**Core Concept**
Atypical lymphocytosis refers to the presence of abnormal-appearing lymphocytes in the peripheral blood, often seen in certain viral infections. This phenomenon is characterized by the proliferation of lymphocytes with morphological abnormalities, such as an increase in size, irregular nuclear shape, and cytoplasmic inclusions.

**Why the Correct Answer is Right**
In viral infections like infectious mononucleosis (caused by Epstein-Barr virus), the lymphocytes become activated and proliferate in response to the viral antigen. This leads to the formation of atypical lymphocytes, which are larger than normal lymphocytes and have irregular nuclear shapes and cytoplasmic inclusions. The correct answer is a classic example of a viral infection that causes atypical lymphocytosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because atypical lymphocytosis is not typically associated with bacterial infections like tuberculosis. While tuberculosis can cause lymphocytosis, the lymphocytes are usually of the normal type and not atypical.
**Option B:** This option is incorrect because autoimmune disorders like systemic lupus erythematosus (SLE) can cause lymphocytopenia, which is a decrease in the number of lymphocytes, rather than atypical lymphocytosis.
**Option C:** This option is incorrect because viral hepatitis can cause lymphocytopenia and an increase in atypical lymphocytes, but it is not the most likely cause of atypical lymphocytosis compared to infectious mononucleosis.

**Clinical Pearl / High-Yield Fact**
Infectious mononucleosis is often accompanied by fever, sore throat, lymphadenopathy, and splenomegaly, making it a classic presentation of atypical lymphocytosis.

**Correct Answer:** D. Infectious mononucleosis