Neonatal thymectomy: Does it affect immune function?

Objective: The purpose of this study was to determine whether thymectomy in the newborn has a negative effect on immune function. Methods: Twenty-five neonates (<30 days) who had thymectomy at congenital heart repair were prospectively studied to determine immune function. The percentage of T-cell subtypes including CD3 (all T cells), CD4 (helper T cells), and CD8 (suppressor T cells) was determined. In six patients, further testing of CD4 cells was done to determine whether they were newly formed, recent thymic emigrants (CD4, CD45, and RA(+)), or older educated lymphocytes (CD4, CD45, and RO+). Response to the mitogen phytohemagglutinin and to tetanus toroid were determined, as were antibody titers to tetanus. Samples were drawn before the thymectomy, at approximately 3 months after immunization and at 1 year. Ten age-matched control patients were tested. At follow-up, parents were asked about infections. Results: Prethymectomy T-cell subsets were all normal and comparable to controls. At 12 months, the percent of CD3 was significantly less than in the control group (48% +/- 3% versus 64% +/- 2% [mean + standard error of the mean]; p < 0.01) as was CD4 (31% +/- 2% versus 46% + 2% [mean +/- standard error of the mean];p = < 0.01). CD8 did not drop. Surprisingly, the percent of CD4 that were recent thymic emigrants did not decrease significantly (50% +/- 8% versus 60% +/- 6% [mean +/- standard error of the mean]; p = not significant). Lymphocyte blastogenesis to phytohemagglutinin and tetanus toroid and antibody to tetanus were all normal at 12 months. No patient required readmission for infection, and there were the expected number of minor infectious events (median 3; 95% confidence interval 1,4). Conclusion: Thymectomy in neonates results in a modest but significant decrease in T-lymphocyte levels, but there is no compromise in immune function.