The Link Between CD6 and Autoimmunity: Genetic and Cellular Associations.

The cell surface glycoprotein CD6 is expressed on leukocytes and mediates T cell trafficking across endothelial cell barriers. There is evidence suggesting that CD6 is implicated in the pathogenesis of autoimmune diseases, including multiple sclerosis (MS) and rheumatoid arthritis (RA). CD166, the physiological ligand of CD6, is expressed on endothelial cells in the central nervous system and in the collagen tissue of joints as well as on the cell surface of synovial fibroblasts. Animal models and in vitro experiments have shown that CD166 facilitates leukocyte trafficking into the central nervous system and mediates interactions of synovial cells with T lymphocytes, thereby representing a possible common mechanism of pathogenesis in MS and RA. In recent years, genome-wide association studies (GWAS) have established a genetic link between CD6 and MS. The single nucleotide polymorphism (SNP) rs17824933 in the CD6 gene has been identified and validated as a genetic risk factor for the development of MS. The SNP is associated with altered CD4+ T cell functions and with the expression of alternative CD6 splice variants in T cells. Several other independent CD6 gene polymorphisms have been associated with disease susceptibility or with clinical features such as worse attack recovery in MS. In addition to the genetic associations found in MS, an allelic variant of the CD6 gene correlates with clinical response to tumor necrosis factor-α (TNF-α) inhibitors in patients with RA. Preliminary data indicate that anti-CD6 blockade may be a promising tool for the treatment of RA and psoriasis. Taken together, genetic associations and clinical observations provide new evidence for a role of CD6 in autoimmunity.

Epidemiology of Streptococcus pneumoniae serogroup 6 isolates from IPD in children and adults in Germany.

This study presents serogroup 6 isolates from invasive pneumococcal disease (IPD) before and after the recommendation for childhood pneumococcal conjugate vaccination in Germany (July 2006). A total of 19,299 (children: 3508, adults: 15,791) isolates were serotyped. Serogroup 6 isolates accounted for 9.5% (children) and 6.7% (adults), respectively. 548 isolates had serotype 6A, 558 had serotype 6B, 285 had serotype 6C, and 4 had serotype 6D. Among children, serotype 6B was most prevalent (7.5% of isolates) before vaccination, followed by 6A and 6C. After the 7-valent pneumococcal conjugate vaccine (PCV7), the prevalence of serotype 6B significantly decreased (p = 0.040), a pattern which continued in the higher-valent PCV period (PCV10, PCV13). Serotype 6A prevalence showed a slight increase directly after the start of PCV7 vaccination, followed by a decrease which continued throughout the PCV10/13 period. Serotype 6C prevalence remained low. Serotype 6D was not found among IPD isolates from children. Among adults, prevalence of both 6A and 6B decreased, with 6B reaching statistical significance (p = 0.045) and 6A showing a small increase in 2011-2012. Serotype 6C prevalence was 1.5% or lower before vaccination, but increased post-vaccination to 3.6% in 2011/12 (p = 0.031). Four serotype 6D isolates were found post-PCV7 childhood vaccination, and two post-PCV10/13. Antibiotic resistance was found mainly in serotype 6B; serotype 6A showed lower resistance rates. Serotype 6C isolates only showed resistance among adults; serotype 6D isolates showed no resistance. Multilocus sequence typing showed that sequence type (ST) 1692 was the most prevalent serotype 6C clone. Thirty-two other STs were found among serotype 6C isolates, of which 12 have not been previously reported. The four serotype 6D isolates had ST 948, ST 2185 and two new STs: 8422 and 8442. Two serogroup 6 isolates could not be assigned to a serotype, but had STs common to serogroup 6.