Organ distribution of the ro (SS‐A) antigen in the guinea pig

Using an anti—Ro (SS‐A—specific “sandwich” enzyme‐linked immunosorbent assay (ELISA) and Western immunoblotting, we determined the Ro (SS‐A) content (both quantitative and qualitative) in saline‐perfused organs of the guinea pig. All tissue extracts contained substantial concentrations of Ro (SS‐A) antigen and could be grouped into 3 categories based on quantitative reactivity in the sandwich ELISA. The 60‐kd and 52‐kd molecular forms of Ro (SS‐A) present in tissue extracts were similar to those described in Wi‐L 2 extracts, and the 54‐kd molecular form of Ro (SS‐A) in guinea pig erythrocytes was similar to that found in human erythrocytes. The tissue distribution of the isoforms of Ro (SS‐A) was shown by Western immunoblotting to vary in different tissues, and the reactivity to the 60‐kd Ro (SS‐A) was correlated with the activity seen in the ELISA. Both the 60‐kd and 52‐kd Ro (SS‐A) bands in guinea pig liver extracts were very weak on Western immunoblots, in contrast to the high concentration of Ro (SS‐A) antigen in the ELISA. Other data suggest the possible existence of a unique form of Ro (SS‐A) in the liver. Guinea pig tissues have 4 Y RNA that are equivalent to the 4 human RNA—hY1, hY3, hY4, and hY5—present in HeLa cells, while guinea pig red blood cells have only one Y RNA, which is equivalent in size to human hY4. This heterogeneity of the Ro (SS‐A) antigen suggests that there is differential expression of the various Ro (SS‐A) genes in different tissues and expands the possibilities for tissue‐specific pathologic events involving the Ro (SS‐A)/anti—Ro (SS‐A) system.