Which one of the following statements about the molecules B7-1 and B7-2 is NOT true?
A)B7-1 and B7-2 expression on antigen-presenting cells (APCs)is upregulated by the presence of "danger" signals,such as lipopolysaccharide,as well as cytokines,such as interferon (IFN)-$\gamma$
B)B7-1 and B7-2 are expressed at low levels on some resting APCs.
C)Induction of B7-1 usually occurs before the induction of B7-2 in an immune response.
D)B7-1 and B7-2 bind to CD28 on T cells and provide "second signals" for naive T cell activation.
E)Activated helper T cells can induce expression of B7-1 and B7-2 on APCs via CD40L binding to CD40.

Question

Quizplus · Accepted Answer

The temporal patterns of B7-1 and B7-2 expression differ.B7-2 is expressed constitutively at low levels and induced early after activation of antigen-presenting cells (APCs),whereas B7-1 is not expressed constitutively and is induced hours or days later.The expression of B7-1 and B7-2 on APCs is induced by "danger signals" of infection.These signals are mediated by binding of lipopolysaccharide (LPS),unmethylated CpG DNA,and other ligands of Toll-like receptors.Signals mediated through cytokines,such as interferon (IFN)-$\gamma$,as well as through CD40 ligand,can also up-regulate B7-1 and B7-2 expression on APCs.Both B7-1 and B7-2 bind to CD28 on naive T cells,thus providing the second signal needed for activation of T cells.

Which One of the Following Statements About the Molecules B7-1 γ\gammaγ

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