When activated by whatever means, lymphocytes can become very large (approaching or exceeding the diameter of monocytes) and basophilic (reflecting the increased amount of synthesized cytoplasmic RNA and protein). The cytoplasm becomes finely granular (reflecting increased numbers of organelles), and the nuclear chromatin becomes less clumped (the better to transcribe you with, my dear!). Such cells are called "transformed lymphocytes," "atypical lymphocytes," or "viral lymphocytes" by various votaries of blood smears. Although such cells are classically associated with viral infection (particularly infectious mononucleosis), they may also be seen in bacterial and other infections and in allergic conditions. A morphologic pitfall is mistaking them for monocytes (a harmless mistake) or leukemic blasts (not so harmless).
*Anatomy & Physiology by Philip Pack, PhD