Mixed connective tissue disease (
MCTD) is a rare autoimmune syndrome, signified by complex interactions between disease-related phenomena, including
inflammation, proliferative vascular arteriopathy, thrombotic events and humoral autoimmune processes. It is still controversial whether
MCTD is a distinct clinical entity among systemic
connective tissue diseases, although several authors consider that it is distinct and underline characteristic, distinct clinical, serological and immunogenetic features. The putative target of autoimmunity in
MCTD is U1-RNP, which is a complex of U1-RNA and
small nuclear RNP. Both the U1-RNA component and the specific
proteins, particularly U1-70K, engage immune cells and their receptors in a complex network of interactions that ultimately lead to autoimmunity,
inflammation, and tissue injury. U1-RNA is capable of inducing manifestations consistent with TLR activation. Stimulation of innate immunity by native
RNA molecules with a double-stranded secondary structure may help explain the high prevalence of autoimmunity to
RNA binding proteins.