ヒト脳腫瘍における胎児性蛋白GP 68の発現

Mouse Fetal Brain Specific Protein "GP68" is Expressed in Human Brain Tumor Cells

　胎生11〜14日のマウス脳に特異的に出現する胎児性糖蛋白GP 68の，ヒト脳腫瘍における発現を検討した。マウス胎児脳からGP 68を分離・精製，ウサギに免疫し，抗マウスGP 68抗体を得た。これを用いて手術時に得た脳腫瘍43例と，剖検時に得たヒト脳の凍結組織を用い，免疫組織化学およびイムノブロットを行った。免疫染色の結果，抗GP 68抗体は正常脳では，血管内皮に弱陽性反応を示すのみで，脳実質細胞は全く染色されなかった。ところが脳原発腫瘍の内，神経膠腫の腫瘍細胞は，著しい染色性を示し，その染色の強度と，腫瘍悪性度とは正の相関を示した。イムノブロットの結果，正常脳では分子量68 KDの位置に薄いバンドが検出されるのみであったが，悪性神経膠腫では著しく濃いバンドが認められた。

　（結論）脳腫瘍のあるものは胎児性抗原GP 68に対する抗体で陽性染色された。イムノブロットで著しく濃いバンドが検出されたことから，GP 68蛋白そのものが，ある種の脳腫瘍で発現している事が示唆された。特に，神経膠腫では染色性と悪性度の相関も認めた。

It is well known that some fetal antigens are expres-sed in malignant tumor cells. Likewise, brain tumors, especially histologically malignant cases, may have any antigenic relationships with fetal brain.

So, we investigated this relationship by immuno-histochemical technique, utilizing a polyclonal antibody to mouse fetal stage-specific polypeptide "GP68".

We prepared GP68 from homogenate of head part of embryos at the 14th day of gestation mice by RCA-1 agarose column chromatography. And immunized it to Japanese white rabbits and the titer was measured by enzyme-linked immunosorbent assay.

We analyzed operatively resected brain tumors and autopsy brain tissues. Frozed tissues were fixed in cold acetone and immunostained with anti-GP68 serum according to biotin-streptoavidin peroxidase method. Remained tissues were homogenized in Laemmli's sam-ple buffer and electrophoresed. The proteins were trans-ferred to nitrocellulose menbrane and immunostained with anti-GP68.

Normal brain tissues were not positively stained, except for capillary endothelium which showed a weak staining. On the other hand, brain tumors of neur-oectodermal origin were positively stained in varying degrees, and other tumors were negative. It is especially noteworthy that, in astrocytoma cases, there exists a definite correlation between the intensity of stain and the degree of histological malignancy. Immunoblot studies demonstrated a very weak band at 68 KD in normal brain and meningioma. In contrast, very strong band at the same position was seen in malignant astrocytomas.

Theses result suggested that in brain tumors, espe-cially those of neuroectodermal origin, GP68 antigen is expressed and the degree of expression is related to their histological malignancy.

So this fetal antigen may be usuful for evaluation of biological malignancy of gliomas. In addition, GP68 may have some important roles in development of astrocytic cell lineage, because the period of expression of this antigen, 11th to 14th day of gestation, is a very important period for gliogenesis.