Decreased expression of CD33 in peripheral mononuclear cells of Alzheimer's disease patients

• Recently, GWASs have identified CD33 gene as a genetic locus for AD.
• Our results showed that CD33 expressions in PBMCs were decreased in AD patients.
• CD33 may contribute to AD pathogenesis by involving inflammatory response.
• CD33 combining additional parameters may make an useful adjunct to future AD diagnosis.

Recently, two independent genome-wide association studies (GWAS) have identified CD33 gene, encoding cluster of differentiation 33 (CD33), as a genetic locus associated with Alzheimer's disease (AD). It has been suggested that CD33 may contribute to AD pathogenesis by involving in inflammatory response, synaptic dysfunction and cell membrane processes. We analyzed the expressions of CD33 in peripheral blood mononuclear cells (PBMCs) in AD group and control group by real-time quantitative polymerase chain reaction and flow cytometry. Expression of CD33 mRNA was down-regulated in AD patients comparing to controls (p = 0.001). The frequency of CD33 positive monocytes was also lower in AD patients than in controls (44.02 ± 22.17% versus 54.06 ± 21.86%, p = 0.001). Moreover, we observed a correlation between CD33 positive monocytes levels and Mini Mental State Examination (MMSE) score (r = 0.220, p < 0.05). According to receiver operating characteristic (ROC) curve analysis, the diagnostic accuracy for CD33 alone is relatively lower, while, combining with additional parameters might further improve the diagnostic value for AD.