Atypical cells with abundant lacey cytoplasm seen in a patient with mononucleosis are most likely derived from which type of cells?

In the context of infectious mononucleosis, particularly when caused by Epstein-Barr virus (EBV), the atypical lymphocytes observed in a patient’s blood smear are primarily reactive T lymphocytes. During mononucleosis, the immune system responds to the viral infection by activating T lymphocytes, particularly CD8+ cytotoxic T cells. These activated T cells often exhibit morphological changes, which include a larger size, abundant cytoplasm, and a "lacy" appearance due to the presence of cytoplasmic granules and nucleoli.

While B lymphocytes are the original target cells for EBV, the atypical lymphocytes associated with the immune response to the infection reflect the activation and proliferation of T lymphocytes. Since the question specifically asks for the origin of the atypical cells with lacey cytoplasm seen in this clinical scenario, the correct answer identifies T lymphocytes as the source of these cells during the course of the infection.