Haematology: atypical lymphocytes in infectious mononucleosis: practice question

A Pathology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Pathology · Haematology: atypical lymphocytes in infectious mononucleosis

Sample item

A 19-year-old student has fever, exudative pharyngitis, posterior cervical lymphadenopathy and splenomegaly. The blood film shows lymphocytosis with large cells having abundant basophilic cytoplasm and indented nuclei. What are these atypical lymphocytes?

AEBV-infected plasma cellsBReactive CD8 positive cytotoxic T cellsCImmature TdT positive lymphoblastsDNeoplastic CD5 positive B cells

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Reactive CD8 positive cytotoxic T cells

In infectious mononucleosis, EBV infects B cells and the vigorous cytotoxic T-cell response against them produces the atypical lymphocytes on the film. The process is self-limited and polyclonal.

Option by option

A. EBV-infected plasma cells
EBV infects B cells and nasopharyngeal epithelium, and the circulating atypical cells are not infected plasma cells.
B. Reactive CD8 positive cytotoxic T cells (correct)
Correct. The atypical cells are reactive CD8 T cells responding to EBV-infected B cells.
C. Immature TdT positive lymphoblasts
TdT positive lymphoblasts define acute lymphoblastic leukaemia, which would show cytopenias and few mature lymphocytes.
D. Neoplastic CD5 positive B cells
CD5 positive B-cell proliferation describes chronic lymphocytic leukaemia, a disease of older adults.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Pathology question

What is the answer to this Pathology question?

The best answer is B, Reactive CD8 positive cytotoxic T cells. In infectious mononucleosis, EBV infects B cells and the vigorous cytotoxic T-cell response against them produces the atypical lymphocytes on the film.

Why is "EBV-infected plasma cells" not the answer?

EBV infects B cells and nasopharyngeal epithelium, and the circulating atypical cells are not infected plasma cells.

Why is "Immature TdT positive lymphoblasts" not the answer?

TdT positive lymphoblasts define acute lymphoblastic leukaemia, which would show cytopenias and few mature lymphocytes.

Why is "Neoplastic CD5 positive B cells" not the answer?

CD5 positive B-cell proliferation describes chronic lymphocytic leukaemia, a disease of older adults.

What concept does this question test?

It tests Haematology: atypical lymphocytes in infectious mononucleosis in Pathology. The process is self-limited and polyclonal.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Haematology: atypical lymphocytes in infectious mononucleosis?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.