Analysis of ancestral and functionally relevant CD5 variants in systemic lupus erythematosus patients.

OBJECTIVE: CD5 plays a crucial role in autoimmunity and is a well-established genetic risk factor of developing RA. Recently, evidence of positive selection has been provided for the CD5 Pro224-Val471 haplotype in East Asian populations. The aim of the present work was to further analyze the functional relevance of non-synonymous CD5 polymorphisms conforming the ancestral and the newly derived haplotypes (Pro224-Ala471 and Pro224-Val471, respectively) as well as to investigate the potential role of CD5 on the development of SLE and/or SLE nephritis. METHODS: The CD5 SNPs rs2241002 (C/T; Pro224Leu) and rs2229177 (C/T; Ala471Val) were genotyped using TaqMan allelic discrimination assays in a total of 1,324 controls and 681 SLE patients of Spanish origin. In vitro analysis of CD3-mediated T cell proliferative and cytokine response profiles of healthy volunteers homozygous for the above mentioned CD5 haplotypes were also analyzed. RESULTS: T-cell proliferation and cytokine release were significantly increased showing a bias towards to a Th2 profile after CD3 cross-linking of peripheral mononuclear cells from healthy individuals homozygous for the ancestral Pro224-Ala471 (CC) haplotype, compared to the more recently derived Pro224-Val471 (CT). The same allelic combination was statistically associated with Lupus nephritis. CONCLUSION: The ancestral Ala471 CD5 allele confers lymphocyte hyper-responsiveness to TCR/CD3 cross-linking and is associated with nephritis in SLE patients.

Identification of functionally relevant phoshorylatable serine clusters in the cytoplasmic region of the human CD6 lymphocyte surface receptor.

CD6 is a transmembrane receptor expressed by all T and a subset of B lymphocytes, where it physically associates with the antigen-specific receptor to modulate activation and differentiation processes through still poorly understood mechanisms. Its cytoplasmic tail lacks intrinsic catalytic activity but presents several consensus motifs for phosphorylation. The present work reports on the identification of two constitutively phosphorylated serine clusters (S480/482/484 and S560/562/565/567/568), which are embedded into Casein Kinase 2 consensus motifs, and are indispensable for proper mitogen-activated protein kinase activation following CD6 ligation. The data point to a novel level of regulation of CD6 function by intracytoplasmic serine phosphorylation.

Evolutionary and functional evidence for positive selection at the human CD5 immune receptor gene.

CD5 is a lymphocyte surface coreceptor of still incompletely understood function. Currently available information indicates that CD5 participates not only in cell-to-cell immune interactions through still poorly defined endogenous ligands expressed on hemopoietic and nonhemopoietic cells but also in recognition of exogenous and highly conserved microbial structures such as fungal ß-glucans. Preceding single nucleotide polymorphism (SNP) data analysis provided evidence for a recent selective sweep in East Asia and suggested a nonsynonymous substitution at position 471 (A471V; rs2229177) of the cytoplasmatic region of the CD5 receptor as the most plausible target of selection. The present report further investigates the role of natural selection in the CD5 gene by a resequencing approach in 60 individuals representing populations from 3 different continents (20 Africans, 20 Europeans and 20 East Asians) and by functionally assaying the relevance of the A471V replacement on CD5 signaling. The high differentiation pattern found at the nonsynonymous A471V site together with the low diversity, most of the performed neutrality tests (Tajima's D, Fu and Li's F* and D*, and Fu's Fs) and the predominance of a major haplotype in East Asians strongly argue in favor of positive selection for the A471V site. Importantly, anti-CD5 monoclonal antibody cross-linking unveiled significant differences among A471V variants regarding the mitogen-activated protein kinase (MAPK) cascade activation on COS7 and on human peripheral blood mononuclear cells. Similar differences on MAPK activation and IL-8 cytokine release were also observed upon exposure of HEK293 cell transfectants expressing the A471V variants to Zymosan, a ß-glucan-rich fungal particle. Taken together, the results provide evidence for the hypothesis of an adaptive role of the A471V substitution to environmental challenges, most likely infectious pathogens, in East Asian populations.