Medical Laboratory Scientist (MLS) ASCP Practice Exam

The CD5 antigen is primarily found on mature T cells. CD5 is a surface protein that plays a role in T cell activation and differentiation. Its expression is a key feature of T cells, aiding in their identification in laboratory settings. Although CD5 can also be expressed on a small subset of B cells, it is predominantly associated with T cells and is especially noted in the context of certain T cell malignancies, such as T cell chronic lymphocytic leukemia.

In the case of plasma cells, natural killer cells, and memory B cells, CD5 is not a defining marker. Plasma cells are dedicated antibody-secreting cells that do not express CD5. Natural killer cells are a vital part of the innate immune response but do not express CD5. Memory B cells, which are critical for quick and effective responses to previously encountered antigens, also do not typically express CD5 as a characteristic marker. Thus, the identification of CD5 as a marker on mature T cells highlights its importance in immunology and assists in understanding the distinct roles and characteristics of various lymphocyte populations.