Epstein-Barr virus/C3d receptor (CR2, CD21) activated by its extracellular ligands regulates pp105 phosphorylation through two distinct pathways

We previously demonstrated that human C3d or pep16, a 16-amino acid synthetic peptide derived from human C3d, induced in vivo and in vitro tyrosine phosphorylation of pp105, an intracellular component found only in human cells that express CR2 at their surface. To determine the contribution of CR2 molecules to this enzymatic regulation, we first analyzed whether activation of CR2 by other extracellular CR2 ligands could trigger such regulation in cell extracts. Subsequently, we used cell extracts of either CR2-positive cells depleted in CR2 molecules by absorption with anti-CR2 antibodies or CR2-negative cells transfected with CR2 cDNA. We demonstrate here that pp105 phosphorylation was induced when CR2 was activated by C3d and pep16 as well as by gp350, the Epstein-Barr virus capsid protein or OKB7, an anti-CR2 monoclonal antibody (mAb). HB5, another anti-CR2 mAb, which did not activate B lymphocytes through CR2, did not induce pp105 phosphorylation. Thus, C3d, pep16, gp350, and OKB7 presented similar properties in activating CR2 to trigger pp105 phosphorylation and in regulating B lymphocyte proliferation, while HB-5 had no effect on either assays. Furthermore, our data demonstrate that the presence of CR2 activated by its extracellular ligands regulates pp105 phosphorylation through two distinct pathways: one which also requires the presence of non-activated CD19, and one which is independent of CD19. The involvement of CD19 in the first pathway was not due to the formation of putative CR2-CD19 complexes. Both pathways were TAPA-1 independent. This is the first demonstration that activated CR2 molecules can play a regulatory role in enzymatic function, such as phosphorylation, despite the absence of CD19 and TAPA-1.     

Mechanisms of effects of complement inhibition in murine collagen‐induced arthritis

Objective

To determine the mechanisms of amelioration of collagen‐induced arthritis (CIA) in DBA/1J mice by inhibition of complement activation.

Methods

Mice received 2 intradermal injections of bovine type II collagen (CII), on days 0 and 21. From day 21 (immediately after the second injection of CII) through day 35, mice received intraperitoneal injections of either phosphate buffered saline (PBS), a monoclonal mouse antibody to murine C5 (anti‐C5 antibody), or the C3 convertase inhibitor Crry‐Ig.

Results

On days 30 and 32, the clinical disease activity score was lower in mice treated with anti‐C5 antibody than in those treated with Crry‐Ig. Histopathologic evidence of joint damage was 75% lower in the mice treated with anti‐C5 antibody than in those treated with either PBS or Crry‐Ig. Spleen cells from mice receiving either form of complement inhibition exhibited decreased CII‐stimulated proliferation, whereas increased proliferative responses were exhibited by lymph node cells from mice treated with Crry‐Ig. Treatment with anti‐C5 antibody decreased production of IgG1 anticollagen antibody, while production of IgG2a antibody was inhibited by both complement inhibitory treatments. CII‐stimulated spleen cells from anti‐C5–treated mice produced lower levels of tumor necrosis factor α (TNFα) and interleukin‐10 (IL‐10) compared with those from mice treated with Crry‐Ig. Lower steady‐state messenger RNA (mRNA) levels for TNFα, interferon‐γ (IFNγ), IL‐18, and IL‐6 were observed in the joints of anti‐C5–treated mice, and for IFNγ and IL‐6 in mice receiving Crry‐Ig, all in comparison with PBS‐treated mice. However, mRNA levels for IL‐1β and TNFα were lower in the joints after treatment with anti‐C5 compared with Crry‐Ig.

Conclusion

These results indicate that inhibition of complement in CIA leads to decreased production of IgG2a antibody and suppressed CII‐induced spleen cell proliferation. The greater inhibitory effects on CIA of anti‐C5 antibody in comparison with Crry‐Ig may be attributable primarily to decreased levels of IL‐1β and TNFα mRNA in the joints.

     

MR imaging of facial nerve enhancement in Bell palsy or after temporal bone surgery

The authors evaluated magnetic resonance (MR) images obtained with intravenously administered gadolinium in ten patients who had facial paralysis and no facial nerve tumor. In patients with either Bell palsy (four patients) or facial paralysis after temporal bone surgery (six patients), intratemporal facial nerve enhancement was seen. Facial nerve enhancement on MR images proved to be a nonspecific finding.     

Progressive and regressive changes in the nucleus pulposus. Part I. The neonate

Magnetic resonance (MR) imaging, correlated with anatomic sections, was used to characterize the progressive and regressive changes in the nucleus pulposus in neonates. The spines of five fetuses and five full-term infants between 16 and 40 weeks old were studied. In anatomic sections, the nucleus pulposus was sharply demarcated from the anulus fibrosus, Sharpey fibers were conspicuous, and a plate of primitive notochord was evident in the equator of the disk. On long repetition time (TR)/long echo time (TE) or long TR/short TE MR images, Sharpey fibers (low signal intensity) and notochord (low signal intensity) could be differentiated from the high-signal-intensity nucleus pulposus and anulus fibrosus. The major differences between the fetal and infant spines were the amount of notochord in the disk and ossification in the vertebral body.     

Osteopetrosis: MR characteristics at 1.5 T

Four patients with proved osteopetrosis (three with the infantile malignant form and one with the benign form) were examined with magnetic resonance imaging at 1.5 T. All patients were studied in the coronal and sagittal planes using both short and long repetition time/echo time sequences. The infantile malignant form was characterized by a complete lack of signal from the marrow alternating with a signal intensity equivalent to that of the intervertebral disks, resulting in a "stepladder" appearance. In the benign form or after successful marrow transplantation in the infantile malignant form, intermediate or high signal intensity in the vertebrae was noted, suggesting the presence of some marrow elements.