Normal resting lymphocytes
In normal blood, the most frequent appearance of a lymphocyte is as a “resting cell”. This means the cells are small (generally size is given as around 8-10µm which makes them a little larger than a red cell), typically they have a relatively thin rim of pale cytoplasm, and a nucleus with condensed chromatin (most commonly indented) and an indistinct or absent nucleolus. Normal lymphocytes however are not identical to each other, and have subtle differences in size, nuclear shape, or cytoplasmic volume
- B and T cells
In adults, lymphocytes should be fewer than 4x109/l (greater in children), with around 70% T cells and 20% B cells (up to 10% are NK cells). T and B cells cannot be confidently distinguished from each other based on morphology, although it is often assumed that the less regular forms are T cells.
Appearances may vary in terms of nuclear shape, cytoplasmic appearance or volume, but essentially the features of these cells are closely similar.
- Large granular lymphocytes
The LGL cells (specialised T cells or natural killer cells) have a distinctive appearance, but are the least frequent cells in normal circumstances forming less than 10% of lymphocytes (0.4x109/l).
Significantly larger than other normal lymphocytes with a "softer" less distinct chromatin, pale cytoplasm that often flows around red cells, and have characteristic large azurophilic granules in their cytoplasm.