An immunological study of human brain tumors concerning the brain specific protein S-100 and 14.3.2

Bovine besnoitiosis in a cattle herd in Sicily: an isolated outbreak or the acknowledgment of an endemicity?

Bovine besnoitiosis is a debilitating infectious disease caused by Besnoitia besnoiti (Apicomplexa; Sarcocystidae). The disease is mainly characterized by cutaneous and systemic signs, infertility in bulls, and abortion in cows. The current study describes an autochthonous outbreak of bovine besnoitiosis in Sicily, Southern Italy, being the first report of B. besnoiti infection in the island so far. In a cattle farm located in Syracuse province, a 4-year-old Belgian blue bull born in Sicily displayed typical clinical signs of the sub-acute/chronic disease phase with thickening of the skin of the scrotum and testicular degeneration. Histological examination of scrotal biopsies revealed the presence of several tissue cysts of B. besnoiti. The serological analysis of the herd using a commercial ELISA revealed a high seroprevalence (45 out of 55; 82%) of antibodies against B. besnoiti. Few seropositive animals (5 out of 45; 11%) showed clinical signs, cysts in vestibulum vaginae (1 out of 31; 3.2%), and testicular degeneration (4 out of 14; 28.6%) assessed by ultrasonographic investigations. The paucity of clinical signs associated with the high seroprevalence in the farm led to hypothesize that bovine besnoitiosis is endemic in the area though further studies are needed. Local practitioners should be more aware of the disease to facilitate the early detection of cases, prevent the spread of infection, and avoid economic losses and animal health problem.

Growing role of S100B protein as a putative therapeutic target for neurological- and nonneurological-disorders

S100B is a calcium-binding protein mainly expressed by astrocytes, but also localized in other definite neural and extra-neural cell types. While its presence in biological fluids is widely recognized as a reliable biomarker of active injury, growing evidence now indicates that high levels of S100B are suggestive of pathogenic processes in different neural, but also extra-neural, disorders. Indeed, modulation of S100B levels correlates with the occurrence of clinical and/or toxic parameters in experimental models of diseases such as Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, muscular dystrophy, multiple sclerosis, acute neural injury, inflammatory bowel disease, uveal and retinal disorders, obesity, diabetes and cancer, thus directly linking the levels of S100B to pathogenic mechanisms. In general, deletion/inactivation of the protein causes the improvement of the disease, whereas its over-expression/administration induces a worse clinical presentation. This scenario reasonably proposes S100B as a common therapeutic target for several different disorders, also offering new clues to individuate possible unexpected connections among these diseases.

S100 proteins as cancer biomarkers with focus on S100B in malignant melanoma

Although histochemical staining of the S100 protein family has been used for many years in the diagnosis of malignant melanoma, recent studies suggest one of the proteins comprising the S100 family, S100B, has particular utility in many aspects of the clinical management of malignant melanoma. This protein has been shown to be of use in staging malignant melanoma, in establishing prognosis, in evaluating treatment success and in predicting relapse. S100B is an independent prognostic factor and pretreatment circulating S100B concentrations predict duration of survival in melanoma patients. Survival is significantly longer in melanoma patients with normal S100B levels compared to those with elevated levels. Circulating S100B levels very sensitively detect metastatic growth of malignant melanoma, particularly in stage IV disease where S100B is certainly superior to other laboratory parameters. S100B concentrations reflect tumor mass. Serum S100B levels predict efficacy of treatment. Decreasing S100B concentrations reflect response to therapy while increasing S100B concentrations indicate tumor progression. Circulating S100B has a role to play in the decision to switch treatment regimens.

Congenital oligodendroglioma: a case report of a 34th-gestational week fetus with immunohistochemical study and review of the literature

A case of congenital oligodendroglioma occurring in a 34th-gestational week fetus is reported. The tumor was necrotic, hemorrhagic, and gelatinous. It covered the basal part of the brain, and almost the entire cerebellum was replaced by the tumor. The tumor cells had small, round, hyperchromatic nuclei and watery clear cytoplasm, and were arranged in a paved or alveolar pattern. Immunohistochemically, S100 protein, myelin-basic protein, neuron-specific enolase and Leu 7 were weakly positive for the cytoplasm, but glial fibrilliary acidic protein, synaptophysin, neurofilament, desmin, and vimentin were negative. Many tumor cell nuclei were positive for mutant p53 protein, and the labeling index was 85%. But there was no genetic alteration in exons 4 to 9 of p53 gene from the peripheral blood. The apoptosis index was 1.5%. Considering the p53 labeling index and the apoptosis index together, this congenital oligodendroglioma may be regarded as potentially malignant despite the benign morphological features.

An immunohistochemical screening of neurochemical markers in fungiform papillae and taste buds of the anterior rat tongue

The occurrence and distribution of several neurochemical markers were investigated. Numerous nerve fibres were shown, using antibodies to protein gene product (PGP) 9.5, neurone-specific enolase, calcitonin gene-related peptide (CGRP), substance P. neurokinin A or protein S-100. The presence of vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), neuropeptide tyrosine, dopamine-beta-hydroxylase (DBH), cholecystokinin/gastrin, glutamate and galanin was more scarce. Nerve fibres containing these above-mentioned markers were found at several locations, i.e. in the epithelium, connective tissue, and around blood vessels. In the taste buds, numerous PGP 9.5, neurone-specific enolase-, CGRP-, substance P-, neurokinin A- and protein S-100-containing structures were found, but few VIP and galanin ones. No immunoreactivity was found with antibodies against somatostatin, bombesin, enkephalin or dynorphin. These findings extend knowledge about the general as well as the neurochemical messenger-based innervation of rat fungiform papillae, forming a firm basis for future functional investigations of normal, experimental and also clinical materials.

Neurochemical markers of human fungiform papillae and taste buds

The presence of distribution of several neurochemical markers in human fungiform papillae and taste buds were investigated by the immunohistochemical technique. The gustatory cells of the taste buds are in synaptic contact with sensory nerve endings, and considering the taste buds strictly as specialized sensory organs, the amounts and distribution of some of the neurochemical markers were different to what we expected. For example, few structures showed immunoreactivity to the tachykinins substance P (SP), calcitonin gene-related peptide (CGRP), and neurokinin A (NKA) also for the peptides vasoactive intestinal polypeptide (VIP), neuropeptide tyrosine (NPY) and galanin, low amounts of immunoreactivity occurred. On the other hand, using antibodies to protein gene product 9.5 (PGP 9.5), protein S-100, and glutamate, numerous nerve fibres and/or immunoreactive cells were found in the fungiform papillae, in the epithelium, in the connective tissue and around blood vessels, as well as in or near taste buds. Incubation with the antibodies against somatostatin, enkephalin, bombesin, peptide histidine isoleucine amide (PHI), cholecystokinin (CCK)/gastrin and dopamine-beta-hydroxylase (DBH) was negative for the fungiform papillae. In conclusion, the present study has shown several immunoreactive structures using antibodies against certain neurochemical markers. Further investigations will hopefully correlate these morphological findings with functional taste perception data. Future studies of patients with taste disorders or other pathological changes correlated with taste and tongue will also be of utmost importance.

Laminin promotes differentiation, adhesion and proliferation of cell cultures derived from human acoustic nerve schwannoma

The influence of laminin on cell cultures derived from unilateral acoustic nerve schwannomas was investigated. Cell cultures were initiated from 12 schwannomas, removed via the enlarged middle cranial fossa approach. Tumor tissue was dispersed by collagenase treatment and cells seeded in uncoated or laminin-coated culture dishes. Confluent cultures were immunocytochemically characterized with antibodies against S-100, CD 68, factor VIII-related antigen and type IV collagen. Cell adhesion in response to different doses of laminin was evaluated with an electronic cell counter. The effect of laminin on cell proliferation was assessed by measuring the incorporation of 5-bromo-2'-deoxy-uridine (BRDU) into cellular DNA. Cells cultured on laminin as substrate appeared more differentiated with long, fusiform, cytoplasmic processes. Cultured cells stained positive for S-100, not for factor VIII-related antigen or CD 68. Only cells cultured on laminin deposited a dense extracellular network of type IV collagen. When laminin was added to the culture medium, cell attachment and proliferation was stimulated in a dose dependent manner. Maximal stimulation of both was observed with a laminin concentration of 50 micrograms/ml, which induced a nearly 2-fold increase in cell attachment and an approximately 66% increase in DNA content. Since laminin is a major component of the extracellular matrix in schwannomas, the possibility exists that laminin is also mitogenic for human neoplastic Schwann cells in situ.

Neurotrophic and neuroprotective effects of neuron-specific enolase on cultured neurons from embryonic rat brain

We previously reported that the gamma gamma-isozyme of enolase, NSE), one of the glycolytic enzymes, promoted the survival of embryonic rat neocortical neurons in culture, but alpha alpha-isozyme (non-neuronal enolase) had no effect. In the present study, the neurotrophic effects of NSE on cultured mesencephalic and spinal neurons from rat embryo were examined. NSE promoted the survival of neurons not only in neocortical cultures but also in mesencephalic and spinal cord cultures. Furthermore, NSE showed neuroprotective action on cultured neocortical neurons in a low-oxygen atmosphere. By contrast, non-neuronal enolase did not show any neurotrophic or neuroprotective activities. To clarify the mechanism of the neurotrophic effect of NSE, the binding of NSE to cultured neurons was determined by radio-receptor assay using 125I-labelled NSE. The specific binding, which was dose-dependent, saturable, and calcium-dependent, could be detected. These results suggest that NSE has neurotrophic and neuroprotective effects on rather a broad spectrum of neurons in the central nervous system. The existence of specific binding of NSE to cultured neurons suggests the possibility that receptor-like or carrier-like molecules on the neuronal surface are involved in the neurotrophic activity of NSE.

Immunohistochemical studies of neurochemical markers in normal human buccal mucosa

The content of various substances, such as regulatory peptides, hormones and structural proteins, was investigated in normal buccal mucosa using indirect immunofluorescence. Thin nerve fibres, which from a morphological point of view were most probably sensory, showed immunoreactivity for substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide K (NPK) and neurokinin A (NKA). Also galanin (GAL), gamma-melanocyte stimulating hormone (gamma-MSH) and somatostatin (SOM) stained thin fibres were found in the propria, which were, however, few in number and the gamma-MSH staining was weak. CGRP, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI) and neuropeptide Y (NPY) immunoreactive nerve fibres were observed in close connection to blood vessels. SOM positive cells with processes were found, mostly scattered, in the connective tissue. A population of cells within the epithelium also showed somatostatin immunoreactivity. Protein S-100 (S-100) stained distinct populations of cells at two separate locations. In the propria, cells with one or two slender processes were seen, being mostly single but sometimes forming groups. In the epithelium, dendritic cells with many processes with or without 'spines' were observed, mainly located to the basal layer of the lamina epithelialis. Single nerve fibres and nerve bundles were also stained. Neurofilament (NF) positive fibres, singly and in bundles, as well as endorgan-like structures were seen. Neuron-specific enolase (NSE) and protein gene product 9.5 (PGP 9.5) both stained the same structures, namely single fibres, nerve bundles, nerves surrounding vessels and innervating muscles and glands (if present in the section), as well as Merkel cells. Also with these two markers endorgan-like structures were seen. No clear innervation of the epithelium could be observed with the markers used. No methionine-enkephalin (ENK) or synaptophysin (SYN) immunoreactive material was found.

Biochemical correlates to cortical dysplasia, gliosis, and astrocytoma infiltration in human epileptogenic cortex

The study provides detailed biochemical correlates to the common histopathological diagnoses in epilepsy. A dot immunobinding procedure was used for quantification of NSE, GFA, S-100, NCAM, NF 68 and NF 200. The material consisted of samples from 48 patients either selected for surgical treatment of partial epilepsy or for disorders not related to epilepsy. The histopathological diagnosis of the epileptic cases was: MCD (mild cortical dysplasia, microdysgenesis), gliosis, astrocytoma, ganglioglioma, oligodendroglioma and single cases. The concentration in non-epileptic white matter, in per cent of that in grey matter was: NSE, 85; GFA, 175; S-100, 117; NCAM, 43; NF 68,227 and NF 200, 173. The concentration of NSE as well as of GFA was close to normal in the specimens of the MCD and gliosis groups and of one subgroup of the astrocytomas. There was a striking inverse relationship of the GFA vs the NSE concentrations in the whole material. The concentrations of S-100 showed no such inverse relationship to NSE levels. In all the epileptic groups, total NCAM was lower than 50% of that of the non-epileptic group. The mean NF 68 and NF 200 concentration in the gliosis and astrocytoma groups was 75% of that of the non-epileptic group while the corresponding value for the MCD group was 50%. There was a positive correlation of immunochemically determined GFA and the histopathological gliosis score in the samples of epileptogenic cortex. There was no correlation between the concentration of GFA in the samples and the duration of epilepsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Distinction of two different classes of small-cell lung cancer cell lines by enzymatically inactive neuron-specific enolase

Neuron specific enolase (NSE) is widely used as a neuro-endocrine marker. However the presence of NSE in many non-neuroendocrine tissues has raised questions on the specificity of NSE. We have investigated NSE immunoreactivity (NSA-ag), gamma-enolase activity and total enolase activity in small cell lung cancer (SCLC) cell lines. During well-controlled exponential growth comparison of NSE-ag content and gamma-enolase activity with the doubling-time (Td) and NSE-ag content with gamma-enolase and total enolase activity led to a clear distinction of two types of cell line: variant cell lines plus part of the classic cell lines (type I) and the remaining classic cell lines (type II). The distinction was based upon both an abrupt 6-fold increase of gamma-enolase activity and an 18-fold increase of NSE-ag, which for the larger part was enzymatically inactive. Within each group the increase of NSE-ag content was significantly correlated with the increase of gamma-enolase activity and both NSE-ag content and gamma-enolase activity increased linearly with Td. It is concluded that gamma-enolase seems to be associated with the regulation of growth rate and that a compound with the gamma-enolase antigen but without enzyme activity can distinguish two different classes of SCLC cell lines. Furthermore the demonstration that NSE-ag can represent the active enzyme as well as an enzymatically inactive compound may explain why a controversy about neuron- or non-specificity of NSE exists.

Cloning of cDNAs encoding human S-100 alpha and beta subunits and their differential expression in human tumor cell lines

We isolated nearly full-length clones of S-100 alpha and beta subunit cDNAs from a human brain cDNA library. The alpha subunit cDNA was 579 bp long and contained 99 bp of 5'-noncoding region, 282 bp of coding region, and 198 bp of 3'-noncoding region. The beta subunit cDNA was 743 bp long and contained 57 bp of 5'-noncoding region, 276 bp of coding region, and 410 bp of 3'-noncoding region. An amino acid sequence comparison between human and bovine alpha subunits and between human and rat beta subunits showed that both subunits were nearly entirely conserved. The amino acid sequences of human alpha and beta subunits were conserved at both Ca(2+)-binding domains. Northern blot analysis of brain RNA showed that human alpha and beta subunit cDNA probes discriminated between alpha and beta subunit mRNAs. By using these subunit-specific cDNA probes, it was demonstrated that alpha and beta subunit mRNAs were expressed in different manners among tumor cell lines: beta was detected in melanoma and some glioma cell lines, while alpha was detected only in a melanoma cell line. Southern blot analysis showed that there were no major deletions and rearrangements of alpha and beta subunit genes in these cell lines, regardless of the level of alpha and beta subunit expression, suggesting that the expression of these subunits may be regulated at the transcriptional or RNA stability level.

Clonal chromosome abnormalities and in vitro growth characteristics of classical and cellular schwannomas

Cytogenetic analysis was performed on 12 schwannomas, 10 classical and two of the cellular type. Electron microscopic examination of cultured cells from two classical and two cellular schwannomas revealed features compatible with a Schwann cell differentiation. Immunohistochemical analysis of the cultures demonstrated immunoreactivity for S-100 protein in 6 of 6 cases and for vimentin in 2 of 2 cases of classical schwannoma, thus further supporting the authenticity of the cultured cells. Cultured cells from one cellular schwannoma also exhibited immunoreactivity for glial fibrillary acid protein (GFAP). Cytogenetic analysis of the 12 tumors revealed clonal abnormalities in 10 of the cases. In the majority of tumors, cells with a normal karyotype coexisted with different abnormal clones and sporadic deviations. Numerical changes predominated and were found in all tumors, while structural rearrangements were detected in eight tumors. The most common abnormality was clonal or sporadic loss of chromosome 22, which was found in all cases. Other clonal abnormalities included loss of one sex chromosome found in five cases, -15 found in three cases, and -12, +5, +7, +20 found in two cases each. These results provide further evidence in support of a role for loss of chromosome 22 in the pathogenesis of schwannomas. Our findings also indicate that there exist several different evolutionary pathways for schwannomas, and that some of these are shared by several other types of benign and malignant tumors of the nervous system.

Oligodendrogliomas: a clinical, histological, immunocytochemical and lectin-binding study

We have studied 27 oligodendrogliomas with a panel of antibodies (vimentin, GFAP, S-100 protein, myelin basic protein, CAM 5.2) and of lectins (WGA, Con A, PNA, RCA, DBA, SBA) to different glycoproteins. There were 16 well-differentiated tumours, including one gliofibrillary and 11 anaplastic oligodendrogliomas, three of which were gliofibrillary. Four cases showed positivity for vimentin, three of which were anaplastic tumours. Fifteen cases were positive for S-100 protein (nine well-differentiated and six anaplastic tumours) and 13 contained GFAP-positive cells (three well-differentiated and 10 anaplastic tumours). WGA binding was positive in 75% of well-differentiated and 63% of anaplastic oligodendrogliomas, the corresponding figures were 50% and 45% for PNA, 37% and 81% for Con-A and 25% and 54% for RCA. On the basis of the results with lectin binding, we believe that there are changes in the spectrum of tumour cell-associated lectin-like proteins during malignant transformation. Our observations also suggest that the pattern of lectin expression can undergo substantial changes in the course of differentiation.

Immunohistochemical study on the distribution of alpha and beta subunits of S-100 protein in brain tumors

The immunohistochemical distribution of alpha and beta subunits of S-100 protein (S-100 alpha, S-100 beta, respectively) in 138 cases of human brain tumors was investigated by the avidin-biotin immunoperoxidase method. Brain tumors can be divided into four groups: group 1 [S-100 alpha (+) and/or S-100 beta (+)]; astrocytoma, glioblastoma, ependymoma, subependymoma, oligodendroglioma, choroid plexus papilloma, gangliocytoma, meningioma, chordoma, malignant melanoma. Group 2 [S-100 alpha (+) and S-100 beta (-)]; pineoblastoma, pituitary adenoma, craniopharyngioma, rhabdomyosarcoma. Group 3 [S-100 alpha (-) and S-100 beta (+)]; acoustic Schwannoma. Group 4 [S-100 alpha (-) and S-100 beta (-)]; medulloblastoma malignant lymphoma, germinoma. The S-100 beta immunoreactivity pattern in brain tumors was similar to those obtained using conventional anti-S-100 protein sera. In the first group of brain tumors both the number of positively stained tumor cells and the staining intensity were generally greater for S-100 beta than for S-100 alpha with a few exceptions including one gemistocytic astrocytoma, one subependymoma, one malignant melanoma, and some cases of glioblastomas. As to the relationship between malignancy and S-100 protein in glioma, S-100 beta immunoreactivity decreased according to degree of malignancy, while that of S-100 alpha varied, suggesting a heterogeneity of tumor cells in glioblastomas. Immunostaining for S-100 alpha and S-100 beta might become a useful diagnostic procedure in brain tumors and may give us more detailed and precise data of S-100 protein in brain tumors.

Lipocortin-1 immunoreactivity in central and peripheral nervous system glial tumors

We examined the cellular distribution of lipocortin-1 (L-1), a major physiologic substrate for the epidermal growth factor receptor/kinase, in 122 central nervous system (CNS) and peripheral nervous system (PNS) neoplasms using the peroxidase-antiperoxidase technique with a polyclonal antibody specific for L-1. Extensive L-1 immunoreactivity was demonstrated in many CNS tumors; in 11 of 21 glioblastoma multiformes, in five of 12 anaplastic astrocytomas, and in five of 14 astrocytomas. Significant numbers of immunoreactive ependymocytes or astrocytes were also seen in six of 13 ependymomas. In contrast, no immunostaining was detected in the oligodendrocytes in any of ten oligodendrogliomas. PNS tumors, found in two of five malignant nerve sheath tumors, 13 of 15 schwannomas, 13 of 17 neurofibromas, and 14 of 15 traumatic neuromas, also contained considerable L-1 immunoreactivity in Schwann cells or mast cells. These findings raise the possibility that L-1 may participate in the proliferation or subsequent differentiation of neoplastic astrocytes, ependymocytes, and Schwann cells.

An immunohistological study of 66 ependymomas

Sixty-six ependymomas were examined immunohistologically to determine their distribution of glial fibrillary acidic proteins, S-100 protein and vimentin. The neoplasms were subdivided into four groups: (1) ependymomas from the cauda equina, predominantly of the myxopapillary type; (2) benign ependymomas; (3) malignant ependymomas; and (4) ependymoblastomas. Marked differences in antigen reactivity were observed between each group. The intensity of the reaction with the three antibodies was strongest in malignant ependymomas. Ependymomas from the cauda equina showed a patchy distribution of positivity for the three antigens in cells surrounding blood vessels but there was no staining of collagenous septa or the myxoid areas. In ependymoblastomas, the cells of the rosettes were negative for glial fibrillary acidic protein, but there was focal positivity for vimentin and S-100. Other areas showed tumour cells containing moderate amounts of vimentin and small amounts of S-100, and a few bands of filaments positive for glial fibrillary acidic protein. The cytogenetic and biological implications of these findings are discussed.

S-100 immunoreactivity in primary and metastatic carcinoma of the breast: a potential source of error in immunodiagnosis

Immunoreactivity for S-100 protein, typically a marker for malignant melanoma and neural-derived tumors, was observed in neoplastic cells of 57 of 68 cases (84%) of formalin-fixed, paraffin-embedded primary and/or metastatic carcinoma of the breast of various histologic types. The extent of S-100 immunoreactivity varied, with only a minor proportion of positive tumor cells noted in some cases. An awareness of this staining profile for S-100 protein, particularly in metastatic poorly differentiated neoplasms with unknown primaries, is imperative for accurate immunohistochemical interpretation. Using a panel of reagents which includes antibodies to keratin proteins and epithelial membrane antigen, the epithelial nature of S-100-positive carcinomas may be readily defined. Tumor cells in all cases of primary and metastatic carcinoma of the breast evaluated in this study exhibited strong staining for both of these tissue markers. To preclude misinterpretation of tumor type due to anomalous staining patterns for a specific antibody, eg, S-100 protein, a panel of antibodies is recommended for assessment of metastatic poorly differentiated tumors.

Ependymoblastoma: a histological, immunohistological and ultrastructural study of five cases

Five ependymoblastomas were studied by means of routine histological techniques, immunohistology and electron microscopy. The tumours were characterized histologically by medium sized, poorly differentiated cells with round or oval nuclei frequently in mitosis and by ependymoblastic rosettes. Reactions for cytokeratin and neurofilament were negative and tubular material positive for glial fibrillary acidic protein was scanty. All five tumors demonstrated positivity for vimentin and S-100 protein. Electron microscopy showed poorly differentiated cells with high nucleo-cytoplasmic ratio and scanty cytoplasmic organelles. Sparse rosettes were present and the cells were united by junctional complexes. Frequent rudimentary or incomplete cilia, a few basal bodies and a few short intercellular glial-like filaments were seen. Features differentiating ependymomas and anaplastic ependymomas from ependymoblastomas are discussed and the need for a definite category separating ependymoblastomas from the former tumours is emphasized.

An immunocytochemical demonstration of calcineurin in human nerve cell tumors. A comparison with neuron-specific enolase and glial fibrillary acidic protein

Human central and peripheral nerve cell tumors were examined in detail using antibodies to calcineurin, glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE). Forty-eight formalin-fixed and paraffin-embedded specimens of human neuronal tumors, including 27 medulloblastomas, were examined. Calcineurin-positive cells were found in all peripheral nerve cell tumors and the two gangliogliomas, whereas 20 of the 27 medulloblastomas and one of the two cerebral neuroblastomas did not contain calcineurin-positive cells. Differentiation of cells along the neuronal lines was positively correlated with calcineurin immunoreactivity. NSE-positive cells were found in all of the tumors with the exception of the one cerebral neuroblastoma. NSE immunoreactivity was not invariably consistent with calcineurin immunoreactivity and non-neuronal cells were often positive. Calcineurin-positive cells were all devoid of GFAP, but NSE-positive cells expressed GFAP in some tumors. GFAP-immunoreactive cells were found only in central nerve cell tumors, and not in peripheral tumors. In addition, GFAP-positive cells in some tumors such as retinoblastoma and medulloblastoma morphologically revealed not only neoplastic but also reactive astrocytic features.

Immunocytochemistry of intracranial meningiomas

Fifty meningiomas of four major histological types have been examined by immunocytochemical methods applied to formalin fixed paraffin embedded material and using readily available commercial antisera. The expression of GFAP, S100, NSE, vimentin, cytokeratin, fibronectin and desmoplakin was investigated. The majority of tumours contained NSE (86%) and S100 (78%), and all irrespective of histological type, contained vimentin and fibronectin. The epithelial marker cytokeratin was found in 56% of cases, but showed only focal expression. The relevance of these findings to histogenesis and metabolism is discussed and it is suggested that intermediate filament typing provides valuable information on meningiomas structure and function. The possible role of NSE and S100 in meningeal neoplasm is discussed.

S-100 protein and neuron-specific enolase in cerebrospinal fluid and serum: markers of cell damage in human central nervous system

The development of a radioimmunoassay for S-100 protein is described. This method was used in combination with a recently developed radioimmunoassay for neuron-specific enolase in cerebrospinal fluid and serum from 47 patients with cerebral infarction, transient ischemic attack, intracerebral hemorrhage, subarachnoid hemorrhage, and head injury. In cerebrospinal fluid, increased concentrations of both S-100 and neuron-specific enolase were found after large infarcts, whereas after small infarcts and transient ischemic attacks, only neuron-specific enolase increased. The increased concentrations of S-100 and/or neuron-specific enolase were noted 18 hours to 4 days after cerebral infarction and transient ischemic attacks. Cerebrospinal fluid concentrations of these proteins also reflected the severity of the disease in patients with intracerebral hematoma, subarachnoid hemorrhage, or head injury. Temporal changes in serum S-100 and neuron-specific enolase concentrations reflected the clinical course in 4 patients. In stroke patients, the S-100 and neuron-specific enolase concentrations may reflect the extent of brain damage and could be useful in selecting patients with major stroke for more aggressive treatment during the acute phase.

Localization of neuron-specific (gamma gamma) enolase in proliferating (supportive and neoplastic) Schwann cells. An immunohisto- and electron-immunocyto-chemical study of ganglioneuroblastoma and schwannomas

Neuron-specific (gamma gamma) enolase, a glycolytic enzyme used as a relatively specific marker for normal neurons and neuroendocrine cells, has recently been found in a variety of neoplastic cells and in reactive astrocytes. Its localization was investigated by immunohisto- and electron-immunocyto-chemistry, in the proliferating supportive Schwann cells of a peripheral ganglioneuroblastoma and in the neoplastic Schwann cells of four acoustic tumours. By light microscopy, the neoplastic Schwann cells showed moderate uneven diffuse immunopositivity for enolase. By electron-immunocytochemistry, both types of Schwann cells demonstrated immunopositivity discretely limited to their cell surface membranes. The neoplastic ganglion cells and axons of the ganglioneuroblastoma and the normal neurons and axons included in the schwannomas were, as expected, intensely immunopositive. The visualization of gamma gamma enolase on the cell surface membranes of both neoplastic and non-neoplastic proliferating Schwann cells suggests that increased glycolytic activity may occur on the surface of these proliferating cells irrespective of the nature of the proliferation.

Granular cell tumor of the orbit and ocular adnexae

Although granular cell tumor (GCT) has been a distinct pathological entity since 1926, confusion and controversy have long existed regarding the nature and histogenesis of the tumor. Twenty-five cases of granular cell tumor involving the orbit and ocular adnexae previously reported in the ophthalmic literature, are reviewed and six additional cases are reported. The histopathological and immunohistochemical characteristics of granular cell tumors in this uncommon location are discussed and their probable origin from Schwann cells is also considered.

Differential expression of glial- and neuronal-associated antigens in human tumors of the central and peripheral nervous system

The immunoreactivity of a panel of poly- and monoclonal antibodies raised against different glial and neuronal antigens was investigated in paraffin-embedded specimens of 116 human tumors of the central and peripheral nervous system. We used antibodies against the HNK-1 epitope, which is shared between natural killer cells and the nervous system, glial fibrillary acidic protein (GFAP), vimentin, neurofilaments, S-100 protein, neuron-specific enolase (NSE) and myelin basic protein (MBP). HNK-1 immunoreactivity was detectable in nearly all neuroectodermal tumors. Especially in those derived from the neuroepithelium, which include the various types of gliomas, we observed a strong staining with this antibody. The only exceptions were the choroid plexus papillomas and individual ependymomas. In tumors derived from the neural crest HNK-1 reactivity was more variable and less intense. In other tumors of the nervous system HNK-1 was not detectable, except for two out of four malignant lymphomas. In addition to its reactivity with human lymphocytes HNK-1, therefore, seems to be a useful 'marker' for neurogenic tumors in general. GFAP expression was prominent in all astrocytomas and the astrocytic cells within mixed gliomas and gangliogliomas. Immunoreactivity was more variable in glioblastomas and ependymomas, while only isolated GFAP-positive cells were present in oligodendrogliomas, medulloblastomas, one plexus papilloma, and some neurinomas. Vimentin immunoreactivity was found in tumor cells of nearly all tumors of the central nervous system with the exception of oligodendrogliomas, most plexus papillomas, neuronal tumors and most medulloblastomas.

Selective localization of gamma-enolase in stromal cells of cerebellar hemangioblastomas

Three cases of cerebellar hemangioblastoma were studied using the immunoperoxidase technique to localize gamma-enolase, also known as neuron-specific enolase. The stromal cells demonstrated positive staining for gamma-enolase, while endothelial cells and pericytes showed no reactivity. Two vascular lesions, an angiosarcoma and a cutaneous angioma, were studied and found to be nonreactive for gamma-enolase. All tumors were also tested for factor VIII/von Willebrand factor, glial fibrillary acidic protein, and the S-100 protein. The lack of expression of gamma-enolase in endothelial cells of hemangioblastomas demonstrates a clear antigenic distinction from neighboring gamma-enolase-positive stromal cells. The significance of this finding and its implications for stromal cell histogenesis are discussed.

Antineuron specific enolase staining reactions in sarcomas and carcinomas: its lack of neuroendocrine specificity

A commercially available polyclonal antiserum (Dakopatts) raised against bovine neuron specific enolase (NSE) was reacted with 197 sarcomas, 32 carcinomas, 11 carcinoid tumours and 20 malignant melanomas to assess its specificity for neuroendocrine tumours. All the tumours had been fixed in formalin and embedded in paraffin. Positive tumour cells were found in two of 11 squamous cell carcinomas, one of 11 adenocarcinomas, 10 of 10 oat cell carcinomas, 11 of 11 carcinoid tumours, 16 of 20 malignant melanomas, four of seven clear cell sarcomas, nine of 25 leiomyosarcomas, four of 22 rhabdomyosarcomas, one of seven angiosarcomas and one of 20 synovial sarcomas.

Electron-immunocytochemical localization of neuron-specific enolase in cytoplasm and on membranes of primary and metastatic cerebral tumours and on glial filaments of glioma cells

A series of primary and metastatic human brain tumours was evaluated immunocytochemically for the electron microscopic localization of neuron-specific enolase (NSE). All contained cells which, regardless of the cell type, demonstrated an irregular distribution of NSE in their cytoplasm and on membranes. This was in contrast to the staining pattern in normal central nervous system (CNS) cells which, as previously reported (Vinores et al. 1984b), show only diffuse cytoplasmic staining usually not associated with membranes. In the tumours, the interior of nuclei and the cristae and matrices of mitochondria were consistently negative, as in normal CNS cells. Except in one low-grade fibrillary astrocytoma, the cytoplasmic filaments in neoplastic astrocytes were often, but not invariably, stained for NSE. The fine structural localization of NSE in neoplastic cells suggests that the conversion of 2-D-glycerophosphate to phosphoenolpyruvate by enolase may occur on the membrane and, in the case of astrocytic tumours, on the cytoplasmic filaments as well as in the cytoplasm. When cells which contain only the non-neuronal form of enolase (NNE) transform to neoplastic cells, they may acquire the ability to produce NSE. This presumably enables them to accommodate the increased metabolic demands of neoplasia by allowing them to elude the regulatory controls that are specific for NNE.

S-100 proteins

S-100 is a group of closely related, small, acidic Ca2+-binding proteins (S-100a0, S-100a and S-100b, which are alpha alpha, alpha beta, and beta beta in composition, respectively). S-100 is structurally related to calmodulin and other Ca2+-binding proteins. S-100 is abundant in the brain and is contained in well defined cell types of both neuroectodermal and non-neuroectodermal origin, as well as in their neoplastic counterparts. In the mammalian brain, S-100a and S-100b are confined to glial cells, while S-100a0 is neuronal in localization. Single S-100 isoforms bind Ca2+ with nearly the same affinity. K+ antagonizes the binding of Ca2+ to high affinity sites on S-100. S-100 binds Zn2+ with high affinity. S-100 is found in a soluble and a membrane-bound form and has the ability to interact with artificial and natural membranes. S-100 has no enzymatic activity. S-100 has been involved in several activities including memory processes, regulation of diffusion of monovalent cations across membranes, modulation of the physical state of membranes, regulation of the phosphorylation of several proteins, control of the assembly-disassembly of microtubules. Some of these effects are strictly Ca2+-dependent, while other are not. S-100 is being secreted or released to the extracellular space. In some cases, this event is hormonally regulated. Several S-100 binding proteins are being described.

Normal and malignant neural cells: a comprehensive survey of human and murine nervous system markers

Tumor-associated neural markers are finding increased application in diagnostic histopathology and in the development of brain tumor therapy. The major cell-type-specific markers and monoclonal antibodies that identify murine and human neural cells are reviewed in this study. Monoclonal antibodies, raised against fetal and adult neural tissue, neuroectodermal tumor tissue, or cell line immunogens which recognize epitopes on brain tumors are comprehensively described including antigens common to the nervous, hematopoietic, and immune systems. The clinical application of neural cell markers and monoclonal antibodies for the diagnosis, localization, and treatment of neuroectodermal tumors is reviewed.

An immunohistochemical study of glial and neuronal markers in primary neoplasms of the central nervous system

Paraffin-embedded tissues from 56 primary neoplasms of the central nervous system and seven cases of non-neoplastic reactive astrocytosis were examined by immunoperoxidase techniques on serial sections using monoclonal antibodies to glial fibrillary acidic protein (GFAP) and the 68 kDa neurofilament subunit and monospecific polyclonal antibodies to alpha- and gamma-enolase. gamma-Enolase was present in all neoplasms of neuronal origin, but was also present in anaplastic gliomas (particularly in giant cells), in some well-differentiated astrocytomas and reactive astrocytes. The cells containing gamma-enolase in these cases appeared morphologically identical to those containing alpha-enolase and GFAP in adjacent serial sections. No relationship was found between gamma-enolase immunoreactivity and cellular anaplasia in the gliomas studied. Subependymal neoplasms from patients with tuberose sclerosis exhibited evidence of both astrocytic and neuronal differentiation, sometimes in morphologically distinct cell populations, consistent with their suggested origin from a primitive cell line.

S-100 protein and calmodulin levels in cerebrospinal fluid after subarachnoid hemorrhage

The levels of two calcium-binding proteins, S-100 protein and calmodulin, were measured serially in the cerebrospinal fluid (CSF) of patients after subarachnoid hemorrhage (SAH) and aneurysm surgery. These two proteins have a similar molecular structure and are highly concentrated in the central nervous system (CNS). The levels of S-100 protein found in the earliest postoperative CSF samples correlated with the preoperative SAH grades. High S-100 protein levels in the CSF were found in patients with poor SAH grades. Moreover, the prognosis of the patients correlated with the S-100 protein levels in the CSF samples taken during the immediate postoperative period and with the daily changes of the S-100 protein levels. Severe diffuse cerebral vasospasm was followed by a sharp S-100 protein increase. These results suggest that S-100 protein levels in the CSF provide a useful index of organic damage in the CNS, and furthermore that S-100 protein levels and their changes may have prognostic value for patients after SAH. On the other hand, there was a lack of correlation between the calmodulin levels and the preoperative grade or outcome. It would be inappropriate, however, to speculate from the results of this study that these calcium-binding proteins in the CSF play any causative role in pathological processes such as cerebral vasospasm or brain ischemia after SAH, since changes in the levels of these proteins followed the onset of clinical signs of deterioration.

Simultaneous expression of glial fibrillary acidic (GFA) protein and neuron-specific enolase (NSE) by the same reactive or neoplastic astrocytes

In normal cells of the central nervous system (CNS), glial fibrillary acidic (GFA) protein is demonstrable by immunohistochemistry in fibrillated astrocytes, and neuron-specific enolase (NSE) in neurons and their processes. However, it has been shown that NSE may also be expressed in reactive astrocytes and in various neoplastic cells of non-neuronal origin, including those of astrocytomas and glioblastomas. In the present study, a double-labelling technique using immunoperoxidase (PAP) and immunofluorescence (FITC) was employed to determine whether GFA protein and NSE could be expressed simultaneously by the same cell. This was found to be the case in some, but not in all reactive astrocytes in the human brain. In glial tumours, many of the neoplastic cells in the glioblastomas and astrocytomas examined demonstrated either GFA protein or NSE, but usually not both. However, occasional neoplastic cells in those gliomas were found to show both proteins. Because of the relatively low sensitivity of the FITC technique, the percentage of cells expressing both proteins could not be determined, but it is clearly possible for a single reactive or neoplastic astrocyte to demonstrate both GFA protein and NSE.

Myxopapillary ependymoma. A clinicopathologic and immunocytochemical study of 77 cases

The study involved 77 myxopapillary ependymomas of the spinal cord encountered during a 60-year period (1924-1983). This variant of ependymoma was, with few exceptions, limited to the lumbosacral region, particularly the filum terminale. The male:female ratio was 1.7:1, and the mean age at diagnosis was 36.4 years (range, 6-82); at presentation, 15 (19%) of the patients were in the first two decades of life. The duration of symptoms ranged from 1 month to 30 years; the most frequent complaint was low-back pain, and eight patients had undergone prior "disc surgery." Generally, myelographic block was disclosed. Preoperative cerebrospinal fluid protein levels averaged 2462 mg/dl. Myxopapillary ependymomas are slow-growing tumors that show no significant tendency to histologic dedifferentiation. Despite some variation in cytologic features and the presence of atypia and modest mitotic activity in most cases, the gross characteristics of the tumors appear to be of greater prognostic significance than the histologic features. Tumors that were encapsulated (25%) and amenable to intact, total surgical removal had a recurrence rate of 10%, whereas those that were removed either piecemeal (34%) or subtotally (41%) had recurrence rates of 19%. Overall survival, however, was more closely related to residual disease; total removal of tumor, whether intact (encapsulated) or piecemeal, resulted in longer survival (19 years) than did subtotal resection (14 years). Patients who died (6.5%) did so after a prolonged course marked by multiple recurrences. Radiotherapy may be of particular benefit to patients whose tumors are not amenable to intact total removal.

Applications of monoclonal antibodies in the diagnosis and treatment of primary brain tumors

The development of monoclonal antibodies has resulted in marked expansion in understanding the central nervous system (CNS). This has been especially true in the study of human neuroectodermal tumors where monoclonal antibodies have been used as physiological probes to define and characterize human neuroectodermal tumor-associated antigens. Utilizing monoclonal antibodies, neuroectodermal tumor-associated antigens have been described in four broad categories; biochemically defined markers, shared nervous system-lymphoid cell markers, shared neuroectodermal-oncofetal markers, and putative restricted tumor markers. Preliminary data have demonstrated the ability to localize animal and human tumors in vitro, ex vivo, and in vivo. Early application of monoclonal antibody technology to neuroimmunology and neuro-oncology has resulted in a new awareness of the complex relationships that exist within the CNS. Their specificity and reproducibility may provide the means to qualitatively and quantitatively define the phenotypic heterogeneity of human neuroectodermal tumors. Potentially, monoclonal antibodies, alone or as carriers of radionuclides, drugs, or toxins, may allow successful diagnosis and treatment of human neuroectodermal tumors.

Immunohistological demonstration of S-100 protein in the cutaneous nervous system

S-100 protein, isolated from mammalian brain, has widely been used for immunohistochemical marker of the glia cells and the cells derived from the neural crest. In the present study, we made anti S-100 protein antibody and studied the immunoreactive distribution of S-100 protein in the cutaneous nervous system. Albino rabbits were immunized with S-100 protein and complete Freund adjuvant, and antiserum was purified by ion-exchange chromatography. Formalin-fixed normal human skin and sciatic nerve of rat were examined by the PAP method. S-100 protein was detected in Schwann cells of sciatic nerve of rat and cutaneous nerve bundles of human skin specimens. Meissner corpuscles and inner core cells of Pacinian corpuscles of human skin were S-100 protein positive. These findings suggest that the staining of S-100 protein with PAP method is a simple and reliable method to demonstrate the cutaneous nervous system. Also, lamellar cells of Meissner corpuscles and inner core cells of Pacinian corpuscles are indicated to be Schwann cell origin.

Granular cell tumor of the lower lid: histological and immunohistochemical studies

Histological and immunohistochemical studies of a granular cell tumor involving the lower lid are described. Histological examination showed it to have typical features of a granular cell tumor. Nervous-system-specific protein (S-100 protein) was detected in both the nuclei and cytoplasm of granular cells using the peroxidase-anti-peroxidase method. This result further supports the concept of the neurogenic origin of granular cell tumors.

Enolase distribution in human brain tumors, retinoblastomas and pituitary adenomas

The cellular localization of alpha-, beta- and gamma-subunits of enolase isoenzyme was studied immunohistochemically in various human brain tumors, retinoblastomas and pituitary adenomas (total, 91 cases). The alpha-subunit was found in almost all brain tumors except in medulloblastoma cases. A case of medullomyoblastoma contained beta-subunit-positive myoblastic cells, which was also positive for human myoglobin. The gamma-subunit was frequently observed in medulloblastomas, retinoblastomas and pituitary adenomas. However, gamma-subunit was also present in some non-neuronal brain tumors such as astrocytomas and oligodendrogliomas. Enzyme immunoassay technique also confirmed the presence of gamma-subunit in a medulloblastoma and two retinoblastomas.

Immunohistochemistry of central nervous system tumors. Its contributions to neurosurgical diagnosis

Immunofluorescence and immunoperoxidase (peroxidase-antiperoxidase, PAP) techniques for the demonstration of neural and non-neural cell markers are contributing greatly to increase the diagnostic accuracy of difficult tumors of the central nervous system. Well characterized nervous system markers include glial fibrillary acidic (GFA) protein, the three protein subunits of neurofilaments, neuron-specific enolase (NSE), myelin basic protein, and S-100 protein. The most important and reliable of these is GFA protein, which is widely in use for the immunohistochemical diagnosis of tumors of the glioma group. Its many practical applications are reviewed and illustrated. Other neural markers, in particular the specificity of NSE and S-100 protein, need to be critically evaluated. Problems related to the immunohistochemical diagnosis of central neuroepithelial tumors of putative neuroblastic origin remain complex and still need to be resolved. Non-neural markers, such as vimentin, desmin, cytokeratins, Factor VIII, alpha-fetoprotein, human chorionic gonadotropin, and immunoglobulins have well defined, although more restricted, applications in surgical neuropathology.

Dermal nerve sheath myxoma. A light and electron microscopic, histochemical and immunohistochemical study

Two cases of dermal nerve sheath myxoma have been examined by light and electron microscopy, and by immunohistochemical and histochemical methods. The nomenclature of this tumor has been debated, and the histogenesis unsettled. Light microscopically, the lobulated myxoid tumors were generally composed of spindle-shaped and stellate tumor cells in an abundant matrix of mucosubstances. Ultrastructural features indicated an origin from the peripheral nerve sheath; among the pertinent findings were a single or duplicated external lamina investing the cells, desmosome-like junctions, cytoplasmic microfilaments and myelin figures, and interdigitating cytoplasmic processes. S-100 protein was demonstrated by means of the immunoperoxidase technique within both tumors, further supporting this origin. The histochemical analysis of the mucosubstance showed the presence of sulphated glucosaminoglycans. The name dermal nerve sheath myxoma, suggested by Harkin and Reed, is recommended.

Granular cell tumour of the mammary gland simulating malignancy. A report on two cases with light microscopy, transmission electron microscopy and immunohistochemical investigation

Primary granular cell tumours of the breast in 35 and 55 year old women were studied by light microscopy, transmission electron microscopy and immunohistochemistry. Light and electron microscopy revealed a neural origin of the tumours and this was further substantiated by immunohistochemical studies, with positive S-100 protein reaction and negative reactions for surface heavy and light chains, CEA, alfa-1-antitrypsin, muramidase and GFA-protein. Granular cell tumour of the mammary gland is a very rare tumour. Clinically it sometimes simulates carcinoma because of its fibrous consistency, fixation to pectoral fascia and skin retraction. The diagnosis of granular cell tumour should be included in the differential diagnosis of carcinoma of the breast. The granular cell tumour is derived from neuro-ectodermal tissue. Whether it represents a neurogenic cell-confined metabolic disturbance with lysosomal activation, or a true neoplasm remains to be elucidated.

Subependymal giant cell astrocytoma. Significance and possible cytogenetic implications of an immunohistochemical study

Twenty-two cases of subependymal giant cell astrocytoma (SGCA), five of which associated with tuberous sclerosis, were reviewed by conventional neurohistological stains and by peroxidase-antiperoxidase (PAP) immunohistochemistry for glial fibrillary acidic (GFA) protein, the 68 Kd neurofilament subunit (68 Kd-NF), and neuron-specific enolase (NSE). Neurohistological stains confirmed the presence of PTAH-positive fibrils and the absence of Nissl bodies and of neurites originating from the tumor cells. GFA protein-positive cells were present in all tumors not associated with tuberous sclerosis. However, the number of positive cells in each tumor was highly variable. GFA protein-positive cells were rare in the two SGCA accompanying tuberous sclerosis and absent in the remaining three. Neurohistological stains showed no differences between GFA protein-positive and negative cells. 68 Kd-NF-positive cells were found in six tumors. In one tumor, associated with tuberous sclerosis, it was present in the large ganglion-like cells only. NSE-positive cells were found in 13 of 18 tumors examined, including four of the five SGCA associated with tuberous sclerosis. The significance of NSE-positivity in central neuroepithelial neoplasms in respect of their possible neuronal origin remains open. This study suggests that the SGCA, especially those associated with tuberous sclerosis, include cells that are apparently unable to express GFA protein. Some of the tumor cells express the 68 Kd-NF, but this expression falls short of the complete expression of neuronal differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Clear-cell sarcoma of tendons and aponeuroses. An immunohistochemical and electron microscopic analysis indicating neural crest origin

A clinico-pathological, light microscopic and immunohistochemical study of 15 clear-cell sarcomas, with an ultrastructural analysis of 6 of the tumors, is presented. The tumors showed a strong predilection for tendons and aponeuroses of the extremities in predominantly young and middle-aged people. The clinical setting, course and light microscopic appearance agree well with the original description by Enzinger (1965). Nine of the 15 patients developed metastases, most of them including lymph nodes, and 8 of the patients had died at the time of follow-up (median follow-up time 4.8 years). Reducing pigment was demonstrated within the cells of 2 tumors. Ultrastructurally the 6 tumors studied had a uniform appearance with characteristically rounded or oval tumor cells with a single nucleus containing one or two very prominent nucleoli, a light-staining cytoplasm with a moderate amount of organelles and a variable content of glycogen. Polymorphic melanosomes were seen in the cells of one of the tumors. External laminas enclosed groups of tumor cells and invested parts of individual tumor cells. With immunoperoxidase analysis for S-100 protein positive staining was observed in the vast majority of the tumor cells of all 15 clear-cell sarcomas. Metastases appearing in 9 of the 15 cases showed positive staining for S-100 protein. There was a strong staining of the cytoplasm and generally a weak and varying staining of nuclei. The immunohistochemical and electron microscopic findings indicate that clear-cell sarcoma is a homogenous entity among soft tissue sarcomas, of probable neural crest derivation.

Chemistry and biology of the S-100 protein

The S-100 protein is specific for the nervous system and, being present in all vertebrates, shows a high degree of stability of structure during evolution. In adult animals it is primarily localized to glial elements, although there is some evidence that a small proportion may be present in neuronal nuclei or their plasma membranes. During development it is synthesized rapidly at a relatively late period of differentiation of the nervous system. In glioma cell cultures there is a control mechanism that seems to involve some kind of signal at the external surface of the plasma membrane, possibly specific cell-cell contact, to stimulate S-100 synthesis. All of these biological properties of S-100 suggest that it is connected with some specific essential function that is common to the nervous system of all vertebrates. Several chemical properties of S-100 provide clues to this function. It is an unusually acidic and soluble protein and, in the absence of Ca2+, has no detectable hydrophobic regions accessible to solvent. It is capable of specifically binding Ca2+, a process that causes S-100 to undergo a conformational change that exposes a hydrophobic region to the solvent and stimulates binding of S-100 to membranes. The conformational change and the membrane-binding properties are reversible when Ca2+ is removed and are antagonized by monovalent cations such as K+ and Na+. These chemical properties suggest that S-100 may, as part of its function in the nervous system, be bound to some hydrophobic site, possibly a membrane, and that the extent of this binding is regulated by concentrations of Ca2+, K+ and Na+. If this is true, then it is important, as the next step in working out its function, to discover the exact site where S-100 binds in the nervous system.