T-cell activation begins when a/n presents an antigen fragment in association with an MHC-II molecule to a helper T cell. Once activated, helper T cells can differentiate into T helper 1 cells which will activate cells and secretes IL-2 to help activate cell-mediated immunity. CD4 helper T cells may also differentiate into T helper cells for B-cell activation, or T helper or T regulatory cells for modulation of the response. An APC may also activate a CD8 T cell when the antigen is complexed with . These CD8 cells are called T cells. Activated CD8 cells will mount a direct attack on target cells through the action of , which punch holes in membranes, and , which then enter through these passageways.

Which of the following is the primary activation signal to fully activate T helper cells?ANSWERThe TCR/MHC/antigen interaction is assisted by CD8 on the surface of T helper cells.The B7 protein on the APC cell surface interacts with CD28 on the surface of T helper cells.The TCR of the T helper cell interacts with the MHC I–antigen complex.The T-cell receptor (TCR) of the T helper cell interacts with the MHC II–antigen complex.

Similar to the need for a primary activation signal to fully activate T helper cells, a primary activation signal is needed to activate B cells by T-dependent antigens. Which of the following serves as the primary activation signal?ANSWERAn extracellular antigen binds to a B cell receptor.Cytokines are released upon proper T helper cell binding.The antigen enters the cell by endocytosis and is processed, and epitopes are displayed on the cell surface by MHC II.The MHC II–antigen complex on the B cell surface is bound by a T helper cell that can recognize the presented epitope.

An activated T helper cell becomes either an effector T helper cell or a memory T helper cell. What is the function of the effector T helper cell?ANSWER“Remember” the specific antigen and respond next time it is encounteredDestroy infected cells, cancer cells, and transplanted tissueRelease factors that help T cytotoxic cell and B cell activationRelease antibodies

__________ are the most abundant T cells, and their function is to __________.ANSWERT helper cells (CD4+); activate B cells to stimulate the humoral branch of adaptive immunityT cytotoxic cells (CD8+); directly destroy cells that are virus-infectedT helper cells (CD4+); coordinate the adaptive immune responseT cytotoxic cells (CD8+); seek and destroy cancer cells

CD8 is a marker of:Select one alternative:An activated macrophageB cellsCytotoxic T cellsHelper T cells