Which of the following mechanisms does NOT contribute to the generation of a cytolytic T lymphocyte (CTL)response to a viral infection? A)Dendritic cells phagocytose infected cells or viral particles and present them to naive CD8⁺ T cells via the class I MHC pathway. B)Dendritic cells are infected with the virus and present viral peptides to naive CD8⁺ T cells via the class I MHC pathway. C)CTLs are directly activated by CD40L expressed on activated helper T cells through CD40. D)Helper T cells secrete cytokines,such as interleukin-2,that promote the proliferation and differentiation of CD8⁺ T cells. E)Helper T cells activate infected antigen-presenting cells (APCs)via the CD40 ligand-CD40 pathway,and the activated APCs present viral peptides to naive CD8⁺ T cells via the class I MHC pathway.

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Quizplus · Accepted Answer

T cells do not express CD40,and they do not respond directly to CD40 ligand.There is clear evidence that CD8⁺ cytolytic T lymphocyte (CTL)responses to viral infections require professional antigen-presenting cells (APCs)as well as CD4⁺ helper T cells.How this works is complicated;all viruses do not infect professional APCs,and helper T cells are class II MHC restricted whereas CD8⁺ CTL precursors are class I MHC restricted.Several mechanisms have been shown to contribute to naive CD8⁺ T cell activation in experimental systems.One mechanism is cross presentation of viral peptides by professional APCs that were not infected but acquired the viral antigens from other cells.Infected APCs may present viral peptides to CD4⁺ T cells,stimulating a helper T cell response,which then,via secreted cytokines,helps activate CD8⁺ T cells.Helper T cells may also enhance APC function of infected cells via CD40-CD40 ligand interactions.

Which of the Following Mechanisms Does NOT Contribute to the Generation