In Patients with Hyper IgM Syndrome, There Is a Genetically

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.