A 13-year-old boy has leukemia with marked features suggesting T-lymphocyte transformation. What is the normal counterpart of these malignant lymphocytes?

In the context of the question, the normal counterpart of the malignant T-lymphocytes in leukemia, particularly a scenario that suggests T-lymphocyte transformation, would be the activated T lymphocytes.

In the immune system, T-lymphocytes develop from precursor cells in the bone marrow and eventually migrate to the thymus to mature. These mature T-lymphocytes can further differentiate into various subsets, including cytotoxic T cells (also known as CD8+ T cells) and helper T cells (CD4+ T cells), depending on the signals they receive.

When T-lymphocytes are activated, especially in response to an infection or in other immune challenges, they transform into effector T cells, which can directly kill infected cells or help coordinate the immune response. In cases of malignancy like T-lymphoblastic leukemia, the characteristics of these leukemia cells mirror the features of activated cytolytic effector T lymphocytes, as they are often associated with increased proliferation and abnormal function.

This understanding positions activated cytolytic effector T lymphocytes as the correct normal counterpart to the malignant T-lymphocytes described in the case. The other answer choices represent lineages or states of B-cells or early