- Email: [email protected]
COTTON-WOOL SPOTS
1311
might be directed against the AChR component (or an intimately associated molecule) of an abnormal thymic epithelial cell, which has become abnormal ("foreign") for unknown reasons (? viral infestation); (2) co-reactivity of that antibody with AChR (or an associated molecule) at the neuromuscular junction would cause the weakness characteristic of myasthenia gravis (a "Sparafucile phenomenon"’); (3) mild epithelial-cell hyperplasia might be one response to an exogenous agent, while greater growth could result in thymoma, both associated with various degrees of local lymphocyte response and production of an IgG anti-AChR antibody, which can result in clinical myasthenia. (Because thymic epithelial cells are thought by some to be pluripotential, they could, through different antigenic components but by the same mechanisms, be instrumental in other dysimmune diseases sometimes associated with myasthenia gravis and/or thymic hyperplasia or thy-
from
being flooded with oxygen. Under conditions of hyperbaric
oxygenation the vascular bed of the canine retina overreacts to such a degree that microscopic foci of ischaemic necrosis develop. That this lesion is of ischaemic rather than histotoxic pathogenesis can be demonstrated by the addition of carbon dioxide to the respiratory gas. This procedure protects the retina from the oxygen-induced cytoid-body change. As the result of the vasodilating action of the carbon dioxide, however, the direct toxic action of oxygen
on
the brain is aug-
mented, and convulsive responses, paralysis, neuronal necrosis and death are accelerated in onset and increased in incidence. These results, incidentally, create an interesting therapeutic paradox in this experimental model. Department of Pathology, Dartmouth Medical School, Hanover, New Hampshire 03755,
U.S.A.
GEORGE MARGOLIS
moma.) An abnormal antimuscle IgG antibody always co-reacting with thymic "epithelial cells" was previously found in a third of myasthenia-gravis patients, nearly all those with thymomas, and a quarter of thymoma patients without myasthenia gravis.8.9 The cross-reacting thymic cells were later considered "myoid" .10 However, electron-microscopy of three thymuses from our series showed the hyperplastic epithelial cells to have ultrastructural characteristics of epithelial cells (desmosomes, tonofobrils) and no features of striated muscle fibres." Normal-appearing striated-muscle fibres can grow out of normal animal’z,’3 thymus in tissue culture, but we do not know whether the cell of origin is extrathymic or intrathymic or which cell type if intrathymic; electronmicroscopy of our cultured myasthenia thymuses has failed to demonstrate them. 14 It is moot whether thymic cells with epithelial-like ultrastructure and muscle-like AChR should be called epithelial or myoid, or both. But either way their possible role in the pathogenesis of myasthenia gravis can be further suspected from our
study. Guy Cunningham, Katherine Oliver, Elizabeth S. Mingioli, Priscilla Chauvin, and Rick Zirzow provided technical assistance. Medical Neurology and Neuroimmunology Branches National Institute of Neurological and Communicative Disorders and Stroke, W. KING ENGEL and Surgery Branch, National Heart, Lung JOHN L. TROTTER and Blood Institute, DALE E. MCFARLIN National Institutes of Health, CHARLES L. MCINTOSH Bethesda, Maryland 20014, U.S.A.
COTTON-WOOL SPOTS
SIR,-To your discussion of the pathogenesis of cotton-wool (May 7, p.989) one piece of experimental evidence sup-
spots
porting the ischasmic-infarct hypothesis may be added. By exposing dogs to 100% oxygen at 3 atmospheres absolute pressure for 4-6 h
a characteristic retinal lesion, manifested as the cytoid-body change-the microscopic counterpart of the cotton-wool spot-is induced.’·2 The pathogenesis of this lesion is explained as follows. Oxygen at high concentrations is a potent cell toxin to which the vascular system responds by a generalised vasoconstrictor action, a reaction interpreted as a homoeostatic protective mechanism preventing the tissues
7. Engel, W. K. ibid. 1976, 274, 623. 8. Van der Geld, H. W. R., Feltkamp, T. E. W., Oosterhuis, D. G. H. Proc. Soc. exp. Biol. Med. 1964, 115, 782. 9. Strauss, A. J. L., Smith, C. W., Cage, G. W., Van der Geld, H. W. R., McFarlin, D. E., Barlow, M. Ann.N.Y. Acad. Sci. 1966, 135, 557. 10. Van de Velde, R. L., Friedman, N. B. Am.J. Path. 1970, 59, 347. 11. Shebert, R. T., Engel, W. K. Unpublished. 12. Wekerle, H., Paterson, B., Ketelsen, U.-P., Feldman, M. Nature, 1975, 256, 493. 13. Kuo, I., Drachman, D. B.Neurology, 1976, 26, 383. 14. Askanas, V., Engel, W. K. Unpublished. 1. Margolis, G., Brown, I. W., Jr. Science, 1966, 151, 466. 2. Margolis, G., Brown, I. W., Jr., Fuson, R. W., Moor, G. F. 3rd Int. Congr. Hyperbaric Med. 1965, p. 133.
&bgr;-THROMBOGLOBULIN TEST SIR,-Iwould like to comment on two aspects of Dr O’Brien and his colleagues’ results (May 28, p. 1153) since they have failed to confirm studies by me and my colleagues on the value of measuring the plasma concentration of the platelet-specific protein p-thromboglobulin in the diagnosis of’ihromboembolism.1.2 Firstly, p-thromboglobulin levels were compared with the heparin-neutralising capacity of plasma as measured by the heparin thrombin clotting-time (H.T.C.T.). This may measure platelet factor 4 (P.F.4), another protein unique to platelets. It is essential to stress the very important differences in the methods for preparing the plasma for these two assays. During centrifugation at room temperature to prepare platelet-poor plasma (for the H.T.c.T.) O’Brien’ found that platelets undergo the release reaction. Thus the levels of plasma P.F.4 under these conditions reflect the ability of platelets to release this protein in vitro. In an attempt to overcome this problem Cash and I developed a method to inhibit the release reaction by collecting blood into antiplatelet reagents and by cooling it before centrifugation.’’ This resulted in a thirty-fold reduction in the plasma concentration of p-thromboglobulin, and the level as measured in vitro may reflect the true circulating concentration in vivo. This is one important reason why there is no correlation between p-thromboglobulin and the H.T.C.T. If, however, P.F.4 is measured in plasma samples (prepared at 0°C with antiplatelet reagents) by a radioimmunoassay a significant correlation is found (r=0- 77). Secondly, I should like to draw attention to important differences between the patients we studied and those reported on by Dr O’Brien and his colleagues. He reported results on "12 patients in hospital 7-240 days after gross D.v.T. Some were on anticoagulants ...". No details of diagnostic criteria for deep-vein thrombosis are given; clinical diagnosis alone, without use of a diagnostic procedure such as venography, is unreliable. In our study’ all patients had venograms, and bloodsamples were collected at the time of initial investigations before treatment. Raised plasma-j3-thromboglobulin concentration in patients with deep-vein thrombosis fall during treatment with anticoagulants, and it is therefore not surprising that many of Dr O’Brien’s patients had a normal plasma-(3-
thromboglobulin. Dr O’Brien and his colleagues also studied patients with myocardial infarction and found that all but 2 of 17 patients
had normal plasma-p-thromboglobulin concentration. In view of the interesting letter by Dr Denham and his colleagues (May 28, p. 1154) reporting raised 3-thrornboglobulin levels in myocardial-infarction patients with thromboembolism it would have been useful to know more about Dr O’Brien’s two pa1. 2.
Ludlam, C. A., Bolton, A. E., Moore, S., Cash, J. D. Lancet, 1975, ii, 259. Pepper, D. S., Ludlam, C. A. in Platelets and Thrombosis (edited by F. I.
3. 4.
Pareti and D. C. B. Mills). London (in the press). O’Brien, J. R., Lancet, 1968, , 779. Ludlam, C. A., Cash, J. D. Br. J. Hœmat. 1976, 33, 239.
might be directed against the AChR component (or an intimately associated molecule) of an abnormal thymic epithelial cell, which has become abnormal ("foreign") for unknown reasons (? viral infestation); (2) co-reactivity of that antibody with AChR (or an associated molecule) at the neuromuscular junction would cause the weakness characteristic of myasthenia gravis (a "Sparafucile phenomenon"’); (3) mild epithelial-cell hyperplasia might be one response to an exogenous agent, while greater growth could result in thymoma, both associated with various degrees of local lymphocyte response and production of an IgG anti-AChR antibody, which can result in clinical myasthenia. (Because thymic epithelial cells are thought by some to be pluripotential, they could, through different antigenic components but by the same mechanisms, be instrumental in other dysimmune diseases sometimes associated with myasthenia gravis and/or thymic hyperplasia or thy-
from
being flooded with oxygen. Under conditions of hyperbaric
oxygenation the vascular bed of the canine retina overreacts to such a degree that microscopic foci of ischaemic necrosis develop. That this lesion is of ischaemic rather than histotoxic pathogenesis can be demonstrated by the addition of carbon dioxide to the respiratory gas. This procedure protects the retina from the oxygen-induced cytoid-body change. As the result of the vasodilating action of the carbon dioxide, however, the direct toxic action of oxygen
on
the brain is aug-
mented, and convulsive responses, paralysis, neuronal necrosis and death are accelerated in onset and increased in incidence. These results, incidentally, create an interesting therapeutic paradox in this experimental model. Department of Pathology, Dartmouth Medical School, Hanover, New Hampshire 03755,
U.S.A.
GEORGE MARGOLIS
moma.) An abnormal antimuscle IgG antibody always co-reacting with thymic "epithelial cells" was previously found in a third of myasthenia-gravis patients, nearly all those with thymomas, and a quarter of thymoma patients without myasthenia gravis.8.9 The cross-reacting thymic cells were later considered "myoid" .10 However, electron-microscopy of three thymuses from our series showed the hyperplastic epithelial cells to have ultrastructural characteristics of epithelial cells (desmosomes, tonofobrils) and no features of striated muscle fibres." Normal-appearing striated-muscle fibres can grow out of normal animal’z,’3 thymus in tissue culture, but we do not know whether the cell of origin is extrathymic or intrathymic or which cell type if intrathymic; electronmicroscopy of our cultured myasthenia thymuses has failed to demonstrate them. 14 It is moot whether thymic cells with epithelial-like ultrastructure and muscle-like AChR should be called epithelial or myoid, or both. But either way their possible role in the pathogenesis of myasthenia gravis can be further suspected from our
study. Guy Cunningham, Katherine Oliver, Elizabeth S. Mingioli, Priscilla Chauvin, and Rick Zirzow provided technical assistance. Medical Neurology and Neuroimmunology Branches National Institute of Neurological and Communicative Disorders and Stroke, W. KING ENGEL and Surgery Branch, National Heart, Lung JOHN L. TROTTER and Blood Institute, DALE E. MCFARLIN National Institutes of Health, CHARLES L. MCINTOSH Bethesda, Maryland 20014, U.S.A.
COTTON-WOOL SPOTS
SIR,-To your discussion of the pathogenesis of cotton-wool (May 7, p.989) one piece of experimental evidence sup-
spots
porting the ischasmic-infarct hypothesis may be added. By exposing dogs to 100% oxygen at 3 atmospheres absolute pressure for 4-6 h
a characteristic retinal lesion, manifested as the cytoid-body change-the microscopic counterpart of the cotton-wool spot-is induced.’·2 The pathogenesis of this lesion is explained as follows. Oxygen at high concentrations is a potent cell toxin to which the vascular system responds by a generalised vasoconstrictor action, a reaction interpreted as a homoeostatic protective mechanism preventing the tissues
7. Engel, W. K. ibid. 1976, 274, 623. 8. Van der Geld, H. W. R., Feltkamp, T. E. W., Oosterhuis, D. G. H. Proc. Soc. exp. Biol. Med. 1964, 115, 782. 9. Strauss, A. J. L., Smith, C. W., Cage, G. W., Van der Geld, H. W. R., McFarlin, D. E., Barlow, M. Ann.N.Y. Acad. Sci. 1966, 135, 557. 10. Van de Velde, R. L., Friedman, N. B. Am.J. Path. 1970, 59, 347. 11. Shebert, R. T., Engel, W. K. Unpublished. 12. Wekerle, H., Paterson, B., Ketelsen, U.-P., Feldman, M. Nature, 1975, 256, 493. 13. Kuo, I., Drachman, D. B.Neurology, 1976, 26, 383. 14. Askanas, V., Engel, W. K. Unpublished. 1. Margolis, G., Brown, I. W., Jr. Science, 1966, 151, 466. 2. Margolis, G., Brown, I. W., Jr., Fuson, R. W., Moor, G. F. 3rd Int. Congr. Hyperbaric Med. 1965, p. 133.
&bgr;-THROMBOGLOBULIN TEST SIR,-Iwould like to comment on two aspects of Dr O’Brien and his colleagues’ results (May 28, p. 1153) since they have failed to confirm studies by me and my colleagues on the value of measuring the plasma concentration of the platelet-specific protein p-thromboglobulin in the diagnosis of’ihromboembolism.1.2 Firstly, p-thromboglobulin levels were compared with the heparin-neutralising capacity of plasma as measured by the heparin thrombin clotting-time (H.T.C.T.). This may measure platelet factor 4 (P.F.4), another protein unique to platelets. It is essential to stress the very important differences in the methods for preparing the plasma for these two assays. During centrifugation at room temperature to prepare platelet-poor plasma (for the H.T.c.T.) O’Brien’ found that platelets undergo the release reaction. Thus the levels of plasma P.F.4 under these conditions reflect the ability of platelets to release this protein in vitro. In an attempt to overcome this problem Cash and I developed a method to inhibit the release reaction by collecting blood into antiplatelet reagents and by cooling it before centrifugation.’’ This resulted in a thirty-fold reduction in the plasma concentration of p-thromboglobulin, and the level as measured in vitro may reflect the true circulating concentration in vivo. This is one important reason why there is no correlation between p-thromboglobulin and the H.T.C.T. If, however, P.F.4 is measured in plasma samples (prepared at 0°C with antiplatelet reagents) by a radioimmunoassay a significant correlation is found (r=0- 77). Secondly, I should like to draw attention to important differences between the patients we studied and those reported on by Dr O’Brien and his colleagues. He reported results on "12 patients in hospital 7-240 days after gross D.v.T. Some were on anticoagulants ...". No details of diagnostic criteria for deep-vein thrombosis are given; clinical diagnosis alone, without use of a diagnostic procedure such as venography, is unreliable. In our study’ all patients had venograms, and bloodsamples were collected at the time of initial investigations before treatment. Raised plasma-j3-thromboglobulin concentration in patients with deep-vein thrombosis fall during treatment with anticoagulants, and it is therefore not surprising that many of Dr O’Brien’s patients had a normal plasma-(3-
thromboglobulin. Dr O’Brien and his colleagues also studied patients with myocardial infarction and found that all but 2 of 17 patients
had normal plasma-p-thromboglobulin concentration. In view of the interesting letter by Dr Denham and his colleagues (May 28, p. 1154) reporting raised 3-thrornboglobulin levels in myocardial-infarction patients with thromboembolism it would have been useful to know more about Dr O’Brien’s two pa1. 2.
Ludlam, C. A., Bolton, A. E., Moore, S., Cash, J. D. Lancet, 1975, ii, 259. Pepper, D. S., Ludlam, C. A. in Platelets and Thrombosis (edited by F. I.
3. 4.
Pareti and D. C. B. Mills). London (in the press). O’Brien, J. R., Lancet, 1968, , 779. Ludlam, C. A., Cash, J. D. Br. J. Hœmat. 1976, 33, 239.