Many attempts have been made to implicate hair follicle-specific autoa
ntibodies in the pathogenesis of alopecia areata (AA), a suspected aut
oimmune disease. Using the DEBR rat model for AA, we developed a refin
ed indirect immunofluorescent technique to examine the sera from indiv
idual rats for the presence of autoantibodies to the hair follicle and
to other tissues. Sera were tested on cryostat sections from normal P
VG/Ola rats and DEER rats. We found that DEER sera contained IgG autoa
ntibodies specific for hair follicle epidermal differentia. While indi
vidual sera revealed detailed differences, the target tissues identifi
ed were hair cortex and cuticle and the inner root sheath, especially
the Henle's layer. Some sera also contained autoantibodies specific fo
r skeletal muscle and nuclear components. Of 10 young prelesional rats
with apparently normal coats of hair, three had hair follicle autoant
ibodies and seven had skeletal muscle autoantibodies. Nine of 10 activ
e lesional rats with progressing hair loss had follicle autoantibodies
and four had skeletal muscle autoantibodies. All 10 established lesio
nal rats had follicle autoantibodies and one had muscle autoantibodies
. Control sera from eight PVG/Ola rats showed no specific positive sta
ining for hair follicle components or other tissues. Autoantibodies to
intracellular hair follicle differentiation products were readily det
ected in DEER rat sera. As these antibodies appeared to be generated a
fter the appearance of the mononuclear follicular infiltrate, such aut
oantibodies may be a secondary effect. We conclude that, while the pre
sence of autoantibodies in the DEBR rat model is associated with autoi
mmune activity, their role in the pathogenic progression of AA has yet
to be ascertained.