In patients with hyper IgM syndrome, there is a genetically based deficiency in expression of CD40 ligand. In addition to defects in antibody isotype switching, these patients have defects in T cell-mediated immune responses and become infected with intracellular parasites. Which one of the following normal functions of CD40 ligand is important in T cell-mediated immunity?
A)CD40-dependent isotype switching is required to produce antibody isotypes that activate T cells.
B)CD40 ligand is required for CTL killing of CD40-expressing infected cells.
C)CD40 ligand is required for maturation of CD4⁺ T cells in the thymus.
D)CD40 ligand on activated T cells binds to CD40 on antigen-presenting cells (APCs), and this enhances the expression of B7-1, B7-2, and cytokines by the APCs.
E)CD40 ligand on T cells binds to B7-1 and B7-2 on APCs, and this enhances the function of the APCs.

Question

Quizplus · Accepted Answer

CD40 ligand, a membrane-bound protein in the tumor necrosis factor (TNF) family of proteins, is expressed after T cell activation. When it binds to its receptor CD40, a TNF-receptor family member expressed on macrophages, and other antigen-presenting cells, signals are transmitted that enhance costimulator and cytokine expression (as well as other functions of macrophages). This serves to amplify the T cell response and enhance the killing of microbes ingested by macrophages. Antibodies are not required to activate T cells. CD40 does not transduce pro-apoptotic signals. CD40 ligand is not involved in T cell maturation and does not bind to B7-1 or B7-2.

In Patients with Hyper IgM Syndrome, There Is a Genetically