J Thorac Cardiovasc Surg 1998;116:532-533
© 1998 Mosby, Inc.
Aortic valves are antigenic but less so than myocardium
B. B. Rajani, B,BS,
R. E. Mee, ChB, FRCS,
N. B. Ratliff, MD
Reply to the Editor
The pathologic findings in aortic valves by Kawauchi and associates
1 in heterotopic heart allotransplant primates are very interesting. They report mononuclear cell infiltration in 90% of donor aortic valves examined 8 to 27 days after transplantation. These findings are similar to the observations in our study, 2 in which failed homograft (allograft) cardiac valves removed from infants demonstrated lymphocytic infiltration in valve leaflets and aortic sleeves. 2 In contrast, Mitchell and coauthors, 3 who examined explanted cryopreserved homograft heart valves and valves removed from transplanted homograft hearts, found infiltration of valves by inflammatory cells to be absent or minimal. Although in Mitchell's study homograft valves were examined at many postoperative intervals, valves that were removed 9 days to 2 months after implantation were not studied because the specimens were unavailable. Furthermore, the valves that were explanted at 2 to 4 months (n = 3) did demonstrate a prominent inflammatory infiltrate, including neutrophils, macrophages, and T-lymphocytes. However, these valves had failed because of infective endocarditis; therefore, even if there was a component of the infiltrate that may have been related to a rejection process, this would have been impossible to prove. In Mitchell's study, if the valves that failed because of infective endocarditis are discounted, the potential temporal window during which it is possible that immunologically mediated injury could have occurred undetected would be between 9 days and 6 months. It is interesting that the valves in Kawauchi's study were examined 8 to 27 days after transplantation. This period almost fits into the aforementioned window of time. In our study, 2 mononuclear cell infiltrates were found in five infant cryopreserved homograft valves explanted after 6.5 to 31 weeks. It may be that this intermediate implant interval represents the peak time for cellular rejection of homograft valves, especially in the younger pediatric population.
We recently studied in detail nine homograft valves that were explanted from two children and seven adults whose ages ranged from 4 to 61 years. The time from valve insertion to removal in these patients ranged from 8 months to 23 years. In contrast to the homograft valves in infants, infiltration by mononuclear cells was not observed. We noted moderate to marked intimal hyperplasia (composed of spindle cells positive for smooth muscle actin) in seven of the nine non-infant homografts. The intimal proliferation was very similar to the intima in graft vascular disease in solid organ transplants. Assuming that graft vascular disease is a form of rejection, the hyperplastic intima in these allografts would then represent ongoing rejection. We continue to believe that allograft valves in any age group are not immunologically privileged.
Departments of Anatomic Pathology and Cardiothoracic SurgeryThe Cleveland Clinic Foundation,
Cleveland, OH 44195
References
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Kawauchi M, Tanaka K, Nakajima J, Takeda M, Oka T, Furuse A. Antigenicity of heart valves and vessels: a primate heart transplant study. Transplant Proc 1996;28:1824-5.[Medline]
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Rajani B, Mee RB, Ratliff NB. Evidence for rejection of homograft cardiac valves in infants. J Thorac Cardiovasc Surg 1998;115:111-7.[Abstract/Free Full Text]
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Mitchell RN, Jonas RA, Schoen FJ. Pathology of explanted cryopreserved allograft heart valves: comparison with aortic valves from orthotopic heart transplants. J Thorac Cardiovasc Surg 1998;115:118-27.[Abstract/Free Full Text]
