Structure of the germinal centers in the chicken caecal tonsil: light and electron microscopic and autoradiographic studies.

The light and electron microscopic structure of the germinal center of chicken caecal tonsils were studied. Two kinds of germinal centers were revealed; the first was located deep in the lymphatic tissue close to the muscle layer of the caeca. These germinal centers frequently have an incomplete capsule, and are not, therefore, separated from the diffuse lymphatic tissue. The second kind of germinal center was located closer to the epithelium and had a complete capsule separating it from the diffuse lymphatic tissue. Both germinal centers possessed an outer dark cortical zone which contained smaller lymphoblasts (of less than 10 micron in diameter) and a central medullary area which contained larger lymphoblasts (up to 16 micron). Autoradiographic studies revealed that the small lymphoblasts of the outer cortical zone are concerned with cell generation and that the large lymphoblasts of the medullary area may have derived from the small lymphocytes. Within the medullary area of the germinal center are cells which are embedded in an intercellular substance of high density. We propose that the intercellular substance may be a product of this cell. For discussion purposes we have called this cell a secretory cell. The secretory cell may originate from a small lymphocyte-like cell.