ANALYSIS OF MURINE IGG ISOTYPE GALACTOSYLATION IN COLLAGEN-INDUCED ARTHRITIS

The galactosylation status of IgG from both control and arthritic DBA- 1 mice was determined by exoglycosidase sequencing and all anti-GlcNAc monoclonal based ELISA. Two to three weeks after arthritis onset mice with collagen-induced arthritis (CIA) showed a modest increase in IgG anti-GlcNAc reactivity against controls (0.644 +/- 0.080 and 0.530 +/ - 0.087, respectively, mean absorbance +/- SEM n = 4) consistent with previous literature reports. However, the authors were unable to detec t any significant changes in the galactosylation of purified IgG from arthritic and control mice using direct sequencing techniques (percent age G0 of 34.5% +/- 1.9 and 37.7% +/- 2.4, respectively, mean +/- SEM n = 4). It has been demonstrated that a correlation exists between per centage G0 and anti-GlcNAc reactivity for purified human IgG and sera samples, respectively; no such correlation was found for murine IgG an d sera. The galactosylation of purified polyclonal murine IgG isotypes was analysed on a separate group of arthritic mice selected for their high anti-GlcNAc reactivities. No significant differences were observ ed between control and arthritic mice. Immunoglobulin G isotype specif ic differences were found, with IgG(1) exhibiting the highest percenta ge G0 (45-48%) followed by IgG(2a) (27-37%), IgG(3) (20-32%) and IgG(2 b) the lowest (13-17%). The percentage G0 and anti-GlcNAc reactivity o f purified IgG(1) and IgG(2b) showed a narrow range of values when com pared to those of IgG(2a) and IgG(3) samples. Pooled sera from both ar thritic and control mice was used to purify large quantities of IgG(3) , which on analysis revealed a fourfold increase in anti-GlcNAc reacti vity in the arthritic sample compared to control. Paradoxically these same IgG(3) samples contained similar percentage G0 levels as determin ed by direct sequencing. The results suggest that IgG(1) and IgG(2b) e xhibit isotype selective oligosaccharide processing as little sample h eterogeneity could be observed. These two purified IgG isotypes displa yed a good correlation between percentage G0 and anti-GlcNAc reactivit y; this was in contrast to IgG(2a) and IgG(3). Immunoglobulin G(3) fro m arthritic mice may have G0 oligosaccharides selectively paired toget her with no net increase in percentage G0. This observation is discuss ed in detail as is the role of agalactosyl IgG in murine type II colla gen-induced arthritis.