QUANTITATIVE TRAIT LOCI DISPOSING FOR BOTH EXPERIMENTAL ARTHRITIS ANDENCEPHALOMYELITIS IN THE DA RAT - IMPACT ON SEVERITY OF MYELIN OLIGODENDROCYTE GLYCOPROTEIN-INDUCED EXPERIMENTAL AUTOIMMUNE ENCEPHALOMYELITIS AND ANTIBODY ISOTYPE PATTERN

Quantitative trail loci (QTL) controlling inflammatory diseases with d ifferent organ specificity may hypothetically either be unique for one disease or shared among different diseases. We have investigated whet her five non-MHC QTL controlling susceptibility to experimental arthri tis in the DA rat also influence myelin oligodendrocyte glycoprotein ( MOG)-induced experimental autoimmune encephalomyelitis (EAE) in an F2 intercross between inbred DA and PVG.RT1(a) rats. Two of the five chro mosome regions affecting arthritis in the DA rat also regulate phenoty pes of EAE. The DA allele at markers in Cia3 (collagen-induced arthrit is QTL) on chromosome 4 is associated with more severe EAE and high le vels of anti-MOG antibodies of the IgG2c subclass. Since production of antibodies of the IgG2c subclass may be stimulated by Th1 cells, and there is previous evidence that such cells promote EAE, it is possible that both of the studied phenotypes are controlled by the same gene o r genes regulating Th1-Th2 cell differentiation. Furthermore, we show that Oia2 (oil-induced arthritis QTL) on chromosome 4 regulates levels of anti-MOG antibodies of the IgG1 subclass and of anti-MOG IgE, but that this gene region does not affect clinical disease severity in our study. Since production of IgE and IgG1 may be stimulated by Th2 cell s, this QTL may also control Th1/Th2 bias. We conclude that Cia3 and O ia2 regulate MOG-induced EAE in rats. Furthermore, since both EAE and arthritis phenotypes co-localize to these gene regions, they may harbo r genes which are key regulators of pathogenic immune responses.