Abstract 200

Objective: In earlier studies we have shown that 4 month old breastfed infants had a larger thymus than formula fed. The aim of this study was to relate the number of CD4+ and CD8+ T-lymphocytes in peripheral blood to the thymic size, and to analyse the association between breastfeeding, the distribution of T-lymphocytes, and thymic size in older infants.

Methods: A total of 50 healthy 8 month old infants, all partially breastfed, had an ultrasound scan of the thymus. All were examined again at 10 months of age. At both examinations the distribution of the CD4+ and CD8+ cells was measured in 37 infants, and the absolute count of T-lymphocytes were analysed in 34 of those.

Results: In the 34 infants still breastfed at the age of 10 month the thymus was larger than in the infants who had stopped breastfeeding in-between (p=0.05). We observed a significant increase in the number of CD8+ cells between 8 and 10 months. There was also an increase in the number of CD4+ cells, which was highly correlated to the number of breast-feedings at 8 months (p=0.002). This was reflected in the CD3+ count (the sum of CD4+and CD8+) (p=0.003). A larger thymic size at 8 months was associated with a higher CD8+ count at 10 months of age (p=0.009).

Conclusion: In a group of 8 - 10 month old infants breastfeeding was associated with a larger thymus and also influenced the number of T-lymphocytes. Our findings suggest that the link between the cellular immune function and breastfeeding remains during later infancy.