Question

Those strange gamma/delta T cells differ from the more typical and common alpha/beta T cells in which ways (circle all that apply):

-They are the more common type of T cell receptor in adults

-They do not need the CD3 chains to interact with their TCRs

-They may occur earlier in fetal development than alpha/beta T cells

-They always express high levels of CD4 and CD8, even when mature

Answer 1

Vertebrates contain two broad categories of T cells that are TCR α and β receptor chains γ and δ receptor chains. In case of adaptive immune response TCRαβ cells are dominant participants in the secondary lymphoid organs. But TCRγδ cells also play an important role in protecting our mucosal tissues from outside infection. TCRγδ are the first T cells that arise during fetal development. So, it provides the major protection even prior to birth. In many studies it was observed that γδ T cells are required to protect very young mice against the protozoal pathogen that causes coccidiosis. But the production of γδ T cells ceases after birth, and the TCR γδ T-cell population becomes only 0.5% of all mature thymocytes in the periphery of an adult animal.

So, the TCRαβ cells are the more common type of T cell receptor in adults not the TCRγδ. But TCRγδ may occur earlier in fetal development than alpha/beta T cells.

T cell receptor requires an association of CD3 to form the TCR-CD3 complex, this accessory molecule participates in signal transduction when the T cell encounters an antigen. This CD3 expression is required for membrane expression of αβ and γδ T-cell receptors. So, γδ cells need the CD3 chains to interact with their TCRs.

The γδ cells do not express either CD4 or CD8 co-receptors and do not recognize MHC molecules. Because, during the stage of thymocyte development they do not go through the DP (double positive) and leave the thymus as mature DN (double negative) T cells.