In addition to lymphocytes, macrophages, and epithelial cells, the bursa medulla possesses
a cell we have named the secretory cell. The secretory cell, which makes up approximately
0.5% of the bursal cell population, exhibits an eccentric nucleus with a chromatin
pattern similar to that of a small lymphocyte and an elongated cytoplasm with one
or more cell processes. The electron-dense cytoplasmic granules of the immature secretory
cell are localized around the cytocentrum, while in the mature secretory cell these
granules are situated beneath the cell membrane of one process. The granular location
endows a polarized appearance to the secretory cell. The surface of the membrane is
covered with a finely spotted flocculated substance, which may originate from a granular
discharge. The round, ovoid, or irregular-shaped granules reveal a homogeneous or
distinctive internal pattern. The cortico-medullary border may be the germinal layer
of the bursal medulla. The bursal secretory cell is a modified dendritic cell with
possible endocrine functions that may be important in B-cell induction.
