CELLULA R IMMlJNOLOGY 134, 511-519 (1991) The Role of Interleukin-6 in Mitogenic T-Cell Activation: Detection of Interleukin-2 Heteronuclear RNA by Polymerase Chain Reaction’ GERD W ALZ, CHRISTOPHER STEVENS, BERND ZANKER, LARRY B. MELTON, STEVEN C. CLARK,* MANIKKAM SUTHANTHIRAN,~ AND TERRY B. STROM Department qf‘ilfedicine, Beth Israel Hospital and Harvard Medical School, Boston, Massachusc~trs 02215; tthe Rogosin Institute and Departments @Biochemistry and Medicine, Cornell University Medicul College, NW York, New York 10021; und *Genetics Institute, Cumhridge. Massachusetts 02140 Received October 18, 1990; accepted Jarmar), 6, 1991 It has been documented that interleukin-6 (IL-6) supports the proliferation of purified, anti- CD3stimulated murine T cells. We found that stimulation of human peripheral blood mononuclear cells (PBMCs) with anti-CD3 induced a significant accumulation of IL-6 mRNA, indicating that antigen-mediated T-cell activation may involve IL-6 release from accessory cells. Phytohemag- glutinin (PHA) had little effect upon IL-6 gene expression. In keeping with these findings. anti- IL-6 reduced but did not abolish anti-CD3-mediated proliferation of PBMCs, but had no significant effect upon PHA-stimulated proliferation. The addition of recombinant (r) IL-6 enhanced the proliferation of anti-CD3-stimulated PBMCs and increased the accumulation of IL-2 mRNA in PHA-stimulated PBMCs during the first 5 hr of culture. Nuclear run-off experiments did not reveal significant changes in IL-2 transcription in PHA plus rIL-6-treated PBMCs attempting to assume that IL-6 mediates stabilization of IL-2 mRNA. However, monitoring of partially spliced IL-2 mRNA by polymerase chain reaction revealed a clear increase in IL-2 heteronuclear RNA. Thus IL-6 increases the rate of IL-2 transcription which was not detectable by conventional in vitro transcription assays. We conclude that anti-CD3 triggers T-cell proliferation through a process that is partially but not entirely dependent upon release of IL-6. IL-6. in turn, supports IL-2 transcription. Insofar as anti-CD3 mimicks antigen-triggered activation of the T-cell receptor complex, IL-6 appears to support the early immune response by augmenting antigen-triggered IL-2 gene eXpr&OII. 0 1991 Academic Press, Inc. INTRODUCTION Interleukin-6 (IL-6)’ is a recently characterized cytokine (l-3) expressed in mono- cytes, fibroblasts, and various tumor cell lines (4-S). IL-6 expression can be elicited by various stimuli, including phorbol esters, double-stranded RNA, interferon-@, , IL- 1, tumor necrosis factor, and platelet-derived growth factor [reviewed in Ref (9)], although each of these stimulants is not effective in all IL-6 producing target cells. IL-6 induces B-cell differentiation (4, lo- 13), stimulates expression of acute phase proteins (14), enhances IL-3-dependent proliferation of multipotential hematopoietic ’ This work was supported by grants from the National Institute of Health. G. Walz is supported by an American Society of Transplant Physicians Fellowship. * Abbreviations used: PHA, phytohemagghttinin; PMA, phorbol myristate acetate; IL, interleukin: CHX. cycloheximide; pmRNA, partially spliced messenger RNA; PBMC, peripheral blood mononuclear cell; AC. accessory cell; PCR, polymerase chain reaction: mAb, monoclonal antibody. 511 0008-8749191 $3.00 Copyright 0 I99 I by Academic Press, Inc All rights of reproduction in any form reserved.