JOURNAL OF INTERFERON AND CYTOKINE RESEARCH 20:1001–1005 (2000) Mary Ann Liebert, Inc. Differences in Lymphocyte-Regulatory Activity Among Variants of Ovine IFN-t S ¸ABAN TEKIN, 1 ALAN D. EALY, 2,4 SHU-ZONG WANG, 3 and PETER J. HANSEN 1 ABSTRACT Interferon-t (IFN-t ) is secreted from trophectoderm of the ruminant preimplantation conceptus and func- tions during pregnancy to prevent luteolysis. In addition, IFN-t can inhibit proliferation of peripheral blood lymphocytes (PBL) and other cells. Several distinct ovine IFN-t (OvIFN-t ) gene variants exist; three of these (IFN-t 4, IFN-t 6d, IFN-t 11) differ in their ability to prevent luetolysis (IFN-t 4 . IFN-t 6d . IFN-t 11), inhibit growth of Daudi cells (IFN-t 4 . IFN-t 6d . IFN-t 11), and induce an antiviral state (IFN-t 4 . IFN-t 6d 5 IFN-t 11). The present objective was to compare variants for differences in ability to inhibit proliferation of phytohemagglutinin-stimulated PBL. At equal concentrations, IFN-t 4 was more inhibitory than IFN-t 6d, IFN- t 11, or an IFN-v control. Similar differences in potency were seen when IFN-t variants were tested at equal antiviral concentrations. Thus, the sheep trophectoderm secretes variants of IFN-t that differ in ability to reg- ulate lymphocyte function. The nature of the effect of the trophectoderm on endometrial lymphocytes may depend on the relative amount of each variant produced. 1001 I NTERFERON-t (IFN-t) IS A MEMBER of the type I IFN family that also includes IFN-a, IFN-b, and IFN-v. The closest member of the family is IFN-v, which has 75% amino acid identity with IFN-t and, like IFN-t, is 172 amino acids in length. (1) IFN-t evolved from IFN-v about 36 million years ago (2) after the divergence of pecoran ruminants from other ar- tiodactyls. Because of their recent evolution, genes for IFN-t are found only in pecoran ruminants, such as sheep, cattle, goats, deer, and giraffes. (2,3) Tissue expression of IFN-t is unique among IFN, as it is secreted only by the trophectoderm of periattachmentconceptusesfor a limited periodin early preg- nancy. Peak secretion, which occurs around days 12–17 in sheep, (4,5) and days 15–25 in cattle, (5,6) is coincident with the period when the uterus would ordinarily secrete luteolytic amounts of prostaglandinF 2a (PGF 2a ). Indeed, its primary role in pregnancy is to inhibit the pulsatile release of PGF 2a from the uterus to allow continued survival of the corpus luteum and the maintenanceof pregnancy. (7,8) IFN-t also differs from other IFN in that gene expression is not highly inducible by virus but rather is expressed constitutively within the trophectoderm. (9) Nonetheless, IFN-t possesses many biologic activities char- acteristic of other type I IFN, such as antiviral (10–13) and an- tiproliferative (10–12,14–16) activities, and the ability to induce ex- pression of genes that are normally regulated by other type I IFN, such as 29,59-oligoadenylate synthetase, (17) granulocyte chemotactic protein-2, (18) ubiquitin cross-reactive protein, (19) Mx protein, (20) and IFN regulatory factor-1 (IRF-1) and IRF- 2. (21) Among the immune cells whose growth is inhibited by IFN-t are peripheral blood lymphocytes (PBL) (10,14,15) and WC1 1 CD8 2 gd T cells. (22) IFN-t can stimulate expansion of WC1 2 CD8 1 gd T cells (22) and increase the cytotoxic activity of sheep and pig natural killer (NK) cells. (23) Regulationof lym- phocyte growth and activation may be important for prevent- ing rejection of the allogeneic conceptus, which in the sheep is susceptible to lysis by lymphokine-activated killer (LAK) cells, (24) or for determining the amount and nature of lympho- cyte-derived cytokines capable of regulating conceptus func- tion. (25) Immunoregulation of uterine lymphocytes by IFN-t is indicated by the observation in cattle that during pregnancy, maximal IFN-t secretion is associated with a decrease in the number of intraepithelial lymphocytes in the endometrium. (26) Multiple genes encode IFN-t in sheep and cattle, and sev- eral distinct genes are transcribed during early preg- nancy. (3,6,13,27–32) Recombinant proteins for some of these forms exist for ovine IFN-t (OvIFN-t) and include IFN-t4, IFN-t6d, IFN-t2c, and IFN-t11. (12,13) These proteins differ by no more than 13% in their primary amino acid sequences. (3,27,28) The variants IFN-t4, IFN-t6d, and IFN-t2c are apparently 1 Department of Animal Sciences, University of Florida, Gainesville, FL 32611-0920. 2 Department of Animal Sciences and 3 Department of Veterinary Pathobiology, University of Missouri, Columbia, MO 65211. 4 Present address: Department of Dairy and Animal Science, Pennsylvania State University, University Park, PA 16802. SHORT COMMUNICATION