CD133 expression is associated with small round blue cell tumour morphology in human central nervous system neoplasms.

AIMS: CD133 is considered to be a marker for brain tumour-initiating cells. However, most data on CD133 are derived from animal or in-vitro studies. The aim of this study was to characterize CD133 expression, and the distribution and morphological features of CD133(+) cells, in primary and secondary human central nervous system (CNS) neoplasms. METHODS AND RESULTS: Tumours were analysed by real-time reverse transcription polymerase chain reaction, western blot, flow cytometry and immunohistochemistry. Our results show that only small round blue cell tumours (SRBCTs) exhibit strong and consistent CD133 expression. Interestingly, glioblastomas, large-cell carcinomas and sarcomas were negative for CD133. Only glioblastomas with a focal small-cell component exhibited CD133 immunoreactivity in the SRBCT component. In addition, CD133 expression did not correlate with the expression of other markers associated with stem cell differentiation, including CD15 and nestin. CONCLUSIONS: CD133 expression in human CNS neoplasms is independent of the grade of malignancy but strongly correlates with SRBCT morphology. Together with recent findings showing that CD133 is quickly upregulated upon hypoxia and that CD133(-) cells can also exhibit stem cell properties, our data strongly question the suitability of CD133 as a brain tumour stem cell marker in vivo.

Immune surveillance of the normal human CNS takes place in dependence of the locoregional blood-brain barrier configuration and is mainly performed by CD3(+)/CD8(+) lymphocytes.

Despite the blood-brain barrier (BBB) the human CNS is continuously screened by blood-derived immunological cells. In certain brain areas the local BBB configuration grants passage of large molecules, whereas others are better shielded. We investigated whether these regional BBB compositions are paralleled by differences in the degree of cellular immunosurveillance by investigating tissue from 23 normal human brains for several CD markers, FoxP3, granzyme B, and perforin. Our results provide evidence that immunosurveillance is associated with locoregional BBB configuration and is mainly performed by CD3(+)/CD8(+)/granzyme B(-)/perforin(-) lymphocytes.

Elevated HLA-E levels in human glioblastomas but not in grade I to III astrocytomas correlate with infiltrating CD8+ cells.

HLA-E is a ligand for the immune-inhibitory NKG2A receptor expressed on NK and T cells. To investigate HLA-E expression and immune cell infiltration in human astrocytic tumors in vivo, we analyzed normal CNS controls and astrocytomas of all WHO grades by immunohistochemistry. Both, CD8(+) immune cell infiltration and HLA-E expression were significantly higher in astrocytic tumors than in normal brain. Further, HLA-E expression levels and immune cell infiltration were significantly correlated in WHO grade IV glioblastomas. Thus, HLA-E overexpression in glioblastomas may be triggered by T and NK cell infiltration.

Albumin in immunohistochemistry: Foe and friend.

Immunohistochemical procedures constitute a high methodological value in both pathologic diagnostics and research. Staining quality depends on a large variety of interference factors. Primarily, background staining reduces the quality of evaluation by reducing the chromatic discrimination. For the identification of important interference factors, various incubation steps and composition of solutions recommended in routine protocols were altered or omitted in our study. Surprisingly, the most important effect concerning background staining reduction could be significantly attributed to the omission of albumin which usually is recommended as a reducer of background stainings. However, in contrast to this negative effect, albumin could also increase specific staining intensity. These findings lead to the recommendation of a careful use of albumin in immunohistochemistry because of the dichotomous effects mentioned above. Furthermore, these results imply that in case of a good specific staining pattern, the use of albumin in immunohistochemical solutions merely exerts significant negative background staining effects.

Choroid plexus tumors differ from metastatic carcinomas by expression of the excitatory amino acid transporter-1.

Tumors of the choroid plexus (CPTs) are rare neoplasms of neuroectodermal origin usually arising in pediatric patients. However, CPT may occur at any age, and their distinction from metastatic carcinomas is often difficult in adult cases. Because CPTs frequently show focal glial differentiation, we now investigated 35 CPTs (19 males and 16 females 0.3-70 years old; median age, 25.0 years), including 21 choroid plexus papillomas (CPPs), 5 atypical CPP, and 9 choroid plexus carcinomas regarding their expression of the excitatory amino acid transporter-1 (EAAT1, corresponding to rodent GLAST/GLAST-1) by immunohistochemistry. In addition, 77 metastatic carcinomas, including 64 adenocarcinomas with mostly papillary formations, derived from different organs were examined. Of the 35 CPTs, 23 (66%) showed membranous EAAT1 expression in variable numbers of tumor cells, including all atypical CPP and 3 of 9 choroid plexus carcinomas (33%). None of the metastatic carcinomas showed membranous immunostaining. Excitatory amino acid transporter-1 expression in CPT was significantly age dependent (P < .0001), with the proportion of EAAT1-positive tumor cells increasing with age, but not sex dependent. There was a highly significant difference between EAAT1 expression in CPT and in metastatic carcinomas (P < .0001). Establishing a cutoff value of 1% immunoreactive tumor cells served in adult cases to distinguish CPT from metastatic adenocarcinomas with 100% specificity and 70% sensitivity and was associated with positive and negative predictive values of 100% and 91%, respectively. Our findings indicate that EAAT1 immunohistochemistry may be useful in differentiating CPT from metastatic carcinomas.

OPA1, associated with autosomal dominant optic atrophy, is widely expressed in the human brain.

Autosomal dominant optic atrophy (adOA) is the most prevalent hereditary optic neuropathy with moderate to severe visual field loss and loss of retinal ganglion cells. The majority of cases of adOA is associated with mutations in the OPA1 gene. Northern blot analyses showed that OPA1 is expressed in all tissues examined, with the highest transcript level in the retina and in the brain. Here we addressed the cell type-specific expression of the OPA1 protein in human brain sections using immunohistochemical techniques and Western blotting. We studied OPA1 expression in normal cerebellum and various cerebral CNS tissue specimen of different areas obtained at autopsy from patients with no reported neurological symptoms or diseases and no neuropathological alterations using a polyclonal antibody raised against a C-terminal peptide of OPA1. We found OPA1 expression in somata and dendrites of neurons of the layers II-VI of the motor cortex and frontal brain. In the cerebellar cortex, OPA1 expression was detected in the Purkinje cell layer, in the granule cell layer and in the molecular layer. Double-labeling experiments showed also OPA1 expression in GFAP-positive astrocytes. Since mutations in the OPA1 gene specifically causes optic atrophy and occurrence of cerebral anomalies in adOA patients is not characteristic, this finding may suggest different cellular susceptibility of OPA1 in brain and retinal tissues.