligands differ, indicating the diversity of TLR signaling pathways. Besides MyD88, several novel adaptor molecules have recently been identified. Differential utilization of these adaptor molecules may provide the specificity in the TLR signaling.

Dysfunction of macrophages in metallothionein-knock out mice

Metallothionein (MT) is a low molecular weight protein, rich in cystein residues, and induced by stimulation with several stresses such as heavy metals, chemical agents, oxygen radicals and irradiation. It is involved in metal metabolism, detoxification and radical scavenging and also participates in immune responses. In this communication, to study the role of MT in immune responses, we analyzed immune functions, especially macrophage functions in MT-knock out (MT-KO) mice in vitro. When compared with wild type counterpart (MT-WT) mice, macrophages from MT-KO mice showed a defect of phagocytic and antigen-presenting activity. Cytokine productions such as IL-1alpha, IL-6, IL-10 and IL-12 were reduced in macrophages from MT-KO mice. Furthermore, the expressions of CD80, CD86 and MHC class II molecules were also reduced in macrophages from MT-KO mice. No obvious dysfunction was observed in T cells and B cells. These results suggest that MT plays an important role in the regulation of immune responses, especially macrophage functions.

Antibody response and allogeneic mixed lymphocyte reaction in mu-, delta-, and kappa-opioid receptor knockout mice

The implication of opioid receptors in immune response has been studied using mu-, delta- and kappa-opioid receptor knockout mice. The mutant animals were compared to their wild-type (WT) counterparts for antibody (Ab) response to the prototype Ag keyhole limpet hemocyanin (KLH). Kappa-receptor deficient mice displayed higher Ab titers for either total Ig, IgM, IgG1 or IgG2a isotypes, whereas mu and delta animals behaved as wild-type mice. Therefore, endogenous kappa-receptor activation would tonically inhibit Ab response. Opioid receptor deficient mice were also used to investigate the immunosuppressive action of naltrindole, a delta-opioid receptor antagonist, shown earlier to inhibit graft rejection and the allogeneic mixed lymphocyte reaction (MLR) in vitro. Naltrindole and two related compounds inhibited MLR performed with lymphocytes from wild-type and delta-opioid receptor knockout mice. These compounds also suppressed MLR assayed with cells from triple mu/delta/kappa-opioid receptor mutants. We therefore demonstrate that naltrindole immunosuppressive activity is not mediated by any of the three mu-, delta- or kappa-opioid receptors, but by a target which remains to be discovered.

Beta 2 microglobulin knockout mice are resistant to lethal intraabdominal sepsis

beta 2 microglobulin knockout (beta2M-/-) mice lack CD8+ T and natural killer T cells. We hypothesized that beta 2M-/- mice are resistant to lethal intraabdominal sepsis. To test this hypothesis, mortality, cytokine production, and physiologic function were assessed in beta 2M-/- mice during sepsis caused by cecal ligation and puncture (CLP). beta 2M-/- mice survived significantly longer than wild-type mice after CLP but ultimately exhibited 100% mortality. Treatment of beta 2M-/- mice with anti-asialoGM1 to deplete natural killer cells conferred greater than 70% long-term survival. Compared with wild-type mice, beta 2M-/- mice treated with anti-asialoGM1 produced decreased amounts of proinflammatory cytokines and did not exhibit hypothermia or metabolic acidosis after CLP. Adoptive transfer of CD8+ T and natural killer cells into beta 2M-/- mice treated with anti-asialoGM1 re-established CLP-induced mortality. CD8 knockout mice treated with anti-asialoGM1, which are specifically deficient in CD8+ T and natural killer cells, exhibited 40% long-term survival after CLP. Furthermore, treatment of wild-type mice with antibodies to CD8 and asialoGM1 conferred a significant survival benefit compared with wild-type mice treated with nonspecific IgG. These findings demonstrate that beta 2M-/- mice treated with anti-asialoGM1 are resistant to CLP-induced mortality and that depletion of CD8+ T and natural killer cells largely accounts for the survival benefit observed in these mice.

Knock out models to dissect chemokine receptor function in vivo

Chemokines are a family of small proteins involved in numerous biological processes ranging from hematopoiesis, angiogenesis and lymphocyte trafficking to the extravasation and tissue infiltration of leukocytes in response to inflammatory agents, tissue damage and bacterial or viral infection. Chemokines exert their effects by binding to specific G-protein-coupled seven-transmembrane receptors. In vitro studies suggest that the chemokine system is highly redundant in that most chemokines bind to more than one receptor and most receptors bind multiple chemokines. Therefore, targeted deletion of chemokine receptors has proved to be a useful tool for determining the distinct biological role of these molecules in vivo.

Viral abrogation of stem cell transplantation tolerance causes graft rejection and host death by different mechanisms

Tolerance-based stem cell transplantation using sublethal conditioning is being considered for the treatment of human disease, but safety and efficacy remain to be established. We have shown that mouse bone marrow recipients treated with sublethal irradiation plus transient blockade of the CD40-CD154 costimulatory pathway develop permanent hematopoietic chimerism across allogeneic barriers. We now report that infection with lymphocytic choriomeningitis virus at the time of transplantation prevented engraftment of allogeneic, but not syngeneic, bone marrow in similarly treated mice. Infected allograft recipients also failed to clear the virus and died. Postmortem study revealed hypoplastic bone marrow and spleens. The cause of death was virus-induced IFN-alphabeta. The rejection of allogeneic bone marrow was mediated by a radioresistant CD8(+)TCR-alphabeta(+)NK1.1(-) T cell population. We conclude that a noncytopathic viral infection at the time of transplantation can prevent engraftment of allogeneic bone marrow and result in the death of sublethally irradiated mice treated with costimulation blockade. Clinical application of stem cell transplantation protocols based on costimulation blockade and tolerance induction may require patient isolation to facilitate the procedure and to protect recipients.

Impaired precursor B cell differentiation in Bruton's tyrosine kinase-deficient mice

Bruton's tyrosine kinase (Btk) is a cytoplasmic signaling molecule that is crucial for precursor (pre-B) cell differentiation in humans. In this study, we show that during the transition of large cycling to small resting pre-B cells in the mouse, Btk-deficient cells failed to efficiently modulate the expression of CD43, surrogate L chain, CD2, and CD25. In an analysis of the kinetics of pre-B cell differentiation in vivo, Btk-deficient cells manifested a specific developmental delay within the small pre-B cell compartment of about 3 h, when compared with wild-type cells. Likewise, in in vitro bone marrow cultures, Btk-deficient large cycling pre-B cells showed increased IL-7 mediated expansion and reduced developmental progression into noncycling CD2(+)CD25(+) surrogate L chain-negative small pre-B cells and subsequently into Ig-positive B cells. Furthermore, the absence of Btk resulted in increased proliferative responses to IL-7 in recombination-activating gene-1-deficient pro-B cells. These findings identify a novel role for Btk in the regulation of the differentiation stage-specific modulation of IL-7 responsiveness in pro-B and pre-B cells. Moreover, our results show that Btk is critical for an efficient transit through the small pre-B cell compartment, thereby regulating cell surface phenotype changes during the developmental progression of cytoplasmic mu H chain expressing pre-B cells into immature IgM(+) B cells.

Knockout mice: a paradigm shift in modern immunology

In the past decade, advances in genetic engineering and mouse knockout technology have transformed our understanding of the immune system. In particular, new perspectives on T-cell development, co-stimulation and activation have emerged from the study of single and multiple gene-knockout animals, as well as from conditional knockout and 'knock-in' mutants. Analysis of these animals has clarified important intracellular signalling pathways and has shed light on the regulatory mechanisms that govern normal immune responses and autoimmunity.

Insights into molecular mechanisms of contact hypersensitivity gained from gene knockout studies

Contact hypersensitivity (CHS), a dendritic-cell (DC)-dependent, T-cell-mediated skin immune response to reactive haptens, has been a subject of intense research for many years. The molecular mechanisms underlying CHS are complicated and are not fully understood. During the past few years, varieties of gene-targeted knockout mice have been used in the study of CHS. Such studies have contributed significantly to our understanding of the mechanisms responsible for the initiation of CHS. This review focuses on insights into molecular requirements for CHS gained from knockout studies.

Co-expression of N-cadherin and alpha-fetoprotein in stomach cancer

Although N-cadherin is necessary for organ formation originating in the endoderm, the expression of N-cadherin in gastric carcinoma and its role has not yet been reported. The present study was conducted to determine the pattern of immunohistochemical expression of E-cadherin and N-cadherin, using formalin-fixed, paraffin-embedded tissues from 97 primary gastric carcinomas, including 17 which were producing alpha-fetoprotein (AFP). Samples were subdivided into 50 tubular adenocarcinomas and 47 poorly differentiated adenocarcinomas. Results showed that E-cadherin was expressed in varying degrees in areas of cell adhesion between tumor cells, in 94 out of 97 cases studied. Three cases which showed no expression of E-cadherin were diagnosed as AFP-producing tumors by immunohistochemistry. Expression of N-cadherin was observed in varying degrees in the intercellular spaces between tumor cells in 11 tubular adenocarcinomas and in six poorly differentiated adenocarcinomas, including E-cadherin-negative cases, all of which were AFP positive. The present findings suggest a possible role for N-cadherin in gastric carcinoma.

Passive transfer of alloantibodies restores acute cardiac rejection in IgKO mice

BACKGROUND

Alloantibody is an intrinsic component of the immune response to organ transplants. Although alloantibodies have been correlated with decreased graft survival, the mechanisms of alloantibody-mediated injury remain largely undefined in vivo. In the present study, we have established a model of alloantibody-mediated graft injury using B10.A (H-2a) hearts transplanted to wild type (WT) or immunoglobulin knock out (IgKO) C57BL-Igh-6 (H-2b) mice.

METHODS

Alloantibodies were measured in the circulation and graft by flow cytometry and in immunofluorescence staining, respectively. Intragraft cytokine mRNA expression was evaluated using a competitive template reverse transcriptase polymerase chain reaction (RT-PCR) technique. P-selectin and von Willebrand factor expression were localized by immunoperoxidase staining. The capacity of alloantibodies to restore acute cardiac allograft rejection was tested by passive transfer of monoclonal antibodies (mAbs) against donor major histocompatibility complex (MHC) class I antigens to IgKO recipients.

RESULTS

B10.A cardiac allografts are rejected acutely by WT C57BL/6 recipients, but over 50% of the cardiac allografts survived more than 50 days after transplantation in IgKO mice. Competitive template RT-PCR on the cardiac transplants demonstrated similar levels of IL-1-alpha, IL-12 (p40), TNF-alpha, IL-2, IFN-gamma, IL-4, and IL-10 mRNA in WT and IgKO recipients 8-10 days after transplantation, indicating that macrophage- and T-cell-dependent immune responses were intact in IgKO recipients. The rejection of B10.A hearts in WT recipients was characterized by interstitial and perivascular cellular infiltration; IgG, IgM, and complement (C3) deposition; vascular cell injury and intravascular platelet aggregation; and release of von Willebrand factor and P-selectin. In IgKO recipients the lower degree of vascular injury in the absence of alloantibody responses was reflected by the lack of release of von Willebrand factor and P-selectin, which remained confined to cytoplasmic storage granules of endothelial cells and platelets. Acute rejection of cardiac allografts was restored to IgKO recipients by passive transfer of proinflammatory IgG2b mAbs against donor MHC; recipients injected with isotype-matched control mAbs did not reject. In contrast, passive transfer of IgG1 mAbs against donor MHC failed to restore acute rejection of cardiac allografts to IgKO recipients. Passive transfer of IgG2b, but not IgG1 mAbs was associated with endothelial cell activation and plate. let aggregation together with the release of preformed von Willebrand factor and P-selectin from storage granules.

CONCLUSIONS

Acute rejection of cardiac allografts can be reconstituted in IgKO recipients by passive transfer of IgG2b, but not IgG1 antibody. This model allows the mechanism of alloantibody-mediate graft injury to be dissected in vivo.

Insight into the physiological function(s) of uteroglobin by gene-knockout and antisense-transgenic approaches

To determine the physiological function(s) of uteroglobin (UG), a steroid-inducible, homodimeric, secreted protein, we have generated transgenic mice that either are completely UG-deficient due to UG gene-knockout (UG-KO) or are partially UG-deficient due to the expression of UG antisense RNA (UG-AS). Both the UG-KO and UG-AS mice develop immunoglobulin A (IgA) nephropathy (IgAN), characterized by microhematuria, albuminuria, and renal glomerular deposition of IgA, fibronectin (Fn), collagen, and C3 complement. This phenotype of both UG-KO and UG-AS mice is virtually identical to that of human IgAN, the most common primary glomerulopathy worldwide. The molecular mechanism by which UG prevents this disease in mice appears to center around UG's interaction with Fn. Since Fn, IgA, and UG are present in circulation and high plasma levels of IgA-Fn complex have been reported in human IgAN, we sought to determine whether UG interacts with Fn and prevents Fn-Fn and/or IgA-Fn interactions, essential for abnormal tissue deposition of Fn and IgA. Our coimmunoprecipitation studies uncovered the formation of Fn-UG heteromers in vitro and these heteromers are detectable in the plasma of normal mice, but not UG-KO mice. Further, high plasma levels of IgA-Fn complex, a characteristic of human IgAN patients, were also found in UG-KO mice. Finally, coadministration of UG + Fn or UG + IgA to UG-KO mice prevented glomerular deposition of Fn and IgA, respectively. Our results define a possible molecular mechanism of IgAN and provide insight into at least one important physiological function of UG in maintaining normal renal function in mice.

CD8(+) T cell knockout mice are less susceptible to Cowdria ruminantium infection than athymic, CD4(+) T cell knockout, and normal C57BL/6 mice

The role of T cells in immunity to Cowdria ruminantium was investigated by studying the responses to infection of normal, athymic, CD4(+) T cell knock out (KO) and CD8(+) T cell KO C57BL/6 mice. Normal C57BL/6 mice could be immunized by infection and treatment, and immunity was adoptively transferable from immune to naive mice by splenocytes. Following infection, athymic mice died sooner than normal mice (P=0.0017), and could not be immunized by infection and treatment. CD4(+) T cell KO mice were as susceptible to infection as normal mice and could be immunized by infection and treatment. In contrast, CD8(+) T cell KO mice were less susceptible than normal and CD4(+) T cell KO mice and 43% self-cured, while those that died did so after a prolonged incubation period. Antibody responses to C. ruminantium were CD4(+) T cell dependent, because responses were detected in immune normal and CD8(+) T cell KO mice but not in immune CD4(+) KO mice (P=0.005). Since CD8(+) T cell KO mice were less susceptible to infection, and since CD4(+) T cell KO mice could be immunized, it can be concluded that immunity to C. ruminantium can be mediated by both CD4(+) and CD8(+) T cells.

Combined natural killer cell and dendritic cell functional deficiency in KARAP/DAP12 loss-of-function mutant mice

KARAP/DAP12 is a transmembrane polypeptide with an intracytoplasmic immunoreceptor tyrosine-based activation motif (ITAM). KARAP/DAP12 is associated with several activating cell surface receptors in hematopoietic cells. Here, we report that knockin mice bearing a nonfunctional KARAP/DAP12 ITAM present altered innate immune responses. Although in these mice NK cells are present and their repertoire of inhibitory MHC class I receptors is intact, the NK cell spectrum of natural cytotoxicity toward tumor cell targets is restricted. KARAP/DAP12 loss-of-function mutant mice also exhibit a dramatic accumulation of dendritic cells in muco-cutaneous epithelia, associated with an impaired hapten-specific contact sensitivity. Thus, despite its homology with CD3zeta and FcRgamma, KARAP/DAP12 plays a specific role in innate immunity, emphasizing the nonredundancy of these ITAM-bearing polypeptides in hematopoietic cells.

Effect of a genetic deficiency of terminal deoxynucleotidyl transferase on autoantibody production by C57BL6 Fas(lpr) mice

Terminal deoxynucleotidyl transferase (TdT) adds nontemplate coded nucleotides (N additions) between the recombining ends of immunoglobulin and T cell receptor genes. These nucleotides add significant diversity to the Ig and TCR repertoires. Amino acids coded for by these nucleotides play a key role in the binding of self antigens by autoantibodies and autoreactive T cells. To determine the effect of a lack of N additions on autoantibody production, we bred the TdT knockout genotype onto the autoimmune C57BL/6-Fas(lpr) background. TdT-deficient mice had significantly lower sera anti-DNA and rheumatoid factor activity than their TdT-producing littermates. C57BL/6-Fas(lpr) TdT-deficient mice had shorter VH CDR3 regions and fewer VH CDR3 arginines [0.6% versus 4. 7%] than their TdT-producing littermates. These data indicate that the absence of TdT limited the production of anti-DNA antibodies and rheumatoid factors in C57BL/6-Fas(lpr) mice, likely due to constraints on Ig diversity secondary to the lack of TdT-derived N additions.

[Regulation of the immune response to intestinal nematode infections in mice]

Control of parasitic infections is dependent on mechanisms that limit invasion, reproduction or survival of the parasite, including elevated serum IgE, eosinophilia and intestinal mast cell hyperplasia. Studies with mice infected with Heligmosomoides polygyrus, Trichuris muris, Nippostrongylus brasiliensis and Trichinella spiralis have provided considerable information about immune mechanisms correlated with resistance and susceptibility. Activation and cytokine secretion of distinct Th cell subset leads to the generation of effective or ineffective responses resulting in clearance of the parasite load or maintenance of chronic infection. The induction of differential responses remains to be determined but is likely to be influenced at a number of levels including the host genetic background, involvement of accessory cells, activation of co-stimulatory molecules on antigen presenting cells. The regulation of responses to intestinal nematode infections is discussed.

Donor and recipient contributions of ICAM-1 and P-selectin in parenchymal rejection and graft arteriosclerosis: insights from double knockout mice

BACKGROUND

Mice with target gene deletions were used in an immunosuppressed, heterotopic mouse cardiac transplant model to investigate the effects of simultaneous deficiencies of ICAM-1 and P-selectin on late cardiac rejection.

METHODS

To determine the contribution of donor sources of ICAM-1 and P-selectin, ICAM-1/P-selectin gene deficient (I/P -/-) (n = 7) or wild type (n = 6) donor hearts were placed into CBA recipients. To study recipient sources of ICAM-1 and P-selectin, wild type donor hearts were placed into I/P -/- (n = 7) or wild type (n = 13) recipients. Recipients received a 30-day course of anti-CD4/8 mAb.

RESULTS

I/P -/- donor allografts had prolonged survival (52-57 days) compared with wild type allografts (49-51 days). I/P -/- donor allografts underwent parenchymal rejection with mononuclear cell infiltration and developed alpha-smooth muscle actin positive vascular thickening (30 +/- 7% luminal occlusion, n = 78 vessels). Wild type allografts had parenchymal rejection with vascular medial necrosis and an absence of arteriosclerotic thickening (10 +/- 8%, n = 75, p = 0.008). Using the reverse combination, allografts from I/P -/- or wild type recipients had similar graft survival (50-57 days), comparable but variable degrees of parenchymal rejection, and comparable vascular occlusion (22 +/- 15% vs 28 +/- 19%, p = 0.442).

CONCLUSION

We have shown that donor and recipient sources of ICAM-1 and P-selectin may have independent roles in leukocyte trafficking to the graft. Simultaneous interruption of donor ICAM-1 and P-selectin delays onset of parenchymal rejection. However, donor I/P deficiency permits arteriosclerotic development, perhaps by attenuating the alloimmune injury. In contrast, recipient deficiency alone does not altergraft outcomes suggesting that the donor is the critical site of ICAM-1 and P-selectin.

Cutting edge: generation of IL-18 receptor-deficient mice: evidence for IL-1 receptor-related protein as an essential IL-18 binding receptor

IL-18 is a proinflammatory cytokine that plays an important role in NK cell activation and Th1 cell response. Recently IL-1R-related protein (IL-1Rrp) has been cloned as the receptor for IL-18. However, the functional role of IL-1Rrp is still controversial due to its low affinity to IL-18 as well as the possibility of the presence of another high-affinity binding receptor. In the present study, we have generated and characterized IL-1Rrp-deficient mice. The binding of murine rIL-18 was not detected in Th1-developing splenic CD4+ T cells isolated from IL-1Rrp-deficient mice. The activation of NF-kappa B or c-Jun N-terminal kinase were also not observed in the Th1 cells. NK cells from IL-1Rrp-deficient mice had defects in cytolytic activity and IFN-gamma production in response to IL-18. Th1 cell development was also impaired in IL-1Rrp-deficient mice. These data demonstrate that IL-1Rrp is a ligand-binding receptor that is essential for IL-18-mediated signaling events.

gamma delta T-cells may interfere with a productive immune response in Plasmodium yoelii infections

Mice lacking alpha beta T-cells or gamma delta T-cells were infected with Plasmodium yoelii 17X NL (non-lethal) and followed for parasitaemia and cytokine production. While the parasitaemia in wild type mice resolved after reaching a peak value of 30 to 50%, it persisted in the -alpha beta T-cell mice until death. However, in the -gamma delta T-cell mice the peak parasitaemia was 12.5% of the levels seen in the wild type and -alpha beta T-cell mice and resolved faster than in the wild type mice. Higher levels of IL-10 and IFN-gamma were consistently found in the wild type and -gamma delta T-cell mice but not in the -alpha beta T-cell mice.

Susceptibility of immunodeficient gene-knockout mice to urinary tract infection

PURPOSE

Clinical and experimental evidence indicates that mucosal immunity to urinary tract infection involves B and T-cell functions. The present study was conducted to assess the susceptibility of immunocompetent and immunodeficient mice with genetically engineered deletions in T and B-cell functions to experimentally induced urinary tract infections (UTI) with Escherichia coli.

MATERIALS AND METHODS

Interferon-gamma (IFN-gamma), interleukin-4 (IL-4), IL-10, inducible nitric oxide synthase, T cell receptor (TCR) delta-chain and JHD B cell-deficient gene knockout mice and their immunocompetent controls were challenged with uropathogenic Escherichia coli. The bladders and kidneys were cultured for viable E. coli at time intervals after intraurethral challenge to assess susceptibility to an experimentally induced UTI.

RESULTS

Knockout mice with gammadelta-T cell or IFN-gamma deficiencies were more susceptible to UTI than immunocompetent mice or mice with immunodeficiencies in IL-10, IL-4, inducible nitric oxide synthase or antibody production (JHD).

CONCLUSIONS

These data support an important role for gammadelta-T cells and IFN-gamma in resistance to UTI in mice.

MU-opioid receptor-knockout mice: role of mu-opioid receptor in morphine mediated immune functions

The role of the mu-opioid receptor in immune function was investigated using mu-opioid receptor knockout mice (MOR-KO). Morphine modulation of several immune functions, including macrophage phagocytosis and macrophage secretion of TNF-alpha, was not observed in the MOR-KO animals, suggesting that these functions are mediated by the classical mu-opioid receptor. In contrast, morphine reduction of splenic and thymic cell number and mitogen-induced proliferation were unaffected in MOR-KO mice, as was morphine inhibition of IL-1 and IL-6 secretion by macrophages. These latter results are consistent with morphine action on a naloxone insensitive morphine receptor, a conclusion supported by previous studies characterizing a nonopioid morphine binding site on immune cells. Alternatively, morphine may act either directly or indirectly on these cells, by a mechanism mediated by either delta or kappa opioid receptors.

Role of interferon-gamma in the pathogenesis of LCMV-induced meningitis: unimpaired leucocyte recruitment, but deficient macrophage activation in interferon-gamma knock-out mice

Generally, interferon-gamma (IFN-gamma) is considered a critical regulator of T cell mediated inflammation. For this reason, we investigated the pathogenesis of lymphocytic choriomeningitis in mice with a targeted defect of the gene encoding this cytokine. Our results revealed that IFN-gamma is redundant in the afferent phase of the antiviral T cell response as well as a local mediator of this T cell mediated inflammatory disease. However, IFN-gamma may play an indirect role as it is involved in reducing extraneural infection that may compete with CNS for available effector cells. Analysis of the inflammatory exudate disclosed that leucocyte recruitment was unimpaired in the absence of IFN-gamma as was the upregulation of ICAM-1 and VCAM-1 on endothelium at the inflammatory site. However, local macrophage activation (production of tumor necrosis-alpha and NO) was significantly impaired. Notably, a viral peptide could also elicit a T cell mediated inflammatory response in virus-primed IFN-gamma knock-out mice, indicating that redundancy of this cytokine as a proinflammatory mediator is not restricted to inflammatory reactions triggered by an active infection. Thus, T cell mediated inflammation may be induced in the absence of IFN-gamma and local macrophage activation.

Altered spectra of hypermutation in antibodies from mice deficient for the DNA mismatch repair protein PMS2

Mutations are introduced into rearranged Ig variable genes at a frequency of 10(-2) mutations per base pair by an unknown mechanism. Assuming that DNA repair pathways generate or remove mutations, the frequency and pattern of mutation will be different in variable genes from mice defective in repair. Therefore, hypermutation was studied in mice deficient for either the DNA nucleotide excision repair gene Xpa or the mismatch repair gene Pms2. High levels of mutation were found in variable genes from XPA-deficient and PMS2-deficient mice, indicating that neither nucleotide excision repair nor mismatch repair pathways generate hypermutation. However, variable genes from PMS2-deficient mice had significantly more adjacent base substitutions than genes from wild-type or XPA-deficient mice. By using a biochemical assay, we confirmed that tandem mispairs were repaired by wild-type cells but not by Pms2(-/-) human or murine cells. The data indicate that tandem substitutions are produced by the hypermutation mechanism and then processed by a PMS2-dependent pathway.

Interleukin-7 (IL-7) knockout mice. Implications for lymphopoiesis and organ-specific immunity

Interleukin-7 (IL-7) is produced by both immune and non-immune cells including stromal cell lines, B-cells, monocytes/macrophages, follicular dendritic cells, keratinocytes, and gut epithelial cells. The development of IL-7 knockout mice aided to elucidate the role of this multifaceted cytokine in lymphopoiesis. Additionally, IL-7 gene-deleted mice may represent an excellent model in order to define the functional role of locally secreted IL-7 in organ-specific immunity and in anti-microbial responses as well. For instance, analysis of IL-7 gene-deleted mice revealed reduced numbers of total T-lymphocytes with preservation of the CD4/CD8 ratio and increased ratio of alpha beta + T-cells compared to gamma delta + T-cells. Transition of pro-T-cells to pre-T-cells was impaired. Cell marker analysis of thymocytes in IL-7 -/- mice suggested that IL-7 may induce expression of as yet unidentified cytokine receptors, and that IL-7 may also be critically involved in T-cell differentiation. However, there are clear differences in the requirements of alpha beta or gamma delta T-cells for IL-7. In general, IL-7 appears to serve as the major growth and differentiation factor for gamma delta T-cells. IL-7 -/- mice are characterized by a block of maturation of V gamma 3low, CD24+ T-cells to V gamma 3high, CD24low T-cells. Thus, IL-7 does not only represent a 'maintenance factor', but rather a cytokine required for successful thymic and extrathymic development and maturation of gamma delta T-cells. gamma delta + intestinal intraepithelial lymphocytes (iIEL) are absent in IL-7 -/- animals. In contrast, alpha beta + iIEL can be detected in IL-7 gene-deleted animals, but not in gamma c, or in JAK-3 deficient mice suggesting that alternative cytokines may be involved in development of iIEL alpha beta + T-cells, but not necessarily for gamma delta T-cells. To this end, IL-7 has predominantly been studied in the context of B- and T-cell development. With the availability of IL-7 gene-deleted mice, the paracrine effects of IL-7, which may be secreted in vivo by non-immune cells including keratinocytes or gut epithelial cells, can now be critically examined.

Interleukin-7, a non-redundant potent cytokine whose over-expression massively perturbs B-lymphopoiesis

Interleukin-7, originally described as a factor controlling the survival of B-cell progenitors, has been shown by gene knock-out technology to be a non-redundant cytokine. Of all single cytokine knock-out mice, those in which the IL-7 gene has been ablated show a profound defect in lymphocyte development. Likewise, mice in which signals emanating from the corresponding receptor, whether it be by ablation of the unique alpha or common gamma chain of the receptor, or by interference with downstream signalling elements generated by this receptor complex, also show profound defects in lymphocyte differentiation. Transgenic mice over-expressing the IL-7 gene also show profound changes in lymphocyte development which, in some instances can result in the development of lymphoid tumours. Here, we review some of these aspects of IL-7 biology with particular reference to an IL-7 over-expressing transgenic mouse line in which the IL-7 transgene is controlled by the mouse MHC class II promoter.

VH gene replacement in hyperselected B cells of the quasimonoclonal mouse

The primary repertoire of the quasimonoclonal mouse is monospecific. However, among peripheral B cells, there is a high frequency of variant cells with V(H) replacements, which are also hypermutated. We show in this work that these hyperselected cells expand in numbers as the animals increase in age, switch their isotypes, and with increasing age become the almost exclusive contributors to the pool of serum Ig. The fraction of such cells is higher in the peritoneum than in peripheral blood, supporting the view that the peritoneum is a site of production of nonspecific serum Ig. We have also isolated and partially sequenced the replacing V(H) gene segments from B220-positive, Id-negative cells, and mu-negative, lambda-positive (i.e., switched) cells, and matched them with their germline counterparts. V(H) families are represented proportional to the number of members in the germline, a finding that is consistent with the idea that environmental Ag pressure maintains the germline repertoire of V gene segment.

Genetic variation among 129 substrains: practical consequences

We designed a series of experiments to define the role of IFN-gamma in cellular interactions mediating graft rejection by assessing the rejection of H-Y disparate grafts in both ligand and receptor knockout mice and their control inbred strain. In the course of these studies it became apparent that neither knockout strain is histocompatible with the putative control and that the putative control is not histocompatible with either knockout strain. In the process of deducing why this might be so, it became apparent that the putative control is not an inbred strain of mouse. Thus, in the absence of rigorous genetic control, the utility of such knockout strains of mice for assessing the effects of cytokines and receptors in transplantation and autoimmunity is limited.

Phenotypic and functional characterization of mice that lack the type I receptor for IL-1

IL-1 alpha and IL-1 beta bind to receptors termed the type I and type II IL-1 receptors. The type I IL-1 receptor is responsible for specific signaling, while the type II IL-1 receptor functions as a nonsignaling decoy receptor. To determine the effect of a defect in IL-1-mediated signaling, mice have been produced with a genetically disrupted type I IL-1 receptor gene. Mice lacking type I IL-1 receptors are of normal vigor and exhibit no overt phenotype. B cells from type I IL-1R-/- mice activated in vitro with anti-IgM do not proliferate in response to IL-1, but do so in response to IL-4. Injection of murine IL-1 alpha does not induce detectable serum IL-6 levels in type I IL-1R-/- mice, but equivalent levels are produced in response to LPS. Type I IL-1R-/- mice have normal serum Ig levels and generate equivalent primary and secondary Ab responses as wild-type mice. In response to LPS, acute phase protein mRNA induction are equivalent in type I IL-1R-/- and wild-type mice. Type I IL-1R-/- mice do not differ from control mice in susceptibility to either a lethal challenge with D-galactosamine plus LPS or high dose LPS. Interestingly, ICE-/-/type I IL-1R-/- double mutant mice are resistant to high dose LPS. Type I IL-1R-/- mice backcrossed to the C57BL/6 background were as equally resistant as wild-type mice to Listeria monocytogenes.

Targeted disruption of the V(H) 81X gene: influence on the B cell repertoire

We have generated a mutant mouse in which the most D-proximal V(H) gene (V(H)81X) has been disrupted by introducing a neomycin-resistance gene into the V(H)81X exon by means of gene targeting in embryonic stem cells. The mutant mice generated are unable to express the V(H)81X gene but appear to display a normal pattern of B cell differentiation as well as normal numbers of bone marrow and peripheral B cells from fetal life all through ontogeny. They mount normal immune responses to several different antigens tested. In contrast, the distribution of V(H) gene rearrangements in the V(H)7183 family is altered in homozygous mutant mice. Thus, the antibody repertoire of the targeted mice is modified, at least as far as the expression of V(H)7183 genes is concerned.

Gene knockout mice as investigative tools in pathophysiology

An overview is given of the phenotype of mice with distinct deletions of genes for cytokines and some related proteins, which occur either naturally or as a result of homologous recombination. The use of such knockout mice for investigation of the pathophysiology of experimental disease is summarized. Understanding of the role of a given cytokine in pathogenesis has therapeutic implications, as the pathology may be prevented or attenuated by inhibition of the synthesis, release or activity of that cytokine.

A quasi-monoclonal mouse

As a model for studying the generation of antibody diversity, a gene-targeted mouse was produced that is hemizygous for a rearranged V(D)J segment at the immunoglobulin (Ig) heavy chain locus, the other allele being nonfunctional. The mouse also has no functional kappa light chain allele. The heavy chain, when paired with any lambda light chain, is specific for the hapten (4-hydroxy-3-nitrophenyl) acetyl (NP). The primary repertoire of this quasi-monoclonal mouse is monospecific, but somatic hypermutation and secondary rearrangements change the specificity of 20 percent of the antigen receptors on B cells. The serum concentrations of the Ig isotypes are similar to those in nontransgenic littermates, but less than half of the serum IgM binds to NP, and none of the other isotypes do. Thus, neither network interactions nor random activation of a small fraction of the B cell population can account for serum Ig concentrations.

Animal models of human disease. Transgenic and knockout models of autoimmunity: Building a better disease?

The development of transgenic and knockout technologies has driven an explosion in new animal models of disease. These engineered diseases are a departure from previous animal models in that pathological syndromes are created from a priori assumptions about how disease pathogenesis could develop. Such models have been useful in providing new information on the functions of effector molecules such as cytokines, and in following the behavior of lymphocytes in vivo. However, the contrived nature of the systems might generate false information, unless validated by careful reference to human disease and spontaneous disease in other animal models.

Cytokine knockout mice: possible application in toxicological research

Knockout mice obtained by homologous recombination technology may be valuable tools for in vivo investigations in toxico-pathogenesis. A short review of the phenotype of mice with distinct cytokine deletions, which occur either naturally or are obtained by homologous recombination, is given. The possible application in pharmacological and toxicological research is discussed with examples of endotoxic shock, hepatic, renal and haematological toxicity. Further applications include a wide variety of cutaneous, pulmonary, vascular, infectious and autoimmune pathology.