Autophagosome-like vacuole formation in Huntington's disease lymphoblasts

In an effort to clarify cellular abnormalities in Huntington's disease without the confounding factor of gross degeneration and postmortem alterations associated with studies of the brain, we have examined HD patient lymphoblasts. We report pronounced vacuole formation in patients. The vacuoles possess huntingtin remnants and cathepsin B staining, a lysosomal marker, suggesting autophagy. The number and size of vacuoles parallel the number of polyglutamine repeats in patients. Treatment with staurosporine, which augments apoptosis, leads to increased vacuole formation in Huntington's disease cells but does not influence control cells. Our findings provide direct evidence for abnormalities in Huntington's disease tissues outside the brain under basal conditions. Autophagic cellular alterations may be utilized as peripheral markers of Huntington's disease pathology.

Antigliadin antibodies in Huntington's disease

The relevance of gluten sensitivity in sporadic and hereditary ataxia pathogenesis is unclear. The authors found high antigliadin antibody titers in 23 of 52 (44%) patients with Huntington's disease (HD), suggesting a previously unrecognized association between HD and gluten sensitivity. The results further question "gluten ataxia" as a distinct disease entity and raise the possibility that antigliadin antibodies in ataxia and other neurodegenerative diseases may be an epiphenomenon, the mechanisms of which remain to be investigated.

Huntington's disease transgenic mice are resistant to global cerebral ischemia

Excitotoxicity plays a key role in ischemic neuronal death and is also one of the candidate mechanisms contributing to neurodegeneration in Huntington's disease (HD). Unexpectedly we have now found that transgenic mice expressing exon 1 of a mutant human HD gene (R6/1) are protected against global cerebral ischemia (GCI), installed by temporary bilateral occlusion of the carotid arteries. Whereas wild type mice showed a substantial neuronal damage in the hippocampus following 15, 20 and 60 min of GCI, transgenic mice were partially protected after 15 and 20 minutes of hypoxemia. This tolerance to ischemia is not blocked by pretreatment of mice with cycloheximide, an unspecific protein synthesis inhibitor. We conclude that this form of tolerance to ischemia in HD transgenic mice--although somewhat reminiscent of ischemic tolerance after ischemic preconditioning--is therefore independent of short term expression of endogenous neuroprotective proteins.

Geldanamycin activates a heat shock response and inhibits huntingtin aggregation in a cell culture model of Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative disorder with no effective treatment. Geldanamycin is a benzoquinone ansamycin that binds to the heat shock protein Hsp90 and activates a heat shock response in mammalian cells. In this study, we show by using a filter retardation assay and immunofluorescence microscopy that treatment of mammalian cells with geldanamycin at nanomolar concentrations induces the expression of Hsp40, Hsp70 and Hsp90 and inhibits HD exon 1 protein aggregation in a dose-dependent manner. Similar results were obtained by overexpression of Hsp70 and Hsp40 in a separate cell culture model of HD. This is the first demonstration that huntingtin protein aggregation in cells can be suppressed by chemical compounds activating a specific heat shock response. These findings may provide the basis for the development of a novel pharmacotherapy for HD and related glutamine repeat disorders.

Transplanted fetal striatum in Huntington's disease: phenotypic development and lack of pathology

Neural and stem cell transplantation is emerging as a potential treatment for neurodegenerative diseases. Transplantation of specific committed neuroblasts (fetal neurons) to the adult brain provides such scientific exploration of these new potential therapies. Huntington's disease (HD) is a fatal, incurable autosomal dominant (CAG repeat expansion of huntingtin protein) neurodegenerative disorder with primary neuronal pathology within the caudate-putamen (striatum). In a clinical trial of human fetal striatal tissue transplantation, one patient died 18 months after transplantation from cardiovascular disease, and postmortem histological analysis demonstrated surviving transplanted cells with typical morphology of the developing striatum. Selective markers of both striatal projection and interneurons such as dopamine and c-AMP-related phosphoprotein, calretinin, acetylcholinesterase, choline acetyltransferase, tyrosine hydroxylase, calbindin, enkephalin, and substance P showed positive transplant regions clearly innervated by host tyrosine hydroxylase fibers. There was no histological evidence of immune rejection including microglia and macrophages. Notably, neuronal protein aggregates of mutated huntingtin, which is typical HD neuropathology, were not found within the transplanted fetal tissue. Thus, although there is a genetically predetermined process causing neuronal death within the HD striatum, implanted fetal neural cells lacking the mutant HD gene may be able to replace damaged host neurons and reconstitute damaged neuronal connections. This study demonstrates that grafts derived from human fetal striatal tissue can survive, develop, and are unaffected by the disease process, at least for 18 months, after transplantation into a patient with HD.

Degradation of tryptophan in neurodegenerative disorders

In patients with neurodegenerative disorders, namely Alzheimer's disease and Huntington's disease, we compared serum concentrations of tryptophan, kynurenine and the kynurenine per tryptophan ratio with concentrations of soluble immune activation markers. Significantly lower tryptophan concentrations were observed in the patients, and lower tryptophan levels as well as higher kynurenine levels and higher kynurenine per tryptophan ratios correlated with higher concentrations of neopterin, and soluble receptors for TNF and interleukin-2. In both groups of patients tryptophan concentrations correlated inversely with the degree of mental retardation. No such association existed for the duration of the disease. The data show that systemic chronic immune activation in patients with Alzheimer's disease and Huntington's disease is associated with significant degradation of tryptophan, which is most likely due to activation of indoleamine (2,3)-dioxygenase by immunologic stimuli. Further studies will be necessary to investigate a potential role of tryptophan degradation in the pathogenesis of neurodegenerative disorders.

Increased complement biosynthesis by microglia and complement activation on neurons in Huntington's disease

In this study complement activation and biosynthesis have been analysed in the brains of Huntington's disease (HD) (n = 9) and normal (n = 3) individuals. In HD striatum, neurons, myelin and astrocytes were strongly stained with antibodies to C1q, C4, C3, iC3b-neoepitope and C9-neoepitope. In contrast, no staining for complement components was found in the normal striatum. Marked astrogliosis and microgliosis were observed in all HD caudate and the internal capsule samples but not in normal brain. RT-PCR analysis and in-situ hybridisation were carried out to determine whether complement was synthesised locally by activated glial cells. By RT-PCR, we found that complement activators of the classical pathway C1q C chain, C1r, C4, C3, as well as the complement regulators, C1 inhibitor, clusterin, MCP, DAF, CD59, were all expressed constitutively and at much higher level in HD brains compared to normal brain. Complement anaphylatoxin receptor mRNAs (C5a receptor and C3a receptor) were strongly expressed in HD caudate. In general, we found that the level of complement mRNA in normal control brains was from 2 to 5 fold lower compared to HD striatum. Using in-situ hybridisation, we confirmed that C3 mRNA and C9 mRNA were expressed by reactive microglia in HD internal capsule. We propose that complement produced locally by reactive microglia is activated on the membranes of neurons, contributing to neuronal necrosis but also to proinflammatory activities. Complement opsonins (iC3b) and anaphylatoxins (C3a, C5a) may be involved in the recruitment and stimulation of glial cells and phagocytes bearing specific complement receptors.

Activated immune system in patients with Huntington's disease

Abnormalities of immune system compartments were determined in 12 patients with Huntington's disease (eight males, four females; age 42.4+/-11.7 years) and 11 controls (7 males, 4 females; age 47.0+/-12.0). All patients were free from infectious diseases. Serum concentrations of a panel of serum soluble markers of immune activation were investigated, namely neopterin, 55-kDa-type soluble tumor necrosis factor receptor (sTNF-R), interleukin-2-receptor (sIL-2R), kynurenine, tryptophan, immunoglobulins (Ig) A, M and G as well as routine laboratory tests. Compared to controls, we found significantly higher serum levels of IgA (p<0.01), sTNF-R, sIL-2R, neopterin, and complement component C3 (all p<0.05), and serum tryptophan was decreased (p<0.001). Higher concentrations of circulating immune complexes, cardiolipin antibodies, IgM, neopterin and lower tryptophan were associated with loss of cognitive function as assessed by the mini-mental-test. Five patients died within 1 year after measurements were performed. In these patients IgM, circulating immune complexes and neopterin concentrations were higher compared to survivors and serum tryptophan was lower. The data indicate an activation of various immune system compartments in Huntington's disease and that systemic immunological alterations might be important in the course of the disease.

Neuronal cell transplantation for Parkinson's and Huntington's diseases

The brain constitutes a privileged transplantation site. Under appropriate conditions neuronal tissues can survive transplantation into the damaged brain, integrate with the host, and alleviate functional impairments associated with neurological disease. The experimental techniques have been developed to the point of clinical application with demonstrable benefit in Parkinson's disease, and similar applications in Huntington's disease appear to be imminent. Nevertheless, present techniques require use of embryonic/fetal tissues which will limit the availability of donors for the foreseeable future. There is an active search for alternative sources of tissue that are equally effective but more readily available, including engineered cells, expanded stem/precursor cells, and xenografts.

Polyglutamine expansion as a pathological epitope in Huntington's disease and four dominant cerebellar ataxias

A polyglutamine expansion (encoded by a CAG repeat) in specific proteins causes neurodegeneration in Huntington's disease (HD) and four other disorders, by an unknown mechanism thought to involve gain of function or toxicity of the mutated protein. The pathological threshold is 37-40 glutamines in three of these diseases, whereas the corresponding normal proteins contain polymorphic repeats of up to about 35 glutamines. The age of onset of clinical manifestations is inversely correlated to the length of the polyglutamine expansion. Here we report the characterization of a monoclonal antibody that selectively recognizes polyglutamine expansion in the proteins implicated in HD and in spinocerebellar ataxia (SCA) 1 and 3. The intensity of signal depends on the length of the polyglutamine expansion, and the antibody also detects specific pathological proteins expected to contain such expansion, in SCA2 and in autosomal dominant cerebellar ataxia with retinal degeneration, whose genes have not yet been identified.

SMI-32 antibody against non-phosphorylated neurofilaments identifies a subpopulation of cultured cortical neurons hypersensitive to kainate toxicity

SMI-32, an antibody against a non-phosphorylated neurofilament epitope identifies a subpopulation of human cortical neurons preferentially lost in Alzheimer's or Huntington's disease. In murine cortical cultures SMI-32 labeled a small subset of neurons exhibiting enhanced vulnerability to kainate toxicity. Most SMI-32(+) neurons were GABAergic and exhibited kainate-activated Co2+ uptake. Thus expression of Ca2+ permeable AMPA or kainate receptor-gated channels likely underlies the heightened vulnerability of SMI-32(+) cortical neurons to kainate.

Effects of striatal excitotoxicity on huntingtin-like immunoreactivity

The relationship between the specific neuronal loss observed in Huntington's disease and the mutation in the IT15 gene responsible for this disease remains obscure. Using an antipeptide antibody against amino acids 3114-3141 of the human huntington protein, we demonstrate that striatal injection of quinolinic acid in mice induces increased immunoreactivity for huntington in some remaining neurons but not in glial cells. This increase is apparent in both neuronal cell bodies and in cell processes in the white matter six hours after excitotoxic challenge. This finding suggests that huntington may be involved in the response to excitotoxic stress in these neurons.

Normal and expanded Huntington's disease gene alleles produce distinguishable proteins due to translation across the CAG repeat

BACKGROUND

An expanded CAG trinucleotide repeat is the genetic trigger of neuronal degeneration in Huntington's disease (HD), but its mode of action has yet to be discovered. The sequence of the HD gene places the CAG repeat near the 5' end in a region where it may be translated as a variable polyglutamine segment in the protein product, huntingtin.

MATERIALS AND METHODS

Antisera directed at amino acid stretches predicted by the DNA sequence upstream and downstream of the CAG repeat were used in Western blot and immunohistochemical analyses to examine huntingtin expression from the normal and the HD allele in lymphoblastoid cells and postmortem brain tissue.

RESULTS

CAG repeat segments of both normal and expanded HD alleles are indeed translated, as part of a discrete approximately 350-kD protein that is found primarily in the cytosol. The difference in the length of the N-terminal polyglutamine segment is sufficient to distinguish normal and HD huntingtin in a Western blot assay.

CONCLUSIONS

The HD mutation does not eliminate expression of the HD gene but instead produces an altered protein with an expanded polyglutamine stretch near the N terminus. Thus, HD pathogenesis is probably triggered by an effect at the level of huntingtin protein.

Evidence for a preferential loss of enkephalin immunoreactivity in the external globus pallidus in low grade Huntington's disease using high resolution image analysis

Previous studies have shown that in advanced cases of Huntington's disease, enkephalin-immunoreactive striatal projections to the external globus pallidus may be more affected than substance P-containing striatal projections to the inner segment of the pallidum [Reiner A. et al. (1988) Proc. natn. Acad. Sci. U.S.A. 85, 5733-5737]. Other immunohistochemical [Ferrante R. J. et al. (1990) Soc. Neurosci. Abstr. 16, 1120] and neurochemical observations [Storey E. and Beal M.F. (1993) Brain 116, 1201-1222] suggest no difference in the loss of these peptide-containing pathways in Huntington's disease. In view of the potential significance of this issue for understanding the neuropathological process in Huntington's disease, we examined the globus pallidus in control and Huntington's disease brains, using a quantitative approach which involved high resolution image analysis of 7 microns frozen sections to determine the overall density of peptide-immunoreactive terminals. Results showed that in the controls there was no significant difference between the density of enkephalin- and substance P-immunoreactive terminals in the external and internal globus pallidus, respectively. In all Huntington's disease brains, including grade 1 cases, enkephalin-immunoreactive terminals in the external globus pallidus were significantly reduced compared to substance P-positive boutons in the internal segment of the adjacent section. In comparison to controls, enkephalin immunoreactivity in all Huntington's disease cases was significantly lower; substance P-immunoreactive terminals in the internal globus pallidus were significantly lower than controls in some of the grade 2 cases and in the grade 3 cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain extracts containing a Huntington disease antigen inhibit [3H]kainate binding and block synaptosomal amino acid transport

Fractions isolated from mammalian brain which had previously been shown to inhibit the rate of migration of peripheral blood leukocytes taken from Huntington disease cases, and also to inhibit [3H]kainic acid binding, were characterized further. By use of repeated ultrafiltration onto a 1000D MW cutoff filter, and by the isolation and extensive washing of an enriched ammonium sulfate fraction, their activity was shown not to be due to the presence of endogenous glutamate, and to be relatively selective for brain glutamate receptor binding sites. Inhibitory activity at [3H]GABA, 5-[3H]hydroxytryptamine 5HT1 and dopamine D1 or D2 binding sites was much weaker or absent. Factor extracts were also shown to act as non-competitive inhibitors of synaptosomal amino acid transport: increasing concentrations of the factor had no significant effect on the KM for the uptake of either [3H]glutamate or [3H]GABA, but at a final concentration of 66 micrograms protein x ml-1 had reduced the VMAX for [3H]glutamate uptake to approximately 20% of control, and the VMAX for [3H]GABA uptake to approximately 40% of control. This may enhance the factor's potential excitotoxicity.

Expression of the CD15 epitope in the human magnocellular basal forebrain system

The distribution of the carbohydrate epitope 3-fucosyl-N-acetyl-lactosamine (CD15) has been immunocytochemically evaluated in coronal paraffin sections through the magnocellular basal forebrain system--the nucleus basalis of Meynert, the nucleus of the diagonal band of Broca and the medial septal nucleus--of 202 human brains. The brains derived from differently aged controls (n = 54) and from patients suffering from organic brain diseases (n = 129) or psychiatric disorders (n = 19). In 30 cases dementia was clinically diagnosed. CD15 first appeared around birth when it became localized on singular astrocytes. The astrocyte number and process density steadily increased, and at approximately 12 years the typical adult-type pattern was acquired. Considerable variations in the expression patterns were noted with regard to the astrocyte number, the intensity in immunostaining and the process relations of CD15-positive astrocytes with the magnocellular neurons. In the light of these variations, and of conflicting additional changes in other areas of most diseased brains, it was difficult to correlate different intensities and patterns to specific diseases. The results, however, provide evidence for an increase in CD15 expression and in process network density of astrocytes in the lateral part of the nucleus basalis of Meynert in cases of Huntington's disease.

Two-site enzyme immunoassay for beta NGF applied to human patient sera

Nerve growth factor (NGF) supports sympathetic and sensory neurons in the peripheral nervous system and serves functions in the development and maintenance of cholinergic neurons in the basal forebrain. NGF distribution can be studied with the use of a sensitive two-site enzyme immunoassay (EIA). The monoclonal antibody 27/21 to mouse NGF was recently shown to effectively block the activity of both recombinant human NGF and native mouse NGF, and a two-site EIA using monoclonal antibody 27/21 was optimized. We have now applied this assay to examine NGF levels in normal human serum and serum from Parkinson, Alzheimer, and Huntington patients. To further test the specificity of conjugate binding, dilutions of the human sera were preincubated with an excess of monoclonal NGF antibody 27/21 in solution. With this strategy it was possible to completely block the signal obtained using the two-site EIA. Furthermore, we show that recombinant BDNF and NT-3 do not cross-react with monoclonal antibody 27/21 under our conditions. We found low levels of specific NGF immunoreactivity in normal human sera (0.4 +/- 0.1 ng/ml). Significantly lower levels of NGF were found in sera from patients with Parkinson's and Huntington's disease whereas sera from Alzheimer patients showed only slight reductions in the NGF level. Two patients who had received intracerebral NGF infusions (one with Parkinson's and other with Alzheimer's disease) showed significantly elevated serum levels of NGF during the period of infusion. Due to an inhibitory activity in human serum, it was impossible to demonstrate the low levels of NGF activity in the human serum samples using explanted embryonic sympathetic ganglia, even after concentration by pressure dialysis. Thus, the serum levels are below the limit to evoke a response in NGF-sensitive neurons and thus to expect any physiological effect. Nevertheless, the levels measured may be used as indicators in clinical conditions such as Parkinson's and Huntington's disease.

Oligoclonal free kappa and lambda bands in the cerebrospinal fluid of patients with multiple sclerosis and other neurological diseases. An immunoaffinity-mediated capillary blot study

We describe an affinity-mediated capillary blotting technique for the detection of free kappa or lambda light chains in native cerebrospinal fluid (CSF) after isoelectric focusing in agarose gel. Interferences by light chains bound to immunoglobulins were carefully excluded. An absolute amount of 20-50 ng of free kappa or lambda Bence-Jones proteins were detectable by this method, under the form of several discrete bands with isoelectric points between 5 and 8.5. No free light chains were observed in CSF and sera from patients without neurological disorders (n = 26). Such bands were present in most CSF samples in the case of central nervous system (CNS) infections, except in aseptic meningitis. In a group of 48 multiple sclerosis (MS) patients, 44 (92%) displayed oligoclonal free kappa bands restricted to the CSF; oligoclonal IgG bands were observed in 40 cases, and oligoclonal free lambda bands in 33. In this group, the presence of CSF free light chain bands was highly correlated with their absolute levels (p less than 0.001). In other neurological diseases (n = 44), oligoclonal free kappa and free lambda bands were detected much more rarely, in seven (16%) and four (9%) cases respectively. Surprisingly, the CSF from three unrelated patients with Huntington's disease (out of five tested) contained both oligoclonal IgG and free kappa bands.

Immunological status in Huntington's disease

The immunological status of patients with Huntington's disease was studied and compared with that of an age-matched control group. No remarkable abnormalities in lymphocyte subpopulations were observed. The percentage of B cells, CD4+, CD8+, DR+ cells and stimulated cells bearing Tac receptors remained unchanged. The proliferative response to mitogens and the production of interleukin-1 (Il-1) were decreased, whereas the IgG level was increased. It is possible that changes in the levels of neurotransmitters affect the immunological function in basal ganglia disease.

Neural grafting in a rat model of Huntington's disease: striosomal-like organization of striatal grafts as revealed by acetylcholinesterase histochemistry, immunocytochemistry and receptor autoradiography

Grafts of fetal striatum were implanted in the form of a cell suspension into the brains of rats with prior ibotenic acid lesions of the caudate-putamen. The grafts were placed in three different sites: the lesioned caudate-putamen, or the denervated (but otherwise undamaged) globus pallidus and substantia nigra. After 3-6 months survival the grafts were investigated by means of immunohistochemistry and receptor autoradiography in combination with routine histology and acetylcholinesterase histochemistry. The grafts placed within the lesioned caudate-putamen were at least 10-fold larger larger than those placed in the substantia nigra region, with the grafts placed in the globus pallidus being of intermediate size. In all locations the acetylcholinesterase staining had an uneven, patchy distribution, which was most pronounced in the grafts located within the caudate-putamen. These patches did not bear any obvious relationship to variations in density of the neuronal perikarya within the grafted tissue. Many of the neuropeptide-immunoreactive neuron types present in the normal striatum, such as those containing substance P, [Met]enkephalin, somatostatin, cholecystokinin and neuropeptide Y were also detected in the grafted striatum along with acetylcholinesterase-positive staining. Acetylcholinesterase-positive, [Met]enkephalin-positive, substance P-positive and tyrosine hydroxylase-positive markers all showed uneven, patchy distributions in the grafts. This was also the case for the distribution of dopamine D2 and opiate receptors (as revealed by [3H]spiroperidol and [3H]diprenorphine autoradiography, respectively), whereas muscarinic receptor binding was even throughout the grafts. As is the case in the so-called striosomal patches (neurochemically defined compartments) in the immature intact striatum during the early postnatal period, patches of high acetylcholinesterase staining in the grafts showed partial correspondence with patches of high [Met]enkephalin fibre staining, and dopamine receptor density, and (although to a lesser degree) also with patches of high opiate receptor density and high substance P-immunoreactivity. This correspondence of patches also occurred between tyrosine hydroxylase fibre staining and acetylcholinesterase staining as revealed by grafts placed into the substantia nigra. These results suggest that the fetal striatal cell suspension grafts will give rise to a fairly normal range of striatal neuron and receptor types and that they develop at least some of the striosomal features characteristic for the normal striatum.(ABSTRACT TRUNCATED AT 400 WORDS)

Elevated levels of a glycoprotein antigen (P-80) in gray and white matter of brain from victims of multiple sclerosis

The levels of a glycoprotein reactive with monoclonal antibody (MAb) 44D10 in white and gray matter from brains of victims of several neurological diseases, including Multiple Sclerosis, Alzheimer's, Parkinson's and Huntington's diseases, were compared to that of normal individuals. The concentration of antigen reactive with MAb 44D10 was elevated in both gray and white matter of all MS brains examined, but not in brains with other neurological diseases. The increase in the concentration of antigen varied amongst the MS brains, such that the levels of antigen were only slightly increased in 2 of the 6 MS brains whereas 2 to 4 fold higher levels were found in the other 4 brains. Increased levels of antigen were detected in gray matter of MS brains, whereas this antigen was either not detected or present in very low levels in gray matter homogenates prepared from age-matched normal brains. MAb Leu 1, which reacts with T lymphocytes, was not absorbed by normal and MS brain tissue suggesting the increase in antigen reactive with MAb 44D10 in MS brain homogenates was not associated with non-specific infiltration by T lymphocytes. Comparison of the purified antigen from MS gray matter and normal white matter by gel electrophoresis demonstrated that MAb 44D10 was reacting with a similar protein in both tissues with an apparent molecular weight of 80K. We have named this molecule P-80 glycoprotein.

Material prepared from normal brain inhibits migration of leukocytes from Huntington's disease patients

Material inhibiting migration of leukocytes in vitro from Huntington's disease patients, was obtained from human brain removed at autopsy. The active material was present in brainstem, basal ganglia and cerebellum but not in cerebral cortex. It could be recovered at autopsy up to 21.5 h after death, but not from patients who had died following prolonged anoxia. It was susceptible to heating and to freezing and thawing. Its activity was preserved in acid medium to pH 3, and its iso-electric point was around pH 5. Activity was present in the fraction eluted from gel filtration with molecular weight of 1.9 X 10(5). Protein, carbohydrate, lipid and nucleic acid could be identified in the active material, and its activity depended on intact protein and carbohydrate moieties. Sialic acid, although present, did not contribute to antigenicity. Extraction with lipid solvents abolished activity.

Evidence of T-lymphocyte functional impairment in Huntington's disease

Huntington's Disease (HD) is a degenerative neurological disorder with autosomal dominant transmission. Although immunological defect(s) have been postulated, no confirmed laboratory evidence for this exists. In the present study we observed activated T cells in the peripheral blood of HD patients (using 4F2 monoclonal antibody), whereas the percentage of T cells bearing T-cell activation markers such as HLA-DR and MLR4 antigens was normal. We then studied T cells of HD patients in some functional assays. Since it has been suggested that autologous mixed lymphocyte reaction (AMLR) includes several immune mechanisms in which distinct cell subsets interact and perform distinct regulatory functions, it is conceivable that the remarkable deficiency of AMLR herein observed in HD patients results from some abnormal immune regulation which may contribute to the pathology of this condition. Additional experiments demonstrated a defect of AMLR in three asymptomatic young sibs of HD patients, and coculture experiments between T cells of patients (as responders) and non-T cells of their sibs (as stimulators), and vice versa, produced no proliferative response. Subnormal responsiveness in allogeneic MLR was also observed. Normal or enhanced PHA-induced production of both IL-2 and IFN-gamma in vitro was detected. These experimental data suggest a cellular branch of the immune system in HD; however, they do not indicate if this defect is primary or secondary to the disease itself.