CD200 and pilocytic astrocytoma: We found CD200 protein expressed on a variety of human brain tumor tissue samples by western analysis: anaplastic oligoastrocytoma (n = 1), GBM (n = 3), meningioma (n = 1), ependymoma (n = 2), oligodendrogliomas (n = 1) and pilocytic astrocytoma (n = 1)(Figure 1A).