Antigen-specific CD8(+) T cells fail to respond to Shigella flexneri

Area of Science:

• Immunology
• Microbiology
• Cellular Biology

Background:

• CD8(+) T lymphocytes are key players in adaptive immunity against intracellular pathogens.
• Shigella flexneri, an enteric pathogen, secretes proteins into the host cytoplasm, a process typically leading to CD8(+) T cell activation.
• Despite this, CD8(+) T cells are not essential for protective immunity against Shigella.

Purpose of the Study:

• To investigate why CD8(+) T cells do not contribute to immunity against Shigella flexneri.
• To determine if CD8(+) T cells are primed during infection but fail to protect, or if priming is impaired.
• To assess Shigella's capacity to stimulate an antigen-specific CD8(+) T cell response.

Main Methods:

• Engineered a Shigella flexneri strain to constitutively secrete a viral CD8(+) T cell epitope using the type III secretion system.
• Characterized the CD8(+) T cell response to this engineered strain in mice and cultured cells.
• Assessed the impact of Shigella infection on T cell responses to cytoplasmically delivered antigens in antigen-presenting cells.

Main Results:

• No T cells specific for the viral epitope were stimulated in mice infected with the engineered Shigella strain.
• Epitope-specific T cells did not target cells infected with the recombinant Shigella strain.
• Shigella infection significantly reduced T cell responses to other antigens introduced into the cytoplasm of infected antigen-presenting cells.

Conclusions:

• Antigen-specific CD8(+) T cells are not primed during Shigella flexneri infection.
• This lack of priming results in limited host protection against Shigella during primary and subsequent infections.
• Shigella actively interferes with the mechanisms required for CD8(+) T cell activation.