Inflammation and ectopic lymphoid structures in rheumatoid arthritis synovial tissues dissected by genomics technology: identification of the interleukin-7 signaling pathway in tissues with lymphoid neogenesis.
OBJECTIVE
In approximately 25% of synovial tissues from rheumatoid arthritis (RA) patients, infiltrates of T cells, B cells, and follicular dendritic cells (FDCs) are spatially organized into structures resembling lymph nodes with germinal centers. The remainder of the tissues lack FDCs and show either a diffuse or an aggregated T cell and B cell infiltrate. To gain more insight into this specific disease process, we sought to identify the genes expressed in RA tissues with ectopic lymphoid structures.


METHODS
Gene expression profiling of RA synovial tissues was determined by complementary DNA microarray analysis and quantitative real-time polymerase chain reaction. The presence of lymphoid follicles and localization of interleukin-7 (IL-7) in synovial tissue sections was determined by immunofluorescence staining using specific antibodies.


RESULTS
Findings of gene expression analysis confirmed previous reports that tissues with lymphoid structures showed elevated expression of CXCL13, CCL21, CCR7, and lymphotoxin alpha and beta messenger RNA. In addition, the tissues also showed enhanced expression of the chemokines CXCL12 and CCL19 and the associated receptors CXCR4 and CXCR5, which are important for the attraction of T cells, B cells, and dendritic cells. Pathway analysis revealed increased expression of genes involved in JAK/STAT signaling, T cell- and B cell-specific pathways, Fcepsilon receptor type I signaling in mast cells, and IL-7 signal transduction in the tissues with ectopic lymphoid follicles, accompanied by increased expression of IL-7 receptor alpha (IL-7Ralpha)/IL-2Rgamma chains and IL-7. Protein expression of IL-7 in RA tissues was localized within fibroblast-like synoviocytes, macrophages, and blood vessels and was colocalized with extracellular matrix structures around the B cell follicles.


CONCLUSIONS
Activation of the IL-7 pathway may play an important role in lymphoid neogenesis, analogous to its role in the development of normal lymphoid tissue.
Department of Molecular Cell Biology and Immunology, VU University Medical Center, 1007 MB Amsterdam, The Netherlands.
Trieneke C G
TC
Timmer
Belinda
B
Baltus
Mark
M
Vondenhoff
Tom W J
TW
Huizinga
Paul P
PP
Tak
Cornelis L
CL
Verweij
Reina E
RE
Mebius
Tineke C T M
TC
van der Pouw Kraan
D001172:Arthritis, Rheumatoid / Q000235:genetics* / Q000276:immunology / Q000473:pathology; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D015415:Biomarkers / Q000378:metabolism; D003713:Dendritic Cells / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D020869:Gene Expression Profiling; D023281:Genomics; D006801:Humans; D015851:Interleukin-7 / Q000235:genetics* / Q000378:metabolism; D008221:Lymphoid Tissue / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013583:Synovial Membrane / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D013585:Synovitis / Q000235:genetics* / Q000276:immunology / Q000473:pathology; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000473:pathology
D015415:Biomarkers; D015851:Interleukin-7; D012333:RNA, Messenger