Graves’ disease (GD) is associated with T cell infiltration, but the mechanism for lymphocyte trafficking has remained uncertain. We reported previously that fibroblasts from patients with GD express IL-16, a CD4-specific chemoattractant, and RANTES, a C-C chemokine, in response to GD-specific IgG (GD-IgG). We unexpectedly found that these responses result from a functional interaction between GD-IgG and the insulin-like growth factor (IGF)-I receptor (IGF-IR). IGF-I and the IGF-IR-specific IGF-I analog, des(1–3), mimic the effects of GD-IgG. Neither GD-IgG nor IGF-I activates chemoattractant expression in control fibroblasts from donors without GD. Interrupting IGF-IR function with specific receptor-blocking Abs or by transiently transfecting fibroblasts with a dominant negative mutant IGF-IR completely attenuates signaling provoked by GD-IgG. Moreover, GD-IgG displaces specific 125I-labeled IGF-I binding to fibroblasts and attenuates IGF-IR detection by flow cytometry. These findings identify a novel disease mechanism involving a functional GD-IgG/IGF-IR bridge, which potentially explains T cell infiltration in GD. Interrupting this pathway may constitute a specific therapeutic strategy.

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Lymphocyte m at ant factor (LCF) is a lymphocyte cell product that mulat a m y response in CD4+ lymphoyte ocytes, and eopls. (3,10). These prior studies suggested that LCF-mediated events might occur following interaction of LCF with CD4 or a CD4-associated molecule.In this report we describe the molecular cloning of cDNA encoding human LCF and its expression in recombinant form (rLCF).t It is an unusual lymphokine with no significant homology to any previously described cytokines. We identify the requirement for rLCF autoaggregation to induce bioactivity and demonstrate a direct correlation between surfaceexpressed CD4 and LCF-induced migration. In addition, our data suggests that CD4 functions to transmit the migratory signal induced by rLCF. MATERIALS AND METHODSCells. Human peripheral blood mononuclear cells (PBMC) were isolated as described (1)(2)(3) Murine T-Cell Hybridoma Cell Lines. Three murine T-cell hybridoma cell lines were established as described (13,14

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Interleukin-16, a proinflammatory cytokine produced in CD8؉ lymphocytes, is synthesized as a precursor protein (pro-IL-16). It is postulated that the C-terminal region of pro-IL-16 is cleaved, releasing bioactive IL-16. To characterize IL-16 cleavage, we transfected COS cells with a cDNA encoding a ϳ50-kDa form of pro-IL-16. Transfected COS cells released a ϳ20-kDa IL-16 cleavage product shown to consist of the 121 C-terminal residues of pro-IL-16 by immunoblotting and amino acid sequencing. Cleaved IL-16, but not pro-IL-16, exhibited lymphocyte chemoattractant activity. A C-terminal ϳ20-kDa IL-16 polypeptide was also released when pro-IL-16 was treated with concanavalin A-stimulated CD8؉ lymphocyte lysate. Cleavage occurred after an Asp, suggesting involvement of a caspase (interleukin-1␤-converting enzyme/CED-3) family protease. Using recombinant caspases and granzyme B, we determined that pro-IL-16 cleavage is mediated only by caspase-3. Relevance to pro-IL-16 processing in primary lymphocytes was supported by identifying the p20 subunit of activated caspase-3 in stimulated CD8؉ lymphocytes and by inhibition of CD8 ؉ lymphocyte lysate-mediated cleavage with Ac-DEVD-CHO. Pro-IL-16 is a substrate for caspase-3, and cleavage by this enzyme releases biologically active IL-16 from its inactive precursor. 1 is a pleiotropic proinflammatory cytokine originally identified by Center and Cruikshank in 1982 (1, 2). IL-16 is produced and secreted predominantly by CD8 ϩ T lymphocytes, and it exerts chemoattractant, growth factor, and other activities on lymphocytes, monocytes, and eosinophils by interaction with CD4 (3). Biologically active IL-16 is secreted from CD8 ϩ T cells in response to antigen, mitogen, histamine (4), or serotonin stimulation (5), but the mechanism of IL-16 secretion remains undefined. Natural biologically active secreted IL-16 has a molecular mass of ϳ56 kDa by Sephadex molecular sieve chromatography, which appears to represent noncovalent association of four identical polypeptide chains (2, 6). Monomers of IL-16 migrate on SDS-PAGE in the range of 17-20 kDa (6). Recent evidence from cDNA cloning indicates that the mature and biologically active secreted IL-16 is derived from the C-terminal region of a larger intracellular precursor protein (pro-IL-16) (7). Like interleukin-1␤ (IL-1␤), the predicted amino acid sequence of IL-16 lacks a signal sequence, suggesting that maturation and release of IL-16 does not proceed by conventional mechanisms.Reviewing the predicted pro-IL-16 protein sequence, we identified three potential protease cleavage sites that might be targets for processing to release a C-terminal fragment in the size range of secreted IL-16. In this report we present evidence that COS cells transfected with IL-16 cDNA synthesize and naturally process pro-IL-16 and secrete the biologically active mature IL-16. Based on analysis of this processing in COS cells and experiments with primary lymphocytes, we determined that pro-IL-16 is specifically cleaved by a member of the caspase (interle...