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
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
The morphologic description of lymphocytes is based on
cell size, chromatin pattern, and the presence or absence of
Small lymphocytes (SL) are small cells
with round nuclei, clumped chromatin, absent
nucleoli, and scant cytoplasm; may have
plasmacytoid features,ie. peripherally clumped
Small noncleaved lymphocytes (SNCL) are
intermediate sized cells with round nuclei,
prominant multiple nucleoli and moderate cytoplasm,
sometimes with cytoplasmic vacuoles.
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
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
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.
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