LSM2 and mixed connective tissue disease: To further verify the association among the cleaved 70 kDa U1-snRNP, B 19 infection and autoimmunity, serum samples from 3 different B 19 infected patients with MCTD or SLE were used to detect the U1-snRNP in COS-7 cells transfected with pEGFP, pEGFP-NS1 and pEGFP-NS1K334E.