Lymphoid tissue and organs contain a lot of lymphocytes and other white blood cells.
The primary lymphoid organs include the thymus and bone marrow.
This organ is most active during childhood, reaching its largest size around puberty, with a weight of approximately 30 to 40 grams.
This process, along with regulatory T cells help prevent autoimmunity.
This is a low power image of a neonatal thymus.
At this magnification, the thin collagenous capsule is a little hard to see, but if we zoom in a little further, we can see the capsule more clearly, as well as the connective tissue that extends inward from the capsule into the thymus, forming incomplete lobules.
The lobules of both adult and neonatal thymi have inner regions that stain light purple and pink, which is called the thymic medulla; and the outer regions of the lobules are more basophilic or dark purple, which represents the cortex of the thymus.
The clear distinction between the inner medulla and outer cortex of each lobe is typically more prominent in early childhood, similar to the image on the right of the neonatal thymus.
If we look at the thymic cortex at high magnification, we see that the dark purple color of the cortex is mainly from densely packed and very basophilic T lymphoblasts, which are also called thymocytes.