Experience with newer central nervous system autoantibodies.

In the last decade, a large number of neuronal cell-surface antibodies have been described which are responsible for a range of neuroimmunological central nervous system disorders. Unlike the paraneoplastic antibodies which target intracellular antigens, these antibodies appear to be pathogenic and hence identification and prompt treatment can make a substantial impact on clinical outcomes of these patients. We review the common antibodies against the ionotropic glutamate receptors (NMDAR, AMPAR), metabotropic glutamate receptors (mGluR1 and mGluR5), voltage-gated potassium channel-complex proteins (LGI1, CASPR2), and other antibodies targeted against glycine receptor, glutamic acid decarboxylase, gamma-amino butyric acid B, dopamine-2-receptor and dipeptidyl-peptidase-like protein 6.

Photolabeling of erythrocyte and adipocyte hexose transporters using a benzophenone derivative of bis(D-mannose).

The benzophenone derivative of 1,3-bis(D-mannos-4-yloxy)-2-propylamine (BB-BMPA) has been tested as an exofacial photoaffinity label for the sugar transport systems of human erythrocytes and rat adipocytes. The half-maximal inhibition constants for the reagent are 971 microM in erythrocytes and 536 microM in basal and 254 microM in insulin-treated adipocytes. The photolabelling of erythrocyte membranes is very specific for the 50 kDa transporter peptide and is completely displaced by D-glucose. The exofacial photoaffinity labelling of adipocytes also shows labelling of a 50 kDa transporter peptide, which is displaced by cytochalasin B, but extensive nonspecific labelling of a 75 kDa plasma membrane peptide occurs. The transporter is labelled in insulin-treated cells but not in basal cells which indicates that this in situ labelling technique selectively reveals only those transporters that visit and are active in the plasma membrane during the labelling period. This also indicates that in basal cells transporters do not turn over rapidly. Subcellular redistribution of transporters after the labelling period has been studied. Following incubation and washing at 37 degrees C in the presence of insulin, 30% of the transporters photolabelled at the plasma membrane are internalised and are found in the light microsome fraction of the cell. The proportion of transporter that is observed to be internalised is much greater than can be accounted for by a contamination of the light microsome fraction by plasma membrane. The labelled 50 kDa transporter peptide in the light microsomes is enriched when compared with the carry-over of the 75 kDa nonspecifically labelled plasma membrane peptide. Thus we have obtained direct evidence for transporter translocation.

Binding of cytochalasin B to trypsin and thermolysin fragments of the human erythrocyte hexose transporter.

The cleavage of the human erythrocyte hexose transporter by the proteinases trypsin and thermolysin has been studied. When red cell membranes are treated with trypsin, washed and then photolabelled with cytochalasin B, a labelled peak at 18 kDa is obtained. This labelling of the cleaved transporter is D-glucose inhibitable. This probably indicates that the residual 36 kDa portion of the transporter is not required for binding of ligands. Extensive cleavage of the transporter with low concentrations of thermolysin only occurs when transporter is prelabelled with cytochalasin B. This indicates that covalently bound cytochalasin B can cause a conformational change which exposes the thermolysin cleavage site.

Interaction of motor neurone disease plasma with glucose transport.

Abnormal glucose metabolism has been implicated in motor neurone disease (MND) and this was studied by measuring the transport of non-metabolisable glucose analogue, 3-O-methyl-D-glucose in normal erythrocyte at 20 degrees C, pH 7.4, in the presence of plasma from normal controls and patients with MND. The glucose uptake was elevated by 34% in the presence of plasma from MND patients (n = 21) when compared with age matched controls (n = 28; p < 0.001). The uptake of glucose was not influenced by gender or any age dependent variations. The relationship of this effect to glucose under-utilisation in the CNS needs to be explored.

Immunological markers in neurological disorders.

Neurological dysfunction results from vascular, inflammatory, degenerative, neoplastic, metabolic or genetic causes. Of particular interest is a group of neurological symptoms thought to be linked to an underlying tumour, the so-called paraneoplastic syndromes. It is considered to be due to an attempt by the immune system to subjugate the growth of the tumour by triggering an antibody response against the neuronal antigens expressed by the neoplasm. The unfortunate consequence of this is an assault by the immune components on the nervous tissue, thereby rapidly precipitating a variety of neurological deficits. Every level of the nervous system is potentially vulnerable, with the disability being considered as irreversible due to the lack of regenerative capacity of the neurons. This phenomenon is rare, occurring at an approximate frequency of less than 1% of all tumours and often accompanied by the presence of specific high-titre autoantibodies in both the cerebrospinal fluid and blood. This group of antibodies are non-pathogenic markers for paraneoplastic neurological syndromes, which have expanded to almost 20 since the discovery, in 1986, of the first clinically relevant syndrome. More recently, a new generation of antineuronal antibodies against cell surface antigens, having a direct pathogenic role in causing the disease, has emerged to complement the existing repertoire. Neuronal antibodies are useful diagnostic markers of the brain disease and also, in some cases, may reveal an underlying malignancy, thus facilitating faster diagnosis and earlier treatment with consequently better prognosis.