Question

Which of the following cell types exit thymus? a. CD3-CD4-CD8- cells b. CD3+CD4+CD8+ cells c. CD3+CD4+CD8- cells d. CD3+CD4-CD8+ cells e. CD3+CD4+CD25- cells f. CD3+CD4+CD25+ cells

Short answer

a. CD3-CD4-CD8- cells b. CD3+CD4+CD8+ cells c. CD3+CD4+CD8- cells d. CD3+CD4-CD8+ cells e. CD3+CD4+CD25- cells f. CD3+CD4+CD25+ cells Answer: c, d, e, and f (CD3+CD4+CD8- cells, CD3+CD4-CD8+ cells, CD3+CD4+CD25- cells, and CD3+CD4+CD25+ cells)

Step-by-step solution

Understanding the role of the thymus

The thymus is an important organ in the immune system, responsible for the maturation and development of T cells. Precursor T cells enter the thymus as immature cells and then undergo a series of developmental stages to become mature T cells capable of recognizing and responding to foreign antigens. Once mature, T cells exit the thymus and circulate in the peripheral blood and lymphatic system.

Identifying key T cell markers

T cells are characterized by the presence of specific cell surface markers, including the CD3, CD4, CD8, and CD25 molecules. In general, fully mature T cells will have one of two main phenotypes: helper T cells (CD3+CD4+CD8-) or cytotoxic T cells (CD3+CD4-CD8+). These mature T cells then exit the thymus to perform their immune functions in the periphery.

Going through each cell type

Now, let's go through each option provided and determine if they are mature T cells that exit the thymus: a. CD3-CD4-CD8- cells: These cells lack the CD3 marker, which is a critical signaling component of the T cell receptor. Therefore, these cells are not mature T cells and would not exit the thymus. b. CD3+CD4+CD8+ cells: These cells express all three markers, which is indicative of an intermediate stage during T cell development. These cells are not fully mature and would not exit the thymus. c. CD3+CD4+CD8- cells: These cells express the CD3 and CD4 markers, but not CD8, indicating they are helper T cells. These cells are considered to be fully mature T cells and exit the thymus. d. CD3+CD4-CD8+ cells: These cells express the CD3 and CD8 markers, but not CD4, indicating they are cytotoxic T cells. These cells are considered to be fully mature T cells and exit the thymus. e. CD3+CD4+CD25- cells: These cells express the CD3 and CD4 markers, but not CD25. Since CD25 is not required for a T cell to be considered mature, these cells can be considered as mature helper T cells and exit the thymus. f. CD3+CD4+CD25+ cells: These cells express the CD3, CD4, and CD25 markers. CD25 is a marker for regulatory T cells, which are a subset of helper T cells. These cells are considered to be fully mature T cells and exit the thymus.

Identifying the correct answer

Based on the analysis of each cell type, the following cell types exit the thymus: c. CD3+CD4+CD8- cells (helper T cells) d. CD3+CD4-CD8+ cells (cytotoxic T cells) e. CD3+CD4+CD25- cells (helper T cells) f. CD3+CD4+CD25+ cells (regulatory T cells)