Timo Paavonen

Infiltrates of Activated Mast Cells at the Site of Coronary Atheromatous Erosion or Rupture in Myocardial Infarction

BACKGROUND Erosion and rupture of coronary atheromas are the events preceding the vast majority of acute coronary syndromes. The shoulder regions of atheromas, the sites at which erosion or rupture is most likely to occur, are the sites at which mast cells accumulate. These cells are filled with neutral proteases capable of triggering extracellular matrix degradation via activation of matrix metalloproteinases. To obtain more direct evidence for the participation of mast cells in the acute coronary syndromes, we quantified the numbers of mast cells at eroded or ruptured sites of coronary atheromas in patients who died of myocardial infarction. METHODS AND RESULTS In specimens of coronary arteries from 20 patients who had died of acute myocardial infarction, the site of atheromatous erosion or rupture was identified. The specimens were stained with monoclonal antibodies against the two major proteases of mast cells, tryptase and chymase, and against macrophages, T lymphocytes, and smooth muscle cells. At the immediate site of erosion or rupture, mast cells amounted to 6% of all nucleated cells, in the adjacent atheromatous area to 1%, and in the unaffected intimal area to 0.1%. The proportions of these mast cells that were activated, ie, had been stimulated to degranulate and release some of their tryptase and chymase contents, were 86% at the site of erosion or rupture, 63% in the adjacent atheromatous area, and 27% in the unaffected intima. At the site of erosion or rupture, the numbers of macrophages and T lymphocytes were also increased, but the number of smooth muscle cells was decreased. CONCLUSIONS The accumulation of activated mast cells (200-fold more than in the unaffected coronary intima) at the site of atheromatous erosion or rupture suggests that in thrombotic coronary occlusion the role played by mast cells is significant.

Arrhythmic disorder mapped to chromosome 1q42–q43 causes malignant polymorphic ventricular tachycardia in structurally normal hearts

OBJECTIVES The purpose of this study was to provide clinical and anatomical characteristics as well as genetic background of a malignant arrhythmogenic disorder. BACKGROUND An inherited autosomally dominant cardiac syndrome causing stress-induced polymorphic ventricular tachycardia and syncope in the absence of structural myocardial changes was detected in two families. METHODS Two unrelated families with six victims of sudden death and 51 living members were evaluated. Resting and exercise electrocardiograms (ECG), echocardiography, magnetic resonance imaging (MRI), cineangiography, microscopic examination of endomyocardial biopsies and a drug testing with a class IC antiarrhythmic agent flecainide were performed. A genetic linkage analysis was carried out to map the gene locus. RESULTS Of the 24 affected individuals, 10 had succumbed with six cases of sudden death, and 14 survivors showed evidence of disease. Exercise stress test induced ventricular bigeminy or polymorphic ventricular tachycardia in affected individuals. Three children initially examined before 10 years of age developed arrhythmias during a four-year follow-up. Resting ECGs were normal in affected subjects except a slight prolongation of the QT intervals adjusted for heart rate (QTc) (430 +/- 18 vs. 409 +/- 19 ms, affected vs. nonaffected, p < 0.01). Administration of flecainide did not induce ECG abnormalities encountered in familial idiopathic ventricular fibrillation. Ventricular volumes, contractility and wall measurements were normal by echocardiography, right ventricular cineangiography and MRI. Histopathological examination showed no fibrosis or fatty infiltration. The cumulative cardiac mortality by the age of 30 years was 31%. The disease locus was assigned to chromosome 1q42-q43, with a maximal pairwise lod score of 4.74 in the two families combined. Only one heterozygous carrier was clinically unaffected suggesting high disease penetrance in adulthood. CONCLUSIONS A distinct cardiac disorder linked to chromosome 1q42-q43 causes exercise-induced polymorphic ventricular tachycardia in structurally normal hearts and is highly malignant. Delayed clinical manifestation necessitates repeated exercise electrocardiography to assure diagnosis in young individuals of the families.

Association Between Myocardial Infarction and the Mast Cells in the Adventitia of the Infarct-Related Coronary Artery

BACKGROUND Histamine, a product of mast cells, is an effective vasoconstrictor of atherosclerotic coronary arteries. Because it has been suggested that coronary spasm plays a role in acute coronary syndromes such as myocardial infarction (MI), we quantified and characterized the mast cells in the adventitia of infarct-related coronary arteries. METHODS AND RESULTS In a series of 17 autopsied MI patients, we identified the segment of the left coronary artery with ruptured plaque responsible for the infarction. More distal segments from the infarct-related coronary artery, either with nonruptured plaques or with normal intima, were also studied. Corresponding segments taken from left coronary arteries obtained from 17 patients who had died of noncardiac causes served as controls. Adventitial mast cells in the infarct-related and the control coronary arteries were identified immunohistochemically by staining for tryptase. In the infarct-related coronary arteries, we also stained for chymase and histamine. Moreover, T lymphocytes and macrophages were identified immunohistochemically and counted. In the infarct-related coronary arteries, significantly larger numbers of mast cells were present in the adventitia backing ruptured plaques (98+/-40 mast cells/mm2, mean+/-SD) than in the adventitia backing nonruptured plaques (41+/-12 mast cells/mm2; P<0.001) or backing normal intima (19+/-8 mast cells/mm2; P<0.001). No such difference was found among the 3 different segments in the control coronary arteries. The majority of mast cells contained not only tryptase but also chymase. Mast cells were the only cells in the coronary adventitia that contained histamine. The proportion of adventitial mast cells that were degranulated was highest in the segments with ruptured plaques. The numbers of adventitial macrophages and T lymphocytes were also increased in the segments with plaque rupture. CONCLUSIONS In infarct-related coronary arteries, the number of degranulated mast cells in the adventitia backing ruptured plaques is increased. Histamine released from the degranulated mast cells may reach the media, where it may locally provoke coronary spasm and thus contribute to the onset of MI.

Chronic Allograft Rejection

The short-term results of organ transplantation have significantly improved during the past few years. However, long-term success has remained on the same level as in the pre-cyclosporine era, with the half-life of a renal transplant being 7 years or more (Cho & Terasaki 1988). Although chronic rejection may not be the sole reason for transplants being lost during subsequent years, there is good recent evidence indicating that it is a leading cause in late graft failure (Kirkman et al. 1982, Mahony & Sheil 1987, Dennis et al. 1989). There are several recent publications (Paul & Solez 1991, Paul & Fellstrom 1992, Foegh 1990, Tilney et al. 1991, Adams & Tilney 1989, Fellstrom et al. 1989a) that give good overviews on different clinical and biological parameters of chronic allograft rejection. In this communication we will primarily concentrate on our own experience.

Sirolimus‐Based Therapy Following Early Cyclosporine Withdrawal Provides Significantly Improved Renal Histology and Function at 3 Years

Graft function and histology are predictive of renal transplant survival. The Rapamune Maintenance Regimen study demonstrated that early cyclosporine (CsA) withdrawal from a sirolimus (SRL)‐CsA‐steroid (ST) regimen improved renal function and blood pressure. We report the protocol‐mandated biopsy findings from that study. Renal transplant patients (n = 430) receiving SRL‐CsA‐ST were randomized at 3 months after transplantation to remain on SRL‐CsA‐ST, or to have CsA withdrawn (SRL‐ST group). Protocol‐mandated biopsies were performed at engraftment and at 12 and 36 months. Two pathologists blindly evaluated 484 biopsies to obtain the Chronic Allograft Damage Index (CADI) scores. At 36 months among patients with serial biopsies (n = 63), the mean CADI score was significantly lower with SRL‐ST(4.70 vs. 3.20, p = 0.003), as was the mean tubular atrophy score (0.77 vs. 0.32, p < 0.001). All six components of the CADI score were numerically lower in SRL‐ST group; moreover, inflammation and the tubular atrophy scores decreased significantly in the SRL‐ST group between 12 and 36 months. The calculated glomerular filtration rate at 36 months was significantly better in the CsA‐withdrawal group (54.8 vs. 68.2 mL/min, p = 0.009). In conclusion, withdrawing CsA from the SRL‐CsA‐ST regimen resulted in improved renal histology and function.

Chronic rejection in rat aortic allografts. An experimental model for transplant arteriosclerosis.

Chronic rejection has several histological appearances, depending on the type of organ graft. Common to all of them is transplant arteriosclerosis associated with an ongoing inflammatory response in the transplanted graft. To the contrary of classical atherosclerosis, in which the manifestations are mostly focal, proximal, and asymmetric, transplant arteriosclerosis is generalized, and the intimal thickening is concentric. In this article, we describe an experimental animal model whereby transplant arteriosclerosis may be investigated in the inbred rat. Aortic allografts were transplanted from DA (RTIa) to major histocompatibility complex-incompatible WF (RTIv) rats or, for control, to rats of the DA strain. Transplantation was followed by an acute inflammation episode in the aortic adventitia of the allograft, largely lacking in the syngeneic graft, with a prominence of lymphoid activation markers (Cd25) in the cells of the inflammatory infiltrate. The inflammation episode peaked at 2 months after transplantation, became attenuated, and was followed by a proliferative response of myocytes in the allograft media. An increase in the migration of myocytes to the subendothelial space (presumably through small breaks generated in the internal elastic lamina) was observed thereafter, and myocyte proliferation continued in the intima with some intermingled macrophages. Finally, necrosis and disappearance of myocytes and their replacement by fibrous tissue were observed in the media. These alterations are virtually identical with the vascular lesion of chronically rejecting parenchymal organ transplants in human subjects. We suggest that aortic allografts exchanged between histoincompatible rat strains may be used as an experimental model for transplant arteriosclerosis.

Binding of progestins to the glucocorticoid receptor: Correlation to their glucocorticoid-like effects on in vitro functions of human mononuclear leukocytes

A number of physiological and synthetic progestins were tested for their ability to compete with [3H]dexamethasone for the binding to the glucocorticoid receptor of human mononuclear leukocytes and their ability to elicit glucocorticoid-like effects on the same cells. As compared to the reference compound dexamethasone (relative receptor binding affinity defined as 100%), two potent synthetic progestins with a pregnane-type structure, megestrol acetate and medroxyprogesterone acetate, were found to display a considerable binding affinity towards the receptor (46 and 42%, respectively). The relative binding affinity of the naturally occurring ligand, cortisol, to the receptor was clearly lower (25%). The effective binding of medroxyprogesterone acetate to the glucocorticoid receptor was confirmed by direct binding studies utilizing a tritiated derivative of this steroid. No evidence for the existence of a specific progesterone receptor in human mononuclear leukocytes was obtained as judged by the results of competition experiments where a progesterone receptor-specific ligand [3H]Org 2058 was used. Medroxyprogesterone acetate and megestrol acetate also induced glucocorticoid-like effects on the lymphocyte functions. These included inhibition of the proliferative responses to the T-cell mitogens concanavalin A and phytohaemagglutinin and an enhanced accumulation of immunoglobulin secreting cells in pokeweed mitogen-stimulated cultures. The progestin effect appears to be mediated through a radiosensitive (suppressor) subpopulation of T lymphocytes. In contrast, the synthetic progestins related structurally to 19-nortestosterone, norethisterone and d-norgestrel, were virtually devoid of binding affinity towards the glucocorticoid receptor nor did they measurably influence the in vitro lymphocyte functions. These studies demonstrate that certain progestins in common clinical use probably possess inherent glucocorticoid activity and suggest that side effects attributable to this character (e.g. suppression of the pituitary-adrenal axis) might be expected when these compounds are used in pharmacological doses.

International variation in histologic grading is large, and persistent feedback does not improve reproducibility.

Histologic grading systems are used to guide diagnosis, therapy, and audit on an international basis. The reproducibility of grading systems is usually tested within small groups of pathologists who have previously worked or trained together. This may underestimate the international variation of scoring systems. We therefore evaluated the reproducibility of an established system, the Banff classification of renal allograft pathology, throughout Europe. We also sought to improve reproducibility by providing individual feedback after each of 14 small groups of cases. Kappa values for all features studied were lower than any previously published, confirming that international variation is greater than interobserver variation as previously assessed. A prolonged attempt to improve reproducibility, using numeric or graphical feedback, failed to produce any detectable improvement. We then asked participants to grade selected photographs, to eliminate variation induced by pathologists viewing different areas of the slide. This produced improved kappa values only for some features. Improvement was influenced by the nature of the grade definitions. Definitions based on “area affected” by a process were not improved. The results indicate the danger of basing decisions on grading systems that may be applied very differently in different institutions.

Protocol Core Needle Biopsy and Histologic Chronic Allograft Damage Index (CADI) as Surrogate End Point for Long-Term Graft Survival in Multicenter Studies

This study is an investigation of whether a protocol biopsy may be used as surrogate to late graft survival in multicenter renal transplantation trials. During two mycophenolate mofetil trials, 621 representative protocol biopsies were obtained at baseline, 1 yr, and 3 yr. The samples were coded and evaluated blindly by two pathologists, and Chronic Allograft Damage Index (CADI) score was constructed. At 1 yr, only 20% of patients had elevated (>l.5 mg/100 ml) serum creatinine, whereas 60% of the biopsies demonstrated an elevated (>2.0) CADI score. The mean CADI score at baseline, 1.3 +/- 1.1, increased to 3.3 +/- 1.8 at 1 yr and to 4.1 +/- 2.2 at 3 yr. The patients at 1 yr were divided into three groups, those with CADI <2, between 2 and 3.9, and >4.0, the first two groups having normal (1.4 +/- 0.3 and 1.5 +/- 0.6 mg/dl) and the third group pathologic (1.9 +/- 0.8 mg/dl) serum creatinine. At 3 yr, there were no lost grafts in the low CADI group, six lost grafts (4.6%) in the in the elevated CADI group, and 17 lost grafts (16.7%) in the high CADI group (P < 0.001). One-year histologic CADI score predicts graft survival even when the graft function is still normal. This observation makes it possible to use CADI as a surrogate end point in prevention trials and to identify the patients at risk for intervention trials.

Hormonal Regulation of Immune Responses

Females have stronger immune responses than males. Female predominance in autoimmune diseases in both experimental animals and in man is also established. Sex hormones and some other steroid hormones have been shown to exert immunoregulatory effects in both in vivo and in vitro situations. Important mechanisms of hormone action on lymphocytes have gradually been revealed. In this paper the most intriguing effects of steroid hormones on immune system and present data suggesting hormonal influence on the pathogenesis of autoimmune diseases are summarized.