You will recall the architecture of the normal lymph node includes a limiting connective tissue capsule, a cortex containing the follicles (mainly B lymphocytes) and a paracortical zone containing large numbers of T lymphocytes, a few immunoblasts and histiocytes. The medullary cords contain a mix of lymphocytes and plasma cells. Afferent lymphatics drain into the subcapsular sinus, branch into the cortical and paracortical areas, and converge in the hilar region to exit via the efferent lymphatics.

At the right is a secondary follicle. The central pale area of the secondary follicle is the germinal center.

The germinal center is ringed by a mantle of small lymphocytes similar to those seen in a primary follicle or unstimulated follicle.

Most of the lymphocytes, both large and small, in the mantle zone and the germinal center, are B lymphocytes, although a few T lymphocytes are scattered about.

Notice that the germinal center region is paler toward one pole. That is where the large, dividing cells are located. This pale zone points toward the stimulatory source, generally the capsular sinus. Note that the mantle zone is wider toward the stimulus.

The following is a brief review of the various morphological features that allow for the identification of lymphocytes and for the classification and diagnosis of lymphomas.

The morphologic description of lymphocytes is based on cell size, chromatin pattern, and the presence or absence of nucleoli.

Lymphoblasts are intermediate sized cells with round/oval nuclei which may be convoluted, fine chromatin, inconspicuous nucleoli, and scanty cytoplasm.

Normally lymphoblasts are found in the bone marrow and thymus.

Small cleaved lymphocytes (SCL) are small cells with angulated, clefted nuclei, clumped chromatin, absent nucleoli, and scant cytoplasm.

Large cleaved lymphocytes (LCL) are large cells with indented nuclei, vesicular chromatin absent/inconspicuous nucleoli, and moderate cytoplasm.

Large noncleaved cells (LNCL) are large cells with round/oval nuclei, vesicular chromatin, distinct nucleoli, and moderate cytoplasm.

Immunoblasts are larger than large noncleaved lymphocytes, with nucleoli that are especially prominant. They have abundant cytoplasm, often with plasmacytoid features.

Plasma cells (PC) are small-moderate sized cells with round nuclei, peripherally clumped chromatin and a prominent cytoplasmic "hof" or Golgi region.

In another proposal of B cell differentiation (Lukes & Collins,1974), virgin or resting SL transform to SCC; to LCC; to SNCC; to LNCC, to immunoblasts, and to PCs and memory B lymphocytes.