Hyper-Ag-specific Ab Production in NC/Nga Mice is not associated with Deletion Polymorphism in the Promotor Region of the FcγRIIB Gene

Sakai Sakai

doi:10.3844/ajisp.2009.61.64

Abstract

Problem statement: NC/Nga (NC) mice produced high levels of ovalbumin (OVA)-specific IgG, IgG1 and IgG2a. We previously found deletion polymorphisms in the promoter region of fcgr2b in NC mice. To determine whether this mutation causes a hyper-humoral immune response, we generated congenic BALB/c mice carrying the NC-type fcgr2b allele (NC fcgr2b) and analyzed humoral immune response and FcγRIIB on germinal center (GC) B cells. Approach: BALB/c, NC and BALB/c- NC fcgr2b congenic mice were immunized with OVA 2 times at a 2-week-interval. Levels of OVA-specific IgG, IgG1 and IgG2a in serum were determined by ELISA. Four-color (anti-B220, anti-IgD, 2.4G2 and PNA) flow cytometry analysis was performed on splenocytes obtained from OVA-immunized mice and levels of FcγRIIB in GC (IgD-PNAhigh) and non-GC (IgD+PNAlow) B cells were analyzed. Results: Although perturbed up-regulation of FcγRIIB on GC B was observed in congenic mice, levels of OVA-specific Abs were comparable to those in BALB/c mice. Conclusion: NC fcgr2b affects the level of FcγRIIB in GC B cells but that the reduced FcγRIIB expression is not related to enhanced Ag-specific Ab responses in NC mice.

Highlights

FcγRIIB, a low-affinity FcR for IgG, acts as a negative feedback regulator by inhibiting B Cell Receptor (BCR)-mediated activation signal through an immunotyrosine-based inhibition motif when these two receptors are co-cross-linked by Ags and IgGcontaining immune complex[1,2,3]
We evaluated the expression of FcγRIIB in germinal center (GC) B cells because down-regulation of FcγRIIB in the GC has been reported in NZB mice, which have deletion mutation of fcg2b similar to that in NC mice[10,11,12]
Previous splenocytes obtained from OVA-immunized studies showed that expression of FcγRIIB in GC B cells is down-regulated in NZB mice[11,12]

Summary

INTRODUCTION

FcγRIIB, a low-affinity FcR for IgG, acts as a negative feedback regulator by inhibiting B Cell Receptor (BCR)-mediated activation signal through an immunotyrosine-based inhibition motif when these two receptors are co-cross-linked by Ags and IgGcontaining immune complex[1,2,3]. In the course of investigating these mechanisms, we found that NC mice produced a higher level of Ag-specifc IgG2a than did BALB/c mice and that NC mice have three deletion sites in regulatory regions of the FcγRIIB gene, two in the promoter region and one in the third intron[6]. We investigated the role of the NC-type fcgr2b allele (NC fcgr2b) in humoral immune response in (BALB/c x NC) x BALB/c or (BALB/c x NC) x NC backcross mice. The role of NC fcgr2b in Ab response is not fully understood. Establishment of congenic mice for NC fcgr2b made it feasible to examine the in vivo effect of fcgr2b allele polymorphism. We examined the effect of NC fcgr2b on Ag-specific Ab response in a congenic mouse strain

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSION