Thymus

Composed of epithelial cells (endoderm, important for T lymphocyte differentiation), Hassall corpuscles (regressed epithelial cells), T cells of varying phenotypes; B cells in thymic medulla and thymic perivascular space (increase with age, Hum Pathol 2001;32:926); also interdigitating reticulum cells, Langerhans cells, mast cells, eosinophils, stromal cells

Dendritic cells modulate autoimmune regulation through tissue restricted antigens (TSA) and promote central tolerance in thymus (Am J Pathol 2010;176:1104)

Wnt4 regulates thymic cellularity through expansion of thymic epithelial cells and early thymic progenitors.