STAT6 Deletion Converts the Th2 Inflammatory Pathology Afflicting LatY136F Mice into a Lymphoproliferative Disorder Involving Th1 and CD8 Effector T Cells

Abstract

Mutant mice in which tyrosine 136 of linker for activation of T cells (LAT) was replaced with a phenylalanine (LatY136F mice) develop a lymphoproliferative disorder involving polyclonal CD4 effector T cells that produce massive amounts of IL-4 and trigger severe Th2 inflammation. Naive CD4 T cells can themselves produce IL-4 and thereby initiate a self-reinforcing positive regulatory loop that involves the STAT6 transcription factor and leads to Th2 polarization. We determined the functional outcome that results when LatY136F T cells differentiate in the absence of such STAT6-dependent regulatory loop. The lack of STAT6 had no effect on the timing and magnitude of the lymphoproliferative disorder. However, in LatY136F mice deprived of STAT6, the expanding CD4 T cell population was dominated by Th1 effector cells that triggered B cell proliferation, elevated IgG2a and IgG2b levels as well as the production of autoantibodies. In contrast to LatY136F mice that showed no CD8 T cell expansion, the CD8 T cells present in LatY136F mice deprived of STAT6 massively expanded and acquired effector potential. Therefore, the lack of STAT6 is sufficient to convert the Th2 lymphoproliferative disorder that characterizes LatY136F mice into a lymphoproliferative disorder that is dominated by Th1 and CD8 effector T cells. The possibility to dispose of a pair of mice that differs by a single gene and develops in the absence of deliberate immunization large numbers of Th cells with almost reciprocal polarization should facilitate the identification of genes involved in the control of normal and pathological Th cell differentiation.

The Importance of LAT in the Activation, Homeostasis, and Regulatory Function of T Cells

“…This phenotype is very similar to the one seen in LATY136F knock-in mice, in which the LAT-PLC-␥1 interaction is abolished (16,17). Data from our laboratory (39) and others (40) have demonstrated that this disease arises independently of abnormal thymic selection in the knock-in mice. Instead, the LATY136F mutation in peripheral T cells is sufficient to confer pathogenicity and induce a similar disease.…”

Loss of the LAT Adaptor Converts Antigen-Responsive T Cells into Pathogenic Effectors that Function Independently of the T Cell Receptor

“…In the course of activation, Lat D/Y136F and Lat D/À CD4 + T cells underwent a conversion into a state where they express dramatically reduced amounts of TCR at their surface and became refractory to TCR engagement. Dramatically reduced amounts of TCR are also present at the surface of gd and CD8 + T cells that express mutated forms of LAT and give rise to lymphoproliferative disorders (Archambaud et al, 2009;Nunez-Cruz et al, 2003). Because the TCR lo phenotype of Lat Y136F/Y136F CD4 + T cells can not be reversed by preventing TCR-MHCII interactions (Wang et al, 2008), such stringent TCR dowregulation likely results from intrinsic constitutive signals triggered by the presence of defective LAT signalosomes.…”

“…Cytokine Measurement IL-4 and IL-2 production was measured as previously described (Archambaud et al, 2009). For IFN-g production, CD4 + T cells were stimulated for 48 hr with graded concentrations of CD3 antibodies in the presence of a fixed concentration (0.5 mg/ml) of CD28 antibody.…”

LAT signaling pathology: an “autoimmune” condition without T cell self-reactivity

“…Six weeks after transfer, the expanding Lat Y136F CD4 + T cell reached a plateau that corresponds to approximately 80 x 10 6 cells per spleen [10]. Interestingly, upon sequential adoptive transfer into Cd3e D5/D5 hosts, Lat Y136F CD4 + T cells keep their effector function but show a gradual loss of their replicative capacity [19]. This observation is reminiscent of the replicative exhaustion that occurs in effector T cells during persistent antigen stimulation, suggesting that expanding Lat Y136F CD4 + T cells reach replicative senescence, accounting for the lack of malignant degeneration of the Lat Y136F lymphoproliferative disorder.…”

“…It has been suggested that upon TCR engagement, the few T cells that colonize the periphery of Lat Y136F and Lat Y7/8/9F newborn mice can produce IL-4, thereby initiating a self-reinforcing positive regulatory loop involving the transcription factor STAT-6 and leading to Th2 polarization. The functional outcome when Lat Y136F CD4 + T cells differentiate in the absence of STAT-6 was analyzed and the lack of STAT-6 had no effect on the timing and magnitude of the lymphoproliferative disorder [19]. However, the lymphoproliferative disorder was dominated by Th1 effector cells that produced high levels of IFN-g, triggered B cell proliferation, and elevated IgG2a and IgG2b and the production of autoantibodies.…”