Final answer:
The atypical lymphocytes found in patients with infectious mononucleosis are likely derived from B lymphocytes, since the Epstein-Barr virus, which often causes the disease, primarily resides in and activates these cells.
Step-by-step explanation:
The atypical lymphocyte seen in the peripheral smear of patients with infectious mononucleosis is most likely derived from B lymphocytes. Infectious mononucleosis, often caused by the Epstein-Barr virus (EBV), leads to the proliferation of atypical lymphocytes which are essentially B cells that have encountered the virus. EBV resides within B cells, and the body generates these atypical lymphocytes as a response to the infection. While both B and T cells are crucial to the adaptive immune response, it is typically B cells that are associated with the production of antibodies and therefore are the primary cells that become atypical in infectious mononucleosis.