No abstract

We describe a homozygous copy number variant that disrupts the function of Dock2 in a commercially available C57BL/6 mouse strain that is widely used for backcrossing. This Dock2 allele was presumed to have spontaneously arisen in a colony of Irf5 knockout mice. We discovered that this allele has been inadvertently backcrossed into multiple mutant mouse lines, including two lines engineered to be deficient in Siae and Cmah. This particular subline of C57BL/6 mice also exhibits several striking immune phenotypes that have been previously described in the context of Dock2 deficiency. Inadvertent backcrossing of a number of gene-targeted mice into this background has complicated the interpretation of several immunological studies. In light of these findings, published studies involving immune or hematopoietic phenotypes where these mice have been used as controls, as experimental animals, or for backcrossing will need to be reinterpreted.

Although NF-κB1 p50/p105 has critical roles in immunity, the mechanism by which NF-κB1 regulates inflammatory responses is unclear. In this study, we analyzed the gene expression profile of LPS-stimulated Nfkb1−/− macrophages that lack both p50 and p105. Deficiency of p50/p105 selectively increased the expression of IFN-responsive genes, which correlated with increased IFN-β expression and STAT1 phosphorylation. IFN Ab-blocking experiments indicated that increased STAT1 phosphorylation and expression of IFN-responsive genes observed in the absence of p50/p105 depended upon autocrine IFN-β production. Markedly higher serum levels of IFN-β were observed in Nfkb1−/− mice than in wild-type mice following LPS injection, demonstrating that Nfkb1 inhibits IFN-β production under physiological conditions. TPL-2, a mitogen-activated protein kinase kinase kinase stabilized by association with the C-terminal ankyrin repeat domain of p105, negatively regulates LPS-induced IFN-β production by macrophages via activation of ERK MAPK. Retroviral expression of TPL-2 in Nfkb1−/− macrophages, which are deficient in endogenous TPL-2, reduced LPS-induced IFN-β secretion. Expression of the C-terminal ankyrin repeat domain of p105 in Nfkb1−/− macrophages, which rescued LPS activation of ERK, also inhibited IFN-β expression. These data indicate that p50/p105 negatively regulates LPS-induced IFN signaling in macrophages by stabilizing TPL-2, thereby facilitating activation of ERK.

The control of cytoskeletal dynamics by dedicator of cytokinesis 2 (DOCK2), a hematopoietic cell-specific actin effector protein, has been implicated in TCR signaling and T cell migration. Biallelic mutations in Dock2 have been identified in patients with a recessive form of combined immunodeficiency with defects in T, B, and NK cell activation. Surprisingly, we show in this study that certain immune functions of CD8 + T cells are enhanced in the absence of DOCK2. Dock2-deficient mice have a pronounced expansion of their memory T cell compartment. Bone marrow chimera and adoptive transfer studies indicate that these memory T cells develop in a cell-intrinsic manner following thymic egress. Transcriptional profiling, TCR repertoire analyses, and cell surface marker expression indicate that Dock2-deficient naive CD8 + T cells directly convert into virtual memory cells without clonal effector T cell expansion. This direct conversion to memory is associated with a selective increase in TCR sensitivity to self-peptide MHC in vivo and an enhanced response to weak agonist peptides ex vivo. In contrast, the response to strong agonist peptides remains unaltered in Dock2-deficient T cells. Collectively, these findings suggest that the regulation of the actin dynamics by DOCK2 enhances the threshold for entry into the virtual memory compartment by negatively regulating tonic TCR triggering in response to weak agonists.