OX-2 membrane glycoprotein, also named CD200 (Cluster of Differentiation 200) is a human protein encoded by the CD200 gene.

The protein encoded by this gene is a type-1 membrane glycoprotein, which contains two immunoglobulin domains, and thus belongs to the immunoglobulin superfamily. Studies of the related genes in mouse and rat suggest that this gene may regulate myeloid cell activity and delivers an inhibitory signal for the macrophage lineage in diverse tissues. Multiple alternatively spliced transcript variants that encode different isoforms have been found for this gene

CD200 has been reported to be neuroprotective in neurodegenerative diseases. However, the potential protective effects of CD200 in germinal matrix hemorrhage (GMH) have not been investigated.

Feng et al. examined the anti-inflammatory mechanisms of CD200 after GMH. A total of 167 seven-day-old rat pups were used. The time-dependent effect of GMH on the levels of CD200 and CD200 Receptor 1 (CD200R1) was evaluated by western blot. CD200R1 was localized by immunohistochemistry. The short-term (24 h) and long-term (28 days) outcomes were evaluated after CD200 fusion protein (CD200Fc) treatment by neurobehavioral assessment. CD200 small interfering RNA (siRNA) and downstream of tyrosine kinase 1 (Dok1) siRNA were injected intracerebroventricularly. Western blot was employed to study the mechanisms of CD200 and CD200R1. GMH induced significant developmental delay and caused impairment in both cognitive and motor functions in rat pups. CD200Fc ameliorated GMH-induced damage. CD200Fc increased expression of Dok1 and decreased IL-1beta and TNF-alpha levels. CD200R1 siRNA and Dok1 siRNA abolished the beneficial effects of CD200Fc, as demonstrated by enhanced expression levels of IL-1beta and TNF-alpha. CD200Fc inhibited GMH-induced inflammation and this effect may be mediated by CD200R1/Dok1 pathway. Thus, CD200Fc may serve as a potential treatment to ameliorate brain injury for GMH patients ¹⁾.