title: IL-6 production by human T lymphocytes. Expression in HTLV-1-infected but not in normal T cells.
abstract: IL-6 is an important regulator of humoral and cellular immunity. Although this cytokine is produced by diverse cell types, it is not known whether it is produced by T lymphocytes under physiologic conditions or which agents can induce T cell expression of IL-6. We analyzed the production of IL-6 by human peripheral blood T cells, human thymocytes, and human T cell lines. In pure populations of these cells, stimulated with different combinations of various mitogens and cytokines, IL-6 activity could not be detected. Analysis of purified T-alpha beta and T-gamma delta cells showed that neither T cell subset produced IL-6. Similarly, IL-6 mRNA was not detected in T cell or thymocyte populations for up to 48 h after stimulation. With the use of a PCR assay, IL-6 mRNA in T cells was found to be virtually negligible, and did not change after T cell activation. By in situ hybridization it was shown that the cells expressing IL-6 mRNA after mitogen activation of PBMC do not belong to the T cell lineage. To analyze whether human T cells express IL-6 in vivo, we examined lymphoid tissues by in situ hybridization. In normal human thymus there was no detectable signal for IL-6. Tonsils showed only few positive cells within the parenchyma, but strong expression of IL-6 by epithelial cells in crypts. In contrast to normal lymph node, which contained only rare cells positive for IL-6, a lymph node from a patient with Castleman's disease showed IL-6 expression in cells occupying the marginal sinus and interfollicular areas. Screening of various human T cell lines showed that all cell lines infected with HTLV-1 secrete IL-6 activity and express IL-6 mRNA. In addition, in vitro infection of peripheral blood T cells with HTLV-1 induced de novo synthesis and secretion of IL-6. Furthermore, IL-6 expression in HTLV-1-infected cells was enhanced by stimulation with IL-1 beta or TNF-alpha. In contrast, IL-6 was not detectable in non-infected T cell lines. These studies indicate that IL-6 may not be a physiologic product of human T lymphocytes and that infection of T cells with HTLV-1 results in aberrant expression of this cytokine.
authors.affiliation: Department of Molecular and Experimental Medicine, Research Institute of Scripps Clinic, La Jolla, CA 92037.
authors.forename: P M
authors.initials: PM
authors.lastname: Villiger
authors.forename: M T
authors.initials: MT
authors.lastname: Cronin
authors.forename: T
authors.initials: T
authors.lastname: Amenomori
authors.forename: W
authors.initials: W
authors.lastname: Wachsman
authors.forename: M
authors.initials: M
authors.lastname: Lotz
mesh_terms: D002460:Cell Line; D005786:Gene Expression Regulation; D015490:HTLV-I Infections / Q000276:immunology*; D006801:Humans; D066298:In Vitro Techniques; D007223:Infant; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger; D013601:T-Lymphocytes / Q000378:metabolism* / Q000382:microbiology
chemical_list: D015850:Interleukin-6; D012333:RNA, Messenger