Ro/SS‐A antigen in human platelets. Different distributions of the isoforms of Ro/SS‐A protein and the Ro/SS‐A–binding RNA

Ro/SS-A antigen is present in human platelets at a concentration that is approximately one-twentieth to one-thirtieth its concentration in lymphocytes, but the distribution of the Ro/SS-A isoforms is different from that in lymphocytes or red blood cells. The Ro/SS-A in platelets is largely the 52-kd form. Moreover, the 52-kd isoform in platelets is antigenically different from that in lymphocytes. In addition to the varied isoform distribution, a different distribution of the Ro/SS-A-binding RNA (hY RNA) is seen in platelets. While there are 4 hY RNA (hY1, hY3, hY4, and hY5) in lymphocytes and other nucleated cells, we have found that platelets contain only 2 hY RNA: hY3 and hY4. This hY RNA distribution is also different from that in red blood cells, which contain only hY1 and hY4. The different distributions of the Ro/SS-A components in lymphocytes, red blood cells, and platelets suggest different functional roles for the various protein and RNA components, as well as the possibility of different tissue-specific events related to the Ro/SS-A-autoanti-Ro/SS-A system.