The effect of a novel thiazole derivative, SM-8849, on experimental ar
thritis in mice was studied and compared to that of prednisolone. SM-8
849 and prednisolone reduced the incidence and severity of type II col
lagen-induced arthritis in mice, as assayed by clinical observation an
d histopathological studies. Although both agents inhibited type II co
llagen-induced delayed type hypersensitivity (DTH) in arthritic mice,
SM-8849 did not affect the production of humoral antibodies to type II
collagen. To examine the inhibitory mechanism of SM-8849, the effects
on T cell-dependent allergic inflammation were studied. SM-8849 clear
ly inhibited T cell-dependent reactions including staphylococcal enter
otoxin B (SEB)-induced arthritis, SEE-induced CD25 expression on T cel
ls and sheep red blood cell (SRBC)-induced DTH reaction. SM-8849, howe
ver, had no effect on the production of humoral antibody forming cells
in the spleen of mice immunized with SRBC. These results indicate tha
t inhibition of type II collagen-induced arthritis by SM-8849 is mainl
y due to the inactivation of T cells that are related to DTH reaction.