Complete but not partial thymectomy in early infancy reduces T-cell-mediated immune response: three-year tracing study after pediatric cardiac surgery.

Objective: Thymectomy is often performed to secure an operative field in surgery for congenital heart defects in early infancy. However, how neonatal thymectomy affects the subsequent development of the immune system in humans remains unclear. We monitored patients for 3 years from the time of thymectomy that was performed during cardiac surgery in early infancy.

Methods: For up to 3 years, we monitored the number of circulating lymphocytes and the clinical course of the children who underwent complete (n = 17), partial, and no (n = 15) thymectomy during congenital heart defect surgery performed at less than 3 months of age. The titers of immunoglobulin-G produced in response to vaccinated viruses and phytohemagglutinin responses were also measured.

Results: Six months after surgery, the number of T cells, including CD4(+) and CD8(+) subpopulations, decreased in patients with complete but not partial thymectomy. The reduction in T-cell number persisted for 3 years, whereas the number of B cells did not change. In patients with complete thymectomy, the titers of immunoglobulin-G produced in response to vaccinated measles and rubella viruses were reduced, whereas the phytohemagglutinin-induced proliferation of T cells was not impaired. In addition, hospitalization frequency associated with infectious diseases increased in patients with complete but not partial thymectomy.

Conclusions: The results revealed that complete thymectomy in early infancy reduces the number of circulating T cells and T-cell-mediated immune responses for at least 3 years, suggesting that the thymus should be at least partially preserved during surgery in early infancy to maintain protective immunity.