In Patients with Hyper IgM Syndrome,there Is a Genetically Based

Multiple Choice

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.