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* Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73190;
Department of Pediatrics, New England Medical Center, Boston, MA 02111;
Department of Tropical Medicine and Medical Microbiology, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 96822;
Department of Pediatrics, University of Colorado Health Sciences Center, Denver, CO 80262; and
¶ Department of Pediatrics, National Jewish Medical and Research Center, Denver, CO 80206
| Abstract |
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| Introduction |
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(10), TNF-
(11), or IFN-
(12) but not against
unstimulated endothelial cells. Therefore, it has been postulated that
immune reactivity to vascular endothelium may contribute to the
vasculitis associated with acute KS. The etiology of immune activation in acute KS is not certain, although evidence supports an infectious etiology. Microbiologic data suggest a role for staphylococcal and streptococcal superantigens (13, 14). Furthermore, the clinical symptoms of KS share a number of features with staphylococcal and streptococcal diseases, such as toxic shock syndrome and scarlet fever. Superantigens have also been reported to induce the production of autoantibodies such as rheumatoid factor (15).
Autoantibodies against myosin have been implicated in the pathogenesis of rheumatic carditis and autoimmune myocarditis, diseases which also affect heart valve tissue and myocardium (16, 17). Furthermore, cardiac myosin is known to induce myocarditis in animal models (18). To date, there have been no studies examining the occurrence of anticardiac myosin autoantibodies in acute KS. Sera were also obtained from eight children presenting with acute rheumatic fever (ARF). The purpose of the current study was to seek evidence for antimyosin Abs in patients with acute KS.
| Materials and Methods |
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The study was conducted on sera from 13 children in the acute
phase of KS. These patients fulfilled the established clinical criteria
for KS (19). These criteria included a fever for
5 days
and at least four of the five following symptoms: nonexudative
conjunctival injection; changes in the oral pharynx, including mucosal
erythema, dry fissured lips, and "strawberry tongue"; changes in
the extremities, characteristically erythema of the palms and soles,
induration of the hands and feet, or perungual desquamation in the
subacute phase of the disease; polymorphous rash; and cervical
adenopathy (one or more nodes of
1.5 cm in diameter). A total of 11
of the 13 KS patients had clinical evidence of myocarditis during the
acute phase of their illness. Sera were also obtained from 12
age-matched febrile children, 10 normal adults who had no known
illness, and 14 children presenting with ARF. All ARF patients
demonstrated positive anti-streptolysin O titers and fulfilled the
revised Jones criteria for diagnosis of ARF. Informed consent was
obtained from each patient and/or their parents before the study.
Antigens
Human cardiac myosin was purified as described previously (20); the light meromyosin (LMM) peptides of human cardiac myosin were synthesized using a fluorenylmethoxycarbonyl strategy (21) and purified by HPLC. Sequences of the LMM peptides are indicated in Table I.
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ELISA and Western immunoblot technique
Microtiter plates were coated at 4°C overnight with purified
human cardiac myosin or LMM peptides at 10 µg/ml in 0.1 M
carbonate-bicarbonate coating buffer (pH 9.6). The plates were washed
with PBS Tween 20 and blocked with 1% BSA for 1 h at 37°C. The
plates were washed again with PBS Tween 20, and 50-µl serum dilutions
beginning at 1/250 were added to the microtiter wells. Sera were
diluted 2-fold in PBS. Serum dilutions were incubated overnight with Ag
at 4°C, and all tests were performed in duplicate. The plates were
washed again with PBS Tween 20, and goat anti-human IgM
(µ-chain-specific), IgG (
-chain-specific), and IgA
(
-chain-specific) conjugated with alkaline phosphatase (1/250
dilution) was added in 50 µl amounts to the microtiter plates and
incubated at 37°C for 1 h. Conjugated Igs were obtained from
Sigma. Next, the plates were washed with PBS Tween 20, and 50 µl of
the substrate para-phenyl-phosphate (Sigma 104) in diethanolamine
buffer was added to the wells. OD was measured at 410 nm in an ELISA
plate reader (Dynatech, Chantilly, VA). Titers were calculated from the
0.30-OD endpoint in the ELISA.
Western blots were performed as described previously (17). Briefly, 8 µg of purified human cardiac myosin was loaded into wells of an SDS polyacrylamide gel and electrophoresed until the tracking dye reached the bottom of the gel. The gel was blotted onto a nitrocellulose membrane using a blotting apparatus (Bio-Rad, Hercules, CA). The blot was blocked with 3% milk for 1 h at 37°C. Sera from control subjects and KS patients were diluted 1/1000 in PBS. A section of the blot was used to stain the cardiac myosin heavy chain with a molecular mass of 200 kDa. Nitrocellulose strips containing the human cardiac myosin protein band were cut and reacted separately with each of the patient sera and with rat anti-human cardiac myosin sera at 1/1000. The control sera recognized the 200-kDa myosin heavy chain. The strips were washed five times with PBS Tween 20 and reacted with the secondary Ab conjugate goat anti-human polyvalent Igs conjugated with HRP. The blot was developed using chloronaphthol as indicator with hydrogen peroxide as substrate as described previously (17). The serum reaction with the human cardiac myosin heavy chain was scored as 04+ as compared with a 4+ reaction by the positive control anti-rat human cardiac myosin and a PBS-conjugated secondary Ab control that was negative or 0 reactivity.
51Cr release assay
A primary rat heart cell line (no. CRL-1446, American Type Culture Collection, Manassas, VA) was plated into 96-well tissue culture plates at 1 x 104 cells/well in IMDM with 20% FBS. The heart cells were incubated at 37°C and in 5% CO2. A total of 5 µCi of 51Cr was added per well and incubated at 37°C for 2 h. The cells were washed in the IMDM containing 20% FBS, and 100 µl of IMDM plus 20% FBS was added to each well and incubated at 37°C for 1 h. Sera from patients with KS and control sera were diluted 1/5 in IMDM. Plates were washed with serum-free IMDM three times, and 100 µl of diluted serum was added to wells in triplicate. Negative control wells received 100 µl of IMDM; maximum release wells received 100 µl of 1N HCL. Positive control wells received human and mouse mAbs that were cytotoxic for the heart cell line. Once the test sera were added, plates were incubated at 37°C for 45 min and 100 µl of freshly prepared guinea pig complement was added. After a 1-h incubation at 37°C, the supernatants were harvested by a Skatron harvester (Lier, Norway) and counted on an LKB compugamma counter (Uppsala, Sweden). The formula used to calculated percent lysis is as follows: ([test cpm - spontaneous release cpm]/[maximum release cpm - spontaneous release cpm]) x 100. Spontaneous release was determined as cpm from the IMDM negative control samples without complement.
Statistics
Means with SDs were calculated for the KS and control sera groups; the means of the sera groups were compared by the unpaired Students t test to determine significance, which was calculated as two-tailed p values.
| Results |
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To investigate the possibility that immune responses to cardiac myosin were elevated in KS, sera from 13 patients with KS, 12 age-matched febrile controls, and 10 normal adults were reacted with purified human cardiac myosin by ELISA. Fig. 1 illustrates the stronger reactivity of a group of KS sera with human cardiac myosin in the ELISA as compared with sera from age-matched controls and normal adults. The figure shows a scattergram of individual serum titers when reacted with human cardiac myosin as Ag. Greater than 50% of KS sera had titers greater than the mean antimyosin titers in febrile control patients (Fig. 1). However, only 5 of 13 KS sera tested had higher titers. Titers of normal sera ranged from 500 to 8,000, whereas Ab titers against human cardiac myosin in KS patients ranged from 1000 to 64,000 (Fig. 1). The KS titers to human cardiac myosin as a group were significantly different from age-matched febrile controls (p = 0.047) and normal adult controls (p = 0.04). Only antimyosin IgM Ab titers are shown, because there was little or no difference observed between KS and age-matched control sera in their IgG reactivity to cardiac or skeletal myosins (data not shown). No antimyosin IgA Abs were detected in any of the sera. KS sera, some of which had high titers to human cardiac myosin, also reacted with skeletal myosin but consistently with lower titers. Thus, there is a group of KS patients that responds strongly to human cardiac myosin.
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To determine whether the KS sera that were highly reactive with human cardiac myosin would recognize peptide epitopes in the human cardiac myosin heavy chain, eight KS sera with elevated titers (titers = 64,000; 32,000; 32,000; 32,000; 16,000; 8,000; 8,000; and 2,000) to myosin were pooled and reacted with 49 LMM peptides in the ELISA. In addition, febrile age-matched control sera (titers = 1000; 1000; 1000; and 8000) were also pooled and reacted with the LMM peptides. The reactivity of the KS sera group with the LMM peptides is shown in Fig. 4A. LMM peptides 1, 18, 32, 34, 47, and 49 were the most reactive with KS sera after normal age-matched control sera reactivity was subtracted to obtain the final reactivity of the KS sera shown in Fig. 4A. The reactivity of the control sera ranged from an OD of 0.2 to 0.5 and was subtracted. These data are compared with the reactivity of a group of eight ARF sera reacted with the LMM peptides (Fig. 4B). The reactivities of the KS and ARF sera with the LMM peptides have similarities, but are also clearly different. The greatest differences are observed for LMM peptides 13 and 25, which are positive only in ARF, whereas peptide 47 was twice as reactive with KS sera. Because results using pooled sera may not reflect the individual serum reactivities, we tested nine KS and six ARF sera individually. Table III shows the results of these tests. Table III compares the reactivity of both KS and ARF sera with the LMM peptide panel. As underlined in the Table III, peptides positive with three or more sera in each group were underlined to highlight the reactivities of multiple sera with a particular peptide. The KS sera reacted with LMM-1, -4, -7, -16, -18, -32, and -43, whereas the ARF sera reactive with LMM-6, -7, -18, -19, -25, -29, -32, -36, and -47. However, normal sera did not react positively with any of the LMM peptides as shown in Table III. Comparison of data from pooled KS sera in Fig. 4A with the individual serum study indicated that the peptides identified on the pooled sera were similar to those identified in individual sera. Comparison of the ARF sera reacted with LMM peptides (Table III) and with the pooled sera (Fig. 4B) suggested that the data were quite similar. Some of the other LMM peptides recognized by two of six ARF sera and not considered mainstream were LMM-1, -4, -8, -16, -22, -28, -34, -35, -39, -40, -43, -45, and -49, which were also seen in Fig. 4B. The conclusion from these data is that both KS and ARF sera recognize different but some overlapping epitopes. In individual and pooled serum studies, LMM-6, -19, and -25 were unique to or seen more often in ARF than in KS. The LMM peptides seen frequently in both diseases were LMM-7, -18, -32, and -47.
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To further characterize the sera containing antimyosin Abs, the sera were tested for cytotoxicity against a rat heart cell line. KS-8 (ELISA titer = 8000) and KS-11 (ELISA titer = 32,000 and myosin blot 2+) sera produced 31% and 63% cytotoxicity, respectively. The cytotoxicity of normal sera ranged from 2 to 14%. These results were highly reproducible and did not necessarily correlate with anti-human cardiac myosin titers. However, the two patients with cytotoxic Abs had titers above the normal mean (Fig. 1). The strong cytotoxicity of KS-11 was particularly interesting in that this patient was documented to have features of myocarditis clinically at the time the acute sample was obtained. In addition, this patient recognized many of the LMM peptides as shown in Table III (one of nine for many LMM peptides not recognized by the other eight KS sera). Features for this patient included a gallop rhythm, a murmur tricuspid regurgitation, and sinus tachycardia. In addition, the patient had clinical features of congestive heart failure and required diuretic therapy. Clinical laboratory evidence included electrocardiogram changes of low voltage and T wave inversion that resolved in convalescence. The initial two echocardiograms demonstrated biventricular dysfunction, pericardial effusion, and normal coronary arteries. Subsequent echocardiograms demonstrated the development of diffuse aneurysms of the left main, left anterior descending, and right coronary artery. The myocardial function of this patient improved and returned to normal, as did her clinical features of myocarditis. She developed worsening ischemic heart disease over the next 6 mo. The patient went on to cardiac transplantation, and the explanted heart had evidence of coronary stenosis and patchy vasculitis as well as myocyte damage consistent with previous features of myocarditis and ischemic damage. This patient died 9 mo posttransplant after multiple severe episodes of acute rejection. To our knowlege, she is the only reported death posttransplant for a KS patient (23).
| Discussion |
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Myosin-reactive sera from acute KS patients were also examined for reactivity with a panel of 49 overlapping peptides that span the human LMM subfragment of cardiac myosin. Sera from acute KS patients had a different pattern of reactivity than sera from ARF patients, although some LMM peptides were recognized by both diseases. These data suggest that acute KS is associated with a specific Ab response to certain epitopes of human cardiac LMM. Strong LMM reactivity by a serum reflected a pattern of autoimmune heart disease (either rheumatic heart disease in ARF or myocarditis in KS). This LMM reactivity may indicate epitope spreading throughout the myosin molecule. Epitope spreading within and among autoantigens has been suggested in other autoimmune states (22). It is possible that the more peptides recognized, the greater the risk of developing pathogenic autoantibodies reactive not only with epitopes within the myosin molecule but with cross-reactive epitopes present at the cell surface extracellular matrix, or basement membrane. The presence of cytotoxic Ab in some of the KS sera suggests that this possibility exists. As for the diagnostic potential of the antimyosin or anti-LMM Abs in KS or ARF, we believe that they at least represent a relative risk factor and could be important in identifying patients predisposed to autoimmune heart disease.
Antimyosin Abs have been associated with a number of autoimmune states, including rheumatic fever and chronic autoimmune myocarditis (16, 18, 20, 24, 25, 26, 27). It is not clear what role these antimyosin Abs play in the pathogenesis of disease. However, it is known that antimyosin Abs deposit in the heart of susceptible animals that develop myocarditis (26), and antimyosin/antistreptococcal mAbs are cytotoxic for heart cells in culture (28, 29). In addition, antimyosin Abs recognize bacterial Ags such as the group A streptococcal M protein and N-acetyl-glucosamine, the dominant epitope of the group A streptococcal carbohydrate (17, 20, 24, 29, 30, 31, 32) as well as viral Ags such as the Coxsackie viral capsid proteins (29, 33). Although antimyosin Ab can be present in the sera of normal individuals (34), it is seen usually at low levels compared with disease (16).
Although depressed myocardial function and wall motion abnormalities
may be a manifestation of coronary injury and ischemia, it is unlikely
that this is the sole mechanism; only 20% of untreated KS patients
develop coronary artery lesions, yet over half have evidence clinically
for myocarditis. In addition, the myocardial depression seen is
reversible with i.v.
-globulin in the absence of coronary artery
involvement and does not correlate with the presence of coronary artery
lesions (7). Cytokines such as TNF-
and IL-6 have both
been reported to depress myocardial function (35, 36).
They as well as other cytokines are known to be elevated in acute KS
and could also contribute to the acute depressed myocardial
function.
The mechanism by which anticardiac myosin may contribute to acute myocarditis in KS is not known. Preliminary studies suggest that some of these sera may cause myocardial injury via their cytotoxic activity against heart cells. Cytotoxic Abs against vascular endothelium have been found previously in KS sera, and antimyosin mAbs that recognize cell surface epitopes or Ags such as laminin are cytotoxic for the rat heart cell line used in this study (24). However, currently there is no definitive explanation for the cytotoxicity of KS sera. Further studies are required to determine whether antimyosin Abs are able to depress myocardial function without causing frank cytolysis of cells. Nevertheless, our current studies open up a new avenue for investigation into the mechanisms of myocarditis in KS, one of the most common causes of acquired heart disease in childhood.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Donald Y. M. Leung, Department of Pediatrics, National Jewish Medical and Research Center, 1400 Jackson Street, Room K926, Denver, CO 80206. E-mail address: leungd{at}njc.org ![]()
3 Abbreviations used in this paper: KS, Kawasaki syndrome; ARF, acute rheumatic fever; LMM, light meromyosin. ![]()
Received for publication October 29, 1998. Accepted for publication May 10, 1999.
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-D-glucosamine and cytokeratin peptides: evidence for a microbially driven anti-keratin antibody response. J. Immunol. 152:4375.[Abstract]
-D-glucosamine. J. Immunol. 151:3902.[Abstract]
-D-glucosamine in reaction with antibodies and lectins, and induces in vivo anti-carbohydrate antibody response. J. Immunol. 153:5593.[Abstract]
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