Complement-fixing antiperipheral myelin antibodies and C9 neoantigen in serum of patients with Guillain-Barré syndrome: quantitation, kinetics, and clinical correlation

JNK1 activation mediates C5b-9-induced P0 mRNA instability and P0 gene expression in Schwann cells

The protein zero (P0) glycoprotein is an important component of compact peripheral nerve myelin produced by the glial cells of the mammalian peripheral nervous system. P0 mRNA expression is reduced following exposure of Schwann cells to sublytic C5b-9, the terminal activation complex of the complement cascade. Sublytic complement treatment decreased P0 mRNA by 81% within 6 h and required C5b-9 assembly. C5b-9 induced a threefold increase in both JNK1 activity and c-jun mRNA within 20 and 30 min, respectively, compared with cells treated with either human serum depleted of complement component C7 (C7dHS) or medium alone. Sublytic C5b-9 stimulation, in the presence of the transcription inhibitor Actinomycin D, decreased P0 mRNA expression by 52%, indicating that mRNA was selectively destabilized. This effect was prevented by pretreatment with L-JNK inhibitor 1 (L-JNKI1). To study a potential inhibition of P0 gene transcription, we transfected Schwann cells with a P0 promoter-firefly luciferase construct. Sublytic C5b-9 stimulation of the transfected cells decreased luciferase activity by 82% at 6 h, and this effect was prevented by pretreatment with L-JNKI1 inhibitor. Our results indicate that the ability of C5b-9 in vitro to affect P0 gene expression is mediated via JNK1 activation that leads to enhanced mRNA decay and transcriptional repression of P0.

Sublytic C5b-9-stimulated Schwann cell survival through PI 3-kinase-mediated phosphorylation of BAD

Sublytic C5b-9 induces cell cycle activation, proliferation, and rescue from apoptosis in Schwann cells. The signaling pathways for C5b-9-mediated rescue were investigated. Following serum withdrawal, DNA fragmentation, detected by TUNEL and FACS analysis, was 56.7% +/- 7.3 and 91.9% +/- 2.4 in cultured sciatic nerve Schwann cells from 6-day-old rats after 18 h and 24 h, respectively. Apoptosis was confirmed by inhibition of DNA fragmentation in a dose-dependent manner by DMQD-CHO, a caspase-3 inhibitor. Treatment with sublytic C5b-9 generated with purified components (C5*9) or Ab+C7-depleted serum (C7dHS)+C7 rescued 89% and 86% of Schwann cells, respectively, as compared with cells treated with C5*6, C8, C9, or Ab+C7dHS. Sublytic C5b-9 increased Schwann cell PI-3 kinase and Akt activity maximally at 5 min 3.14 +/- 0.5-fold and 3.56 +/- 0.4-fold, respectively, over controls. ERK-1 activity was maximally stimulated 2.98-fold at 15 min. Inhibition of PI-3 kinase by LY294002 abrogated the C5b-9-mediated Schwann cell rescue from apoptosis, while inhibition of ERK-1 with PD098,059 did not. PI-3 kinase-Akt pathway activation by C5b-9 induced, within 15 min, a 6.34 +/- 1.2-fold increase in BAD phosphorylation at Ser 136, but not at Ser 112. Downstream Bcl-x(L) protein was increased 2.61-fold +/- 0.34-fold by 18 h and 3.9-fold +/- 0.84-fold by 24 h over controls. LY294002 prevented both BAD phosphorylation at Ser 136 and Bcl-x(L) protein induction, while PD098,059 did not. Our data indicated that sublytic C5b-9 rescued Schwann cell from apoptosis via activation of PI-3 kinase-Akt, BAD phosphorylation on Ser 136 and increased expression of Bcl-x(L). Sublytic C5b-9 detected on Schwann cell in vivo during inflammatory neuropathy may facilitate survival of Schwann cell capable of remyelination.

CD5 and immunoglobulin VH gene expression in B-cell lines from patients with autoimmune diseases

We studied the CD5 mRNA expression and VH gene family usage in Epstein-Barr virus (EBV)-immortalized B-cell lines derived from the blood of patients with type 1 diabetes (IDDM) of recent onset and of patients with polyneuritis cranialis multiplex (cranial neuritis; CN). After immortalization with EBV, at least 10 cell lines from each subject were tested for surface CD5 and CD20. mRNA expression was studied using cDNA probes for the six VH families as well as for CD5. The EBV lines from the IDDM patients used the VHIV family more frequently and VHI and VHII families less frequently than lines from controls. EBV lines from CN patients expressed the VHI and VHII families more often than those of the controls. When the IDDM and CN lines were compared, the lines derived from IDDM patients were found to use VH families I and II less frequently and VH families IV and V more frequently than lines from CN patients. There were no significant differences in the mean numbers of CD5+ B cells in the cell lines tested. More than half of the lines from each patient expressed CD5 at the mRNA level. No correlation was seen between the expression of surface CD5 and the level of CD5 mRNA expression. There was, however, a positive correlation between the usage of VH families III, V and VI, and the CD5 mRNA expression. In conclusion, the usage of VH families I to VI seemed to differ in patients with IDDM and CN. No differences were seen in the surface CD5 expression, but the lines expressing CD5 mRNA preferentially used the VH families III, V and VI.