The postnatal development of lymphoreticular aggregates and lymph nodes in infants' lungs.

A quantitative study has been made of standardized sections taken from the right middle lobe of 316 children's lungs. Lungs showing no pathological state showed that lymph nodes are present at birth and these increase in prominence if not in numbers throughout the first year after birth. Lymphoreticular aggregates are not present among the alveoli of the normal infant lung at birth. These first appear around a week after birth and progressively increase in number throughout infancy and early childhood, being almost universally present by the age of 5 years. The development of peripheral lymphoreticular aggregates in the lungs of infants appears to be entirely environmentally and antigenically stimulated.