Abstract
In the course of studying the precipitin reactions between sera from patients with connective tissue diseases and the saline soluble extracts of young rabbit thymus acetone powder, a new precipitin system was observed, tentatively called the Tu system after the original serum.
The Tu antigen activity was unaltered by heating up to 60°C for 30 minutes, and was stable at pH values of 4 to 10. The precipitin activity was resistant to digestion by DNase and RNase, but partially sensitive to trypsin digestion, suggesting that a glycoprotein was associated with antigenicity. The average molecular weight of the Tu antigen was estimated to be 70, 000 as determined by Sephadex G-200 chromatography analysis. The Tu antigen was localized in the cell cytoplasma, but not in cell nuclei nor nucleoli, as observed by indirect immunofluorescence and the peroxidase enzyme antibody technique. Cell fraction analysis by centrifuge methods clarified that the Tu antigen activity was in the microsomal fraction, mostly in the rough endoplasmic reticulum fraction.
The Tu antibody was found in 31% of patients with progressive systemic sclerosis, in 20% with systemic lupus erythematosus, in 22% with mixed connective tissue disease and in 10-20% with other connective tissue diseases. The patients with this precipitin antibody in their sera also had antibodies to various non-histone nuclear protein antigens, including RNP, Sm, Scl-70, SS-A and SS-B.
The Tu system was completely different from immune systems previously reported by others which included anti thyroid-specific microsomal antibodies, ubiquitous tissue antigen (UTA) and liver/kidney microsomal systems because of the non-identical precipitin lines and the difference in their disease distribution.
