A Level Biology Practice Exam

What type of lymphocyte is characterized by having CD4 receptors?

1. T regulatory cells

2. T killer cells

3. T helper cells

4. T memory cells

The correct answer is: T helper cells

T helper cells are characterized by the presence of CD4 receptors on their surface. These cells play a pivotal role in the immune system by assisting other cells in recognizing and responding to antigens. When activated by specific antigens presented by antigen-presenting cells, T helper cells secrete cytokines that stimulate the activity of various immune cells, including B cells and cytotoxic T cells. This activation is critical for coordinating an effective immune response, facilitating the production of antibodies by B cells and enhancing the cytotoxic activity of T killer cells. The presence of CD4 receptors specifically allows these cells to bind to MHC (Major Histocompatibility Complex) class II molecules, which are essential for the recognition of antigens and subsequent immune activation. Other types of lymphocytes mentioned, such as T regulatory cells, T killer cells, and T memory cells, have different roles and characteristics, notably pertaining to CD8 receptors or lacking a distinct function in the primary immune response and memory formation.