EXPRESSION OF A MEMBRANE FORM OF THE PREGNANCY-ASSOCIATED PROTEIN TJ6ON LYMPHOCYTES

TJ6 is a novel protein which has immunosuppressive activity and may ha ve a functional role in fetal allograft survival during pregnancy. Ini tial studies indicated that when mice were treated with an anti-TJ6 bi nding mAb early in pregnancy, the pregnancies were completely ablated and that TJ6 expression is enhanced dramatically during pregnancy. In addition we have cloned the cDNA for TJ6 which encodes a possible tran smembrane domain that may include six to seven transmembrane regions. Therefore, we examined TJ6 expression on PBL of pregnant and non-pregn ant women and found that TJ6 is expressed primarily on CD19(+) B cells from pregnant but non nonpregnant women. TJ6 was not expressed on CD3 (+) lymphocytes from either group but was expressed on CD56(+) cells f rom a small population of pregnant women which preliminary data indica te may correlate with the occurrence of spontaneous abortion in these women. Here we also show that TJ6 transcripts are highly expressed in the developing fetoplacental unit as well as in the developing thymus. We also begin to characterize the expression of TJ6 isoforms in an ac ute lymphocytic leukemia cell line (SB), murine thymus, and the develo ping murine fetoplacental unit, as well as the expression of a membran e from of TJ6 present on human lymphocytes during pregnancy. All of th ese cells and tissues expressed TJ6 proteins which were smaller than p redicted based on either the cDNA sequence or the in vitro translation even though they all expressed mRNA similar in size. The TJ6 isoforms varied in size from the 45-kDa isoform in SB cells to the 52-kDa isof orm of the fetoplacental unit to a 70-kDa isoform in murine thymus. Fl ow cytometric analysis also demonstrated that similar to the CD19(+) B cells from pregnant women, TJ6 is expressed on the surface of SB cell s. (C) 1994 Academic Press, Inc.