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Bacillus Calmette-Guérin vaccination, thymic size, and thymic output in healthy newborns
Nina Marie Birk1, Thomas Nørrelykke Nissen1, Vera Zingmark1
1Department of Pediatrics, Copenhagen University Hospital, Hvidovre, Denmark.
Insights
Bacillus Calmette-Guérin (BCG) vaccination at birth did not alter thymic size. However, larger thymic size at birth correlated with more lymphocytes and fewer infections in infants.
Area of Science:
- Immunology
- Pediatrics
- Vaccinology
Background:
- The Bacillus Calmette-Guérin (BCG) vaccine is known for potential nonspecific benefits in infant health.
- Investigating BCG's impact on thymic size and its relation to immune function is crucial for understanding early-life immunity.
Purpose of the Study:
- To determine if BCG vaccination at birth affects thymic size in infants.
- To explore associations between thymic size, thymic output, lymphocyte counts, infection risk, and BCG vaccination.
Main Methods:
- Infants were randomized to receive BCG vaccination or no vaccination.
- Thymic index (TI) and thymic/weight index (TWI) were measured via ultrasound at birth and 3 months.
- T cell subpopulations (CD4+, CD8+, recent thymic emigrants) were analyzed using flow cytometry; infections were parent-reported.
Main Results:
- BCG vaccination did not significantly impact thymic size (TI) at 3 months.
- At birth, higher lymphocyte counts (including CD4+, CD8+, and recent thymic emigrants) were associated with larger thymic size (TI and TWI).
- A larger thymic size at birth was linked to a reduced risk of infections within the first 3 months of life.
Conclusions:
- BCG vaccination showed no discernible effect on thymic size.
- Thymic size, assessed by TI and TWI, may serve as a predictor of an infant's immunological capacity.
- The findings highlight the importance of thymic size in relation to lymphocyte production and protection against early-life infections.
Background:
The Bacillus Calmette-Guérin vaccine (BCG) has been associated with beneficial nonspecific effects on infant health. We aimed to examine the effect of BCG at birth on thymic size and the associations between thymic output, circulating lymphocytes, risk of infection, and thymic size.
Methods:
In infants randomized to BCG or no BCG, thymic index (TI), and thymic/weight index (TWI) were measured by ultrasound at birth and at the age of 3 mo. T cell subpopulations including CD4+ T cells, CD8+ T cells, and recent thymic emigrants (RTEs) were assessed by flow cytometry. Infections up to age 3 mo were parent-reported.
Results:
BCG vaccination did not affect thymic size at age 3 mo, measured as TI. At birth, the number of lymphocytes, CD4+ T cells, CD8+ T cells, and RTEs were positively associated with TI and TWI. Furthermore, a reduced risk of infections up to age 3 mo was associated with a large thymic size at birth.
Conclusion:
We found no effect of BCG vaccination on thymic size. The positive association between thymic output, lymphocytes, reduced risk of infections, and TI/TWI suggests that assessment of TI/TWI by ultrasound may be a predictor of the immunological capacity in the newborn.
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