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.

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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 Based