A Restricted Role for FcγR in the Regulation of Adaptive Immunity.

By their interaction with IgG immune complexes, FcγR and complement link innate and adaptive immunity, showing functional redundancy. In complement-deficient mice, IgG downstream effector functions are often impaired, as well as adaptive immunity. Based on a variety of model systems using FcγR-knockout mice, it has been concluded that FcγRs are also key regulators of innate and adaptive immunity; however, several of the model systems underpinning these conclusions suffer from flawed experimental design. To address this issue, we generated a novel mouse model deficient for all FcγRs (FcγRI/II/III/IV-/- mice). These mice displayed normal development and lymphoid and myeloid ontogeny. Although IgG effector pathways were impaired, adaptive immune responses to a variety of challenges, including bacterial infection and IgG immune complexes, were not. Like FcγRIIb-deficient mice, FcγRI/II/III/IV-/- mice developed higher Ab titers but no autoantibodies. These observations indicate a redundant role for activating FcγRs in the modulation of the adaptive immune response in vivo. We conclude that FcγRs are downstream IgG effector molecules with a restricted role in the ontogeny and maintenance of the immune system, as well as the regulation of adaptive immunity

Antibody-independent thrombocytopenia in lactate dehydrogenase-elevating virus-infected mice.

Previously we demonstrated that antibody-mediated thrombocytopenia is strongly enhanced by lactate dehydrogenase-elevating virus (LDV) infection. Here we report that mice infected with LDV develop a moderate thrombocytopenia, even in the absence of immunoglobulins or Fc receptors. A similar decrease of platelet counts was observed after mouse hepatitis virus infection. LDV-induced type I interferon-independent thrombocytopenia was partly suppressed by treatment with clodronate-containing liposomes. Therefore, we conclude that the thrombocytopenia results from increased phagocytosis of nonopsonized platelets by macrophages

Macrophage-specific inhibition of NF-kappaB activation reduces foam-cell formation

Accumulation of lipid-laden macrophages is a hallmark of atherosclerosis. The relevance of the key transcription factor nuclear factor kappaB (NF-kappaB) for macrophage-derived foam-cell formation has not been unequivocally resolved. Transgenic mice lines were generated in which NF-kappaB activation is specifically inhibited in macrophages by overexpressing a trans-dominant, non-degradable form of IkappaBalpha (IkappaBalpha (32A/36A)) under control of the macrophage-specific SR-A promoter. Alanine substitution of serines 32 and 36 prevents degradation and retains the inactive NF-kappaB/IkappaBalpha (32A/36A) complex in the cytoplasm. Similarly, stable human THP1 monocytic cell lines were generated with integrated copies of IkappaBalpha (32A/36A) cDNA. Upon treatment with oxidized low-density lipoprotein (ox-LDL), murine peritoneal macrophages from transgenic IkappaBalpha (32A/36A) mice, as well as THP1/IkappaBalpha (32A/36A) clones, display decreased lipid loading after differentiation into macrophages. This is accompanied by increased expression of the transcription factors PPARgamma and LXRalpha as well as of the major cholesterol-efflux transporter ABCA1. Paradoxically, mRNA expression of the 'lipid-uptake' receptor CD36 is also increased. Since the net result of these changes is reduction of foam-cell formation, it is proposed that under specific inhibition of NF-kappaB activation, ABCA1-mediated cholesterol efflux prevails over CD36-mediated lipid influ

Involvement of Fcα/μ Receptor in IgM Anti-Platelet, but Not Anti-Red Blood Cell Autoantibody Pathogenicity in Mice.

IgM anti-mouse platelet autoantibodies cause thrombocytopenia by mediating uptake of opsonized thrombocytes, whereas IgM anti-erythrocyte autoantibodies induce anemia through a phagocytosis-independent cell destruction. In this article, we show that infection with lactate dehydrogenase-elevating virus, a benign mouse arterivirus, exacerbates the pathogenicity of IgM anti-platelet, but not anti-erythrocyte autoantibodies. To define the role of Fcα/μ receptor (Fcα/μR) in IgM-mediated thrombocytopenia and anemia, we generated mice deficient for this receptor. These animals were resistant to IgM autoantibody-mediated thrombocytopenia, but not anemia. However, the lactate dehydrogenase-elevating virus-induced exacerbation of thrombocytopenia was not associated with enhanced Fcα/μR expression on macrophages. These results indicate that Fcα/μR is required for the pathogenicity of IgM anti-platelet autoantibodies but is not sufficient to explain the full extent of the disease in virally infected animals

Analysis of CD97 expression and manipulation: antibody treatment but not gene targeting curtails granulocyte migration

The heptahelical receptor CD97 is a defining member of the EGF-TM7 family of adhesion class receptors. In both humans and mice, CD97 isoforms are expressed with variable numbers of tandemly arranged N-terminal epidermal growth factor-like domains that facilitate interactions with distinct cellular ligands. Results from treatment of mice with mAbs in various disease models have suggested a role for CD97 in leukocyte trafficking. Here, we aimed to thoroughly characterize the expression profile of CD97, and delineate its biological function. To this end, we applied a novel polyclonal Ab, which is the first antiserum suitable for immunohistochemistry, and combined this analysis with the study of Cd97-lacZ knock-in mice. We show that similar to the situation in humans, hematopoietic, epithelial, endothelial, muscle, and fat cells expressed CD97. Despite this broad expression pattern, the Cd97(-/-) mouse that we created had no overt phenotype, except for a mild granulocytosis. Furthermore, granulocyte accumulation at sites of inflammation was normal in the absence of CD97. Interestingly, application of CD97 mAbs blocked granulocyte trafficking after thioglycollate-induced peritonitis in wild-type but not in knock-out mice. Hence, we conclude that CD97 mAbs actively induce an inhibitory effect that disturbs normal granulocyte trafficking, which is not perturbed by the absence of the molecul

CD55 deposited on synovial collagen fibers protects from immune complex-mediated arthritis

CD55, a glycosylphosphatidylinositol-anchored, complement-regulating protein (decay-accelerating factor), is expressed by fibroblast-like synoviocytes (FLS) with high local abundance in the intimal lining layer. We here explored the basis and consequences of this uncommon presence. Synovial tissue, primary FLS cultures, and three-dimensional FLS micromasses were analyzed. CD55 expression was assessed by quantitative polymerase chain reaction (PCR), in situ hybridization, flow cytometry, and immunohistochemistry. Reticular fibers were visualized by Gomori staining and colocalization of CD55 with extracellular matrix (ECM) proteins by confocal microscopy. Membrane-bound CD55 was released from synovial tissue with phospholipase C. Functional consequences of CD55 expression were studied in the K/BxN serum transfer model of arthritis using mice that in addition to CD55 also lack FcγRIIB (CD32), increasing susceptibility for immune complex-mediated pathology. Abundant CD55 expression seen in FLS of the intimal lining layer was associated with linearly oriented reticular fibers and was resistant to phospholipase C treatment. Expression of CD55 colocalized with collagen type I and III as well as with complement C3. A comparable distribution of CD55 was established in three-dimensional micromasses after ≥3 weeks of culture together with the ECM. CD55 deficiency did not enhance K/BxN serum-induced arthritis, but further exaggerated disease activity in Fcgr2b (-/-) mice. CD55 is produced by FLS and deposited on the local collagen fiber meshwork, where it protects the synovial tissue against immune complex-mediated arthriti

Dystrophin expression pattern and morphological examination of del52hDMD/<i>mdx</i> mouse lines.

<p><b>A</b>) Western blot analyses of heart and quadriceps, incubated with either GTX (human and mouse specific) or Mandys106 (human specific). Wild type expression levels of human dystrophin were observed in hDMD/<i>mdx</i> mice. Notably, del52hDMD/<i>mdx</i>#37 mice expressed traces of human dystrophin, in both cardiac and skeletal muscle, while this was not observed in del52hDMD/<i>mdx</i>#35 and <i>mdx</i>(BL6) mice. <b>B</b>) Sections of the heart and quadriceps stained with human specific dystrophin antibodies. Expression of human dystrophin is at wild type level in hDMD/<i>mdx</i> mice as anticipated. Both C57BL/6J, <i>mdx</i>(BL6) and del52hDMD/<i>mdx</i>#35 mice did not express human dystrophin. Interestingly, in most fibers of del52hDMD/<i>mdx</i>#37 mice, human dystrophin was expressed at low levels. Haematoxylin and eosin staining revealed signs of degeneration and regeneration in the quadriceps of both del52hDMD/<i>mdx</i> strains, as evident by variation in fiber size, centralized nuclei and patches of fibrosis and inflammation. Overall pathology appeared to be slightly less extensive in del52hDMD/<i>mdx</i>#37 mice compared to <i>mdx</i>(BL6) and del52hDMD/<i>mdx</i>#35 mice. <b>C</b>) Almost no centralized nuclei were found in wild type mice, while half of the myofibers in <i>mdx</i>(BL6) and del52hDMD/<i>mdx</i>#35 mice had centrally located nuclei. The percentage in del52hDMD/<i>mdx</i>#37 mice was with 26% significantly lower. Data were based on manual counts of 5 randomly taken pictures of 2 males and 2 females per genotype. Asterisks indicate <i>P</i><0.01.</p

PCR analysis of targeted clones and confirmation of deletion exon 52 on RNA level.

<p>Single ES clones were cultured in 96-well plates and DNA was isolated and used as template in a multiplex PCR. Here the exons 46, 51 and 52 of the <i>hDMD</i> gene were analysed where exon 46 and 51 are positive controls and exon 52 the target to be deleted. <b>A</b>) An example is shown where candidate samples 2 and 5 are of interest because they are negative for exon 52 but positive for the control exons. <b>B</b>) For a large number of clones additional fragments were found for exon 52, suggesting non-homologues end joining (NHEJ) of TALEN induced double stranded breaks <b>C</b>) Representative image of LR-PCR performed on DNA of sub-clones of four exon 52 negative clones (9B4, 10H2, 11C9 and 11E7). LR-PCR was performed with primers targeting intron 51 (outside the targeting arm) and blasticidin (only present after homologous recombination), to rule out loss of PCR primer recognition sites by NHEJ and to confirm true targeting. <b>D</b>) RT-PCR was performed for RNA isolated from embryoid bodies of selected clones. The different fragments were isolated, purified and Sanger sequence analysed. In the wild type situation exon 52 was present, whereas in the properly targeted clones exon 52 was not present. This confirmed the exon 52 deletion on RNA level.</p