Memory phenotype CD8+ T cells with innate function selectively develop in the absence of active Itk

Area of Science:

• Immunology
• Innate Immunity
• T cell biology

Background:

• CD8(+)CD44(hi) T cells exhibit memory-like phenotypes and innate immune functions, rapidly secreting IFN-gamma.
• These cells are crucial for innate responses to infections like Listeria monocytogenes.
• The regulatory signals governing these memory-like T cells remain largely unknown.

Purpose of the Study:

• To investigate the role of Tec kinase Itk in regulating CD8(+) T cells with innate immune function.
• To determine how Itk signaling impacts the development and phenotype of CD8(+)CD44(hi) T cells.

Main Methods:

• Analysis of CD8(+) T cell populations in wild-type and Itk-deficient (Itk null) mice.
• Assessment of T cell phenotype, including CD44 expression.
• Evaluation of IFN-gamma production upon stimulation with IL-12/IL-18.
• Functional assays using mouse infection models (Listeria monocytogenes) and lipopolysaccharide exposure.
• Cell transfer experiments into IFN-gamma null mice.

Main Results:

• A majority of CD8(+) T cells in Itk null mice display a CD44(hi) phenotype, resembling memory-like innate T cells.
• This phenotype is observed in mice with a kinase-dead Itk mutant, indicating active Itk signaling suppresses these cells.
• These CD8(+)CD44(hi) T cells in Itk null mice possess preformed IFN-gamma message and rapidly secrete IFN-gamma upon stimulation.
• Itk null mice exhibit enhanced responses to Listeria monocytogenes infection and lipopolysaccharide exposure due to increased IFN-gamma secretion.
• Transfer of these cells rescues the bacterial clearance capacity in IFN-gamma null mice infected with Listeria monocytogenes.

Conclusions:

• Active signaling through Tec kinases, specifically Itk, negatively regulates the development of memory-like CD8(+) T cells with innate immune functions.
• Itk kinase activity is crucial for controlling the expansion and maintenance of these innate effector T cells.
• Understanding Itk's role provides insights into the regulation of innate immunity and T cell memory.