Reactive Lymphocytes: Types and Causes

What is a reactive Lymphocytes?

Reactive lymphocytes are lymphocytes that become large as a result of antigen stimulation. Typically they can be more than 30 µm in diameter with varying size and shape. The nucleus of a reactive lymphocyte can be round, elliptic, indented, cleft or folded. The cytoplasm is often abundant and can be basophilic.

Reactive vs neoplastic?

Reactive lymphocytes should be distinguished from neoplastic hematopoietic cells. This is particularly the case when the cells in question are large or “big blue” cells. Refer to the diagnostic algorithm and table in the related links below for help to determine if a large mononuclear cell with blue cytoplasm is a reactive lymphocyte or a neoplastic “blast”.

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Atypical lymphocyte refers to unusual structure of lymphocytes that are a part of the cell mediated immune system of the body. Also referred to as reactive lymphocytes, atypical lymphocytes are larger in size with a diameter of more than 30 microns. The large size of the lymphocytes is attributed to antigen stimulation.

There are several factors that are responsible for atypical lymphocytes.

These atypical lymphocytes are either folded, round, indented or elliptic in shape. They have basophilic cytoplasm and contain several vacuoles. In general these lymphocytes are gray, deep blue or pale blue in color. They are often found in association with a viral or a protozoan infection in the body.

Large Lymphocytes and Reactive Lymphocytes

Large lymphocytes have abundant pale blue transparent cytoplasm. If you imagine putting a printed page behind the cell, the cytoplasm looks as though you could see through it to read the words. Although there are usually no cytoplasmic granules present, a few large well-defined azurophilic granules (lysozomes) can occasionally be seen. In this case, the cells would be called large granular lymphocytes. A large lymphocyte can be found in the upper image to the right.

Reactive, or atypical, lymphocytes are relatively fragile cells, and as a result can be squeezed out of shape by surrounding cells, giving them a scalloped appearance instead of a smooth cytoplasmic edge. The nucleus of the reactive lymphocyte is larger than that of the small lymphocyte, and is more irregular in shape. Sometimes it is rounded, oval or indented with a typical “stretched” appearance. A reactive lymphocyte can be seen in the lower image to the right.

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