However, the isotype of the antibody response may show the pathogenic mechanism or the role of these autoantibodies in the disease since IgM anti U1-RNP antibodies where predominantly found in SLE whereas IgG anti-U1-RNP in the absence of IgM anti-U1-RNP antibodies are found in MCTD [73]. Here, CD40LG is linked to mixed connective tissue disease.