TOTAL SERUM IMMUNOGLOBULINS IN TRANSPLANT CARDIAC RECIPIENTS: CORRELATION OF IgA LEVELS WITH CORONARY ATHEROSCLEROSIS IN THE NATIVE HEART
Andriy Morgun, MD,a Natalia Shulzhenko, MD,a Aparecida P. Nagao, PhD,b Marcello Franco, MD, PhD,c Márcia M. Souza, MD, PhD,c Dirceu R. Almeida, MD, PhD,d Rosiane V.Z. Diniz, MD,d Antonio C.C. Carvalho, MD, PhD,d Maria Gerbase-DeLima, MD, PhDa
From the Division of Allergy, Clinical Immunology and Rheumatology, Department of Pediatrics,a Department of Pathology, c and Division of Cardiology, Department of Medicine, d Universidade Federal de São Paulo - Escola Paulista de Medicina (UNIFESP-EPM); and from the Department of Immunology, Instituto de Ciências Biomédicas, Universidade de São Paulo. b
Corresponding author: Maria Gerbase-DeLima,
MD, Rua dos Otonis, 725, 04025-002 São Paulo, SP, Brazil; business telephone number: 55
11 5764426;
home telephone number: 55 11 2404949; fax number: 55 11 5701590;
e-mail:ger.dped@epm.br
This investigation was partially supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).
Abstract; Introduction; Material and Methods; Results; Discussion; References
Background: The purpose of the present study was to investigate whether pre-transplant serum IgA levels are a prognostic indicator of cardiac allograft outcome, as reported for kidney allografts in which high pre-transplant serum IgA concentrations are associated with a good prognosis. Methods: We determined serum IgA, IgM and IgG levels in pre-transplant sera from 41 cardiac graft recipients and, in addition, in 1 year post-transplant sera from 28 of these recipients. Results: No difference was detected in IgA levels between recipients that survived or not the first year post-transplant, or between those that presented or not at least one grade 3A rejection episode during the first 6 months after transplantation. On the other hand, we observed that the levels of IgA, IgM and IgG in pre-transplant sera were approximately twice as high as those of healthy individuals. These levels remained unchanged in the post-transplant period, except for a decrease of IgA concentration in patients that presented coronary atherosclerosis in the native heart. Conclusion: It is possible that the increased serum levels of IgA in candidates for heart transplantation, secondary to coronary atherosclerosis and to other unidentified conditions, could represent a confounding factor for the investigation of the relationship between pre-transplant serum IgA levels and cardiac graft outcome.
Identification of factors that influence cardiac transplantation outcome could potentially allow rejection surveillance protocols and anti-rejection pharmacological regimens to be more cost-effective for low-risk patients and intensified for high-risk patients. Although previous studies have identified subsets of patients which are at differing risk for early or cumulative rejection,1,2 considerable variation exists within these subsets. Considering that in kidney transplantation it has been shown that patients with pre-transplant serum immunoglobulin A (IgA) concentration higher than the mean value observed for all the recipients (around 200 mg/dl ) exhibited a better one-year graft survival than those with lower serum IgA,3,4 the purpose of the present study was to investigate whether the same phenomenon could be demonstrated in cardiac transplantation. In addition, we have measured post-transplant IgA, as well as pre- and post-transplant serum IgM and IgG levels.
Patient population
The study was conducted on 41 adult cardiac allograft recipients. Thirty-one were male. The basic diseases were: dilated cardiomyopathy (10 cases), ischemic myocardiopathy (14 cases), and Chagas’ myocardiopathy (17 cases). The presence of concomitant coronary atherosclerosis (CA) was evaluated by means of the histological examination of the recipients’ native hearts.
All patients were maintained on standard triple therapy immunosuppression consisting of cyclosporine (4-6 mg/kg/day), azathioprine (2 mg/kg/day), and prednisone (0.2 mg/kg/day). Treatment for rejection consisted of pulse therapy with methylprednisolone (1 g daily for 3 days) and/or augmentation of the oral doses of prednisone and cyclosporine.
Endomyocardial biopsies were routinely collected weekly for the first 4 weeks, every 15 days during the second month, and once a month from the third to the sixth month. Additional biopsies were performed because of a clinical hypothesis of rejection or for the follow-up of a rejection episode. The results of histologic examination were graded according to the International Society for Heart and Lung Transplantation (ISHLT) criteria.5
Ethical committee approval and informed consent were obtained.
Serum immunoglobulin measurements
Serum concentrations of IgA, IgM and IgG were determined by radial immunodifusion assay. The calibration curves were constructed with reference solutions of IgA (265 mg/dl), IgM (177 mg/dl) and IgG (324 mg/dl) purchased from Behring, São Paulo, Brazil.
Statistical analysis
Statistical comparisons were performed by the Mann-Whitney test for unpaired samples, and by the Wilcoxon test for paired samples.
Relationship between pre-transplant serum IgA levels and graft evolution
Pre-transplant serum IgA levels did not differ between patients that survived (n=34) or not (n=7) the first post-transplant year (Figure 1a) or between patients that presented (n=34) or not (n=7) at least one grade 3A rejection episode during the first 6 months after transplantation (Figure 1b).
Comparison of IgA, IgM and IgG levels between pre-transplant sera and sera from healthy individuals.
The levels of Igs observed in pre-transplant sera from 41 patients were significantly (p<0.001 in all comparisons) higher than in sera from 30 healthy adult controls, being the median values: IgA, 432 vs. 179 mg/dl; IgM, 252 vs. 123 mg/dl; and IgG, 1880 vs. 986 mg/dl, respectively.
Comparison of IgA, IgM and IgG levels between pre- and post-transplant sera
This analysis comprised data from 28 recipients of whom both pre- and 1 year post-transplant serum samples were available. As shown in TABLE 1, the serum IgA levels presented a decline in the post-transplant period, with median values of 432 and 276 mg/dl in pre- and post-transplant sera, respectively (p=0.0002). In contrast, no difference was observed in respect to IgM or IgG levels.
Relationship between serum IgA levels and coronary atherosclerosis
Among the 28 recipients for whom both pre- and post-transplant serum samples were available, 18 presented histological evidence of coronary atherosclerosis (CA) in the native heart. Comparison of the pre-transplant serum IgA levels between patients with and without CA (Fig. 2) showed higher values in the former group (median values: 464 versus 372 mg/dl, p< 0.05). The serum IgA levels in patients without CA were, nonetheless, higher than those of healthy controls (372 versus 179 mg/dl, p < 0.001).
A decline in serum IgA levels after transplant was observed in patients with CA (median values: 464 versus 276 mg/dl in pre- and post-transplant samples, respectively; p < 0.0001), whereas no difference between pre- and post-transplant levels was observed in the group of patients without CA (Figure 2). Considering post-transplant sera, no difference in serum IgA levels was detected between patients with and without CA (median values: 276 versus 272 mg/dl) (Figure 2).
The relationship between pre-transplant serum IgA levels and the cardiac allograft outcome was investigated by comparing IgA concentrations between patients that survived or not the first post-transplant year, and also between patients that presented or not at least one grade 3A rejection episode during the first 6 months post-transplantation. No difference was detected in either of these comparisons. Therefore, the phenomenon of an improved graft outcome in recipients with increased pre-transplant serum IgA reported in kidney transplantation3,4 does not seem to be present in heart transplantation.
It should be mentioned, however, that in kidney transplantation the impact of serum IgA concentrations on graft survival was assessed in much larger samples of patients. Furthermore, it has also been demonstrated that, in addition to high total serum IgA levels, further improvement of the kidney graft outcome was associated with the presence of IgA autoantibodies directed against the Fab fragment or the hinge region of human IgG.3,4,7 It would, therefore, be interesting to test the pre-transplant sera of cardiac allograft recipients for the presence of these autoantibodies.
In contrast to patients awaiting kidney transplants, which present serum IgA levels within the normal range,3,4,6,7 cardiac transplant candidates have increased serum IgA levels as compared to healthy controls. This characteristic could represent a confounding factor for the investigation of the association between IgA levels and transplant outcome.
The high levels of IgA in the pre-transplant sera of cardiac transplant recipients was an unexpected finding of our study. Our data suggest that at least part of this increase could be attributed to the previously reported association of high IgA levels with atherosclerosis,8 since IgA levels were higher in patients with than in those without histologically proven CA in the native heart. Muscari and colleagues8 suggested that an increased serum IgA level was rather a consequence than a cause of atherosclerosis. The fact that IgA levels decreased in the post-transplant period only in patients with previous CA may corroborates this hypothesis. However, other factors also seem to contribute to the high serum IgA levels in patients with terminal heart failure, considering that these levels were also higher in patients without CA in comparison with those of healthy controls. In addition, the levels of IgA observed in the patients with CA evaluated in the present study were apparently higher than those observed by other authors8 in patients with atherosclerosis but without terminal heart failure (median values of 464 and 323 mg/dl, respectively). The nature of the other factor(s) responsible for the increase in serum IgA levels remains to be elucidated.
The observation of high pre-transplant serum IgA levels prompted us to determine the IgM and IgG concentrations in the same sera and the results showed higher IgG and IgM levels as compared to sera from healthy controls. In contrast to the post-transplant decrease in IgA levels in patients with CA, no differences were detected between pre- and post-transplant serum IgM or IgG levels. No correlation was found concerning pre-transplant IgG or IgM serum levels and the graft outcome in terms of one-year graft survival or the occurrence of rejection episodes during the first 6 months post-transplant (data not shown).
Although the present study is apparently the first to document an important increase in total serum IgA, IgM and IgG levels in candidates for heart transplant, there are reports in the literature concerning increased serum IgG and IgM levels in various cardiovascular diseases, such as hypertension9 and ischemic heart disease,10,11 and increased serum IgA levels in subjects with atherosclerosis8 or with previous myocardial infarction or other major ischemic events12. It should be noted that in the present study Ig levels were increased independently of patients’ basic disease (data not shown).
In conclusion, we did not detect any relationship between pre-transplant serum IgA, IgG or IgM concentration and cardiac allograft outcome, whereas we have documented an important increase of IgA, IgM and IgG in the sera of candidates for cardiac transplant. These levels remained unchanged during the post-transplant period, except for a dramatic decrease of IgA levels in patients who presented coronary atherosclerosis in the native heart. It would be interesting to evaluate the serum IgA levels of cardiac transplant recipients on long-term basis in order to investigate whether these levels may rise with the development of graft atherosclerosis, which seems to be a manifestation of chronic rejection.
Muscari A, Bozzoli C, Puddu GM, et al. Increased serum IgA levels in subjects with previous myocardial infarction or other major ischemic events. Cardiology 1993;83:383-389.