OSMT (Ontario Society of Medical Technologists) Practice Exam

Cytotoxic T cells become immunocompetent in the thymus. During their development, these lymphocytes undergo a selection process that ensures they can effectively recognize and respond to specific antigens presented by Major Histocompatibility Complex (MHC) molecules. This maturation process in the thymus is crucial, as it determines which cells are allowed to enter the peripheral circulation and participate in immune responses.

The other choices include B cells and plasma cells, which mature in the bone marrow rather than in the thymus. Suppressor T cells, also known as Regulatory T cells, are a subset of T cells that help regulate immune responses but also go through similar development in the thymus. However, the specific term "immunocompetent" often refers to the activation and differentiation of cytotoxic T cells that can directly kill infected or cancerous cells, thus emphasizing why cytotoxic T cells are the prime focus of this question.