Molecular chaperones are targets of autoimmunity in Ro(SS-A) immune mice

We have used a murine model of experimental anti-Ro(SS-A) autoimmunity to d issect additional intermolecular interactions between the 52-kD Ro (Ro52) a nd 60-kD Ro (Ro60) autoantigens and molecular chaperones. Immune responses to members of the heat shock protein hsp70 and hsp90 families were measured by immunoblotting and ELISA in sera from mice immunized and boosted with p urified recombinant Ro52, Ro60 and La (SS-B). All Ro52 and Ro60 immune sera immunoblotted the inducible glucose-regulated protein grp78 and hsp70 spec ies but not constitutive hsc70 or hsp90. The kinetics of antibody productio n and reciprocal affinity purification experiments indicated that the grp78 and hsp70 responses were cross-reactive but distinct from immune responses to the primary Ro52 and Ro60 immunogens and the endoplasmic reticulum (ER) -resident chaperone calreticulin. No responses to molecular chaperones were detected in the La-immunized mice. Control immunizations indicated that th e recruited grp78 and hsp70 responses were specific for the Ro proteins and not due to immunization with denatured protein. The rapid spreading of imm unity to the inducible grp78 and hsp70 in Ro52- and Ro60-immunized mice sug gests that these components may co-localize and physically associate under certain physiological conditions which may promote autoimmunization. The po tential importance of the ER-resident chaperones grp78 and calreticulin is further supported by their co-localization with Ro in small apoptotic membr ane blebs and the finding of a novel putative grp78 binding motif in the ca rboxyl-terminal region of Ro52.