The type of lymphocyte which is predominent in chronic lymphatic leukemia –
**Core Concept**
Chronic lymphocytic leukemia (CLL) is a type of cancer characterized by the clonal proliferation of mature lymphocytes in the bone marrow, lymphoid tissues, and peripheral blood. The disease is primarily associated with a specific subtype of lymphocytes that have distinct morphological, immunophenotypic, and functional features.
**Why the Correct Answer is Right**
The predominant lymphocyte type in CLL is the **small mature lymphocyte**, also known as the **CD5+ B cell**. These cells express the CD5 antigen on their surface, which is a marker of activated B cells. CLL cells also typically express other surface antigens such as CD19, CD20, and CD23, but lack the expression of CD25 and HLA-DR. The CD5+ B cells in CLL are thought to arise from a subset of mature B cells that have undergone antigen-driven selection in the germinal center.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CLL is not primarily characterized by the proliferation of T cells. While T cells can be present in CLL, the disease is not defined by their presence.
**Option B:** This option is incorrect because CLL is not a disease of immature or immature-like lymphocytes. CLL cells are mature lymphocytes that have undergone antigen selection and have the typical morphology of small mature lymphocytes.
**Option C:** This option is incorrect because CLL is not associated with the proliferation of natural killer (NK) cells. NK cells are a distinct subtype of lymphocytes that have a different morphology and immunophenotype compared to CLL cells.
**Clinical Pearl / High-Yield Fact**
CLL is often associated with a variety of clinical features, including splenomegaly, lymphadenopathy, and autoimmune cytopenias. Patients with CLL may also have an increased risk of developing secondary malignancies, particularly lymphomas and leukemia.
**Correct Answer:** C.