Expression and variation of lymphocyte scavenger receptors in inflammatory diseases and cancer

Abstract

The immune system comprises cellular and humoral components that protect the organism against external and internal aggressions, such as pathogens and cancer. Therefore, it can distinguish healthy, self structures from exogenous or damaged structures. This is achieved with the so-called pattern recognition receptors (PRR) belonging to several protein superfamilies. These are specialized in the recognition of microbial-associated molecular patterns (MAMP) and damage-associated molecular patterns (DAMP). The present thesis focuses on a superfamily of family PRRs known as scavenger receptors, in particular, the CD5 and CD6 lymphocyte receptors. CD5 and CD6 have extracellular domains with scavenger receptor cysteine-rich (SRCR) structures. They are expressed on all T lymphocytes and a subset of B lymphocytes (B1a) involved in the production of polyreactive natural antibodies. Both receptors bind to the antigen-specific receptor complex of T (TCR) and B (BCR) cells. They transduce signals and modulate intracellular activation and differentiation signals mediated by the TCR and BCR. While the nature of CD5’s endogenous ligand is controversial, it is well known that CD6 binds to the adhesion molecule ALCAM/CD166, as well as to other proteins. CD5 and CD6 also act as PRRs by recognizing MAMPs from bacterial, fungal, viral, and parasitic origin. CD5 and CD6 play relevant roles in inflammatory diseases and cancer, as shown by association of single nucleotide polymorphisms (SNP) from at the CD5 and CD6 loci with the clinical course of lupus, rheumatoid arthritis, multiple sclerosis, psoriasis, melanoma and chronic lymphocytic leukemia. On this basis, it was hypothesized that changes in the expression level or the amino acid sequence of CD5 and CD6 would impact the susceptibility to or the phenotypical characteristics of immune mediated disorders, such as inflammatory diseases and cancer. Therefore, the objective of the present thesis is to assess the immunomodulatory effect of CD5 and CD6 gene expression and variation in experimental models of immune-mediated and in cohorts of immune-mediated disorders patients. To this end, CD5 and CD6 deficient mice were subjected to dextran sulphate sodium (DSS)-induced colitis, a mouse model of inflammatory bowel disease (IBD). Additionally, the effect of CD5, CD6 and CD166/ALCAM SNPs was analyzed on cohorts of IBD (n=1352 in Crohn’s disease and n=1013 in ulcerative colitis), primary Sjögren’s syndrome (n=212) and prostate cancer (n=376) patients by means of generalized linear models. CD5 and CD6 deficiency resulted in attenuated and exacerbated forms, respectively, of DSS-induced colitis, supporting their involvement in this experimental IBD model. Analyses in IBD patient cohorts showed association of CD5 SNPs with Crohn’s disease location (rs2241002) and requirement of biological therapies (rs2241002-rs2229177 haplotypes), and with poor ulcerative colitis prognosis (rs2241002-rs2229177 haplotypes), and association of CD6 SNPs with Crohn’s disease location (rs17824933) and prognosis (rs12360861), ulcerative colitis extent, and IBD extraintestinal manifestations (rs17824933). In primary Sjögren’s syndrome patients, analyses of individual SNPs showed association of CD5 rs2241002 with anti-Ro/La positivity, CD6 rs17824933 with neutropenia, and CD6 rs11230563 with leukopenia, neutropenia and peripheral nervous system involvement. Further analyses showed association of haplotypes from CD5 (rs2241002-rs2229177) with anemia and thrombocytopenia, CD6 (rs17824933-rs11230563-rs12360861) with cutaneous involvement, and CD166/ALCAM (rs6437585-rs579565-rs1044243 and rs6437585-rs579565-rs1044243) with disease susceptibility and several analytical parameters. In prostate cancer patients, the CD6 rs12360861 and CD166/ALCAM rs579565 SNPs were associated with biochemical recurrence, and CD5 rs2241002-rs2229177 haplotypes were associated with International Society of Urological Pathology grade ≥2. In summary, the results obtained in this thesis support a role for the CD5 and CD6 lymphocyte receptors, as well as the CD6 ligand CD166/ALCAM, in the pathogenesis of IBD, primary Sjögren’s syndrome and prostate cancer. These is in line with previous reports and position these receptors as relevant regulators of the immune system.

CD5 i CD6 són receptors transmembrana de tipus scavenger expressats en tots els limfòcits T i un subgrup de limfòcits B (B1a). Transdueixen senyals i modulen les senyals generades pels receptors clonotípics de cèl·lules T (TCR) i cèl·lules B (BCR). Si bé hi ha controvèrsia respecte la natura del lligand endogen de CD5, se sap que CD6 s’uneix a la molècula d’adhesió ALCAM/CD166, així com a altres proteïnes. A més, CD5 i CD6 reconeixen estructures conservades presents en bacteris, fongs, virus i paràsits. CD5 i CD6 juguen papers rellevants en algunes malalties inflamatòries i càncers, com es dedueix de l’associació de polimorfismes dels loci CD5 i CD6 amb el curs clínic del lupus, artritis reumatoide, esclerosi múltiple, psoriasi, melanoma i leucèmia limfàtica crònica. L’objectiu de la tesi és determinar l’efecte immunomodulador de l’expressió i variació de CD5 i CD6 en desordres immunomitjançats. Amb aquesta finalitat, es van sotmetre ratolins deficients en CD5 o CD6 a colitis induïda per dextransulfat de sodi (DSS), un model de malaltia inflamatòria intestinal (MII). A més, es va analitzar l’efecte de polimorfismes de CD5, CD6 i ALCAM/CD166 en cohorts de pacients de MII, síndrome de Sjögren primària i càncer de pròstata. La deficiència de CD5 i CD6 va resultar en formes atenuades i exacerbades, respectivament, de la colitis induïda per DSS, donant suport al seu paper en aquest model experimental de MII. A més, es va observar associació de polimorfismes de CD5 i CD6 amb la localització de la malaltia de Crohn, requeriment de teràpies biològiques, pronòstic de la colitis ulcerosa i presència de manifestacions extraintestinals. En pacients de síndrome de Sjögren primària, polimorfismes de CD5, CD6 i ALCAM/CD166 es van associar amb la susceptibilitat a la malaltia, presència de citopènies hematològiques, afectació nerviosa i cutània, i diversos paràmetres analítics. En càncer de pròstata polimorfismes de CD5, CD6 i ALCAM/CD166 es van associar amb la recidiva bioquímica i el grau ISUP. En resum, aquests resultats donen suport a un paper de CD5, CD6 i el lligand de CD6 CD166/ALCAM en la patogènesi de desordres immunomitjançats i els posicionen com a reguladors rellevants del sistema immunitari.