Interleukin-15 stimulates macrophages to activate CD4+ T cells: a role in the pathogenesis of rheumatoid arthritis?
Interleukin-15 (IL-15) is a proinflammatory cytokine that is overexpressed in rheumatoid arthritis (RA), a disease characterized by activation of monocytes/macrophages (MPhi), and by expansion of autoreactive CD4(+) T cells. We hypothesized that IL-15 plays a major role for this expansion of CD4(+) T cells and modulates the phenotype of monocytes/MPhi and their interaction with CD4(+) T cells. Here, we show that IL-15 enhances the proliferation of CD4(+) T cells from patients with RA in peripheral blood mononuclear cell cocultures. To further dissect the underlying mechanisms, we employed MPhi from IL-15(-/-) or IL-15 transgenic mice. These were induced to differentiate or were stimulated with IL-15. Here we show that addition of IL-15 during differentiation of MPhi (into 'IL-15MPhi') and overexpression of IL-15 by MPhi from IL-15(tg) mice leads to increased levels of major histocompatibility complex class II expression. This resulted in enhanced stimulation of antigen-specific CD4(+) T cells in vitro and was accompanied by reduced messenger RNA expression in MPhi for immunosuppressive SOCS3. The proliferation rates of IL-15MPhi and IL-15(tg)MPhi were high, which was reflected by increased p27(Kip1) and reduced p21(Waf1) levels. In view of high serum and synovial levels of IL-15 in patients with RA, our data suggest the possibility that this excess IL-15 in RA may stimulate monocytes/MPhi to activate the characteristic autoreactive CD4(+) T cells in RA.
Rückert
René
R
Department of Immunology and Cell Biology, Research Center Borstel, Parkallee 22, Borstel, Germany.
Brandt
Katja
K
Ernst
Martin
M
Marienfeld
Kathleen
K
Csernok
Elena
E
Metzler
Claudia
C
Budagian
Vadim
V
Bulanova
Elena
E
Paus
Ralf
R
Bulfone-Paus
Silvia
S
D000368:Aged; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000276:immunology; D049109:Cell Proliferation; D002478:Cells, Cultured; D018920:Coculture Techniques; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D006801:Humans; D019409:Interleukin-15 / Q000276:immunology*; D008213:Lymphocyte Activation / Q000276:immunology; D008262:Macrophage Activation / Q000276:immunology; D008264:Macrophages / Q000276:immunology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008875:Middle Aged; D010587:Phagocytosis / Q000276:immunology; D053647:Receptors, Interleukin-15 / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods
D018797:Cell Cycle Proteins; D000949:Histocompatibility Antigens Class II; D019409:Interleukin-15; D053647:Receptors, Interleukin-15