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

Abstract

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.