KLF12 Regulates Mouse NK Cell Proliferation.

NK cells are innate lymphocytes that play an integral role in tumor rejection and viral clearance. Unlike their other lymphocyte counterparts, NK cells have the unique ability to recognize and lyse target cells without prior exposure. However, there are no known NK cell-specific genes that are exclusively expressed by all NK cells. Therefore, identification of NK cell-specific genes would allow a better understanding of why NK cells are unique cytotoxic lymphocytes. From the Immunological Genome (ImmGen) Consortium studies, we identified kruppel-like factor 12 (Klf12), encoding a novel transcription factor, preferentially expressed in C57BL/6 mouse NK cells. KLF12 was dispensable for NK cell development, IFN-γ production, degranulation, and proliferation in Klf12 knockout mice. RNA-sequencing analysis revealed increased expression of Btg3, an antiproliferative gene, in KLF12-deficient NK cells compared with wild-type NK cells. Interestingly, competitive mixed bone marrow chimeric mice exhibited reduced development of KLF12-deficient NK cells, altered IFN-γ production and degranulation, and impairment of NK cell proliferation in vitro and in vivo in response to mouse CMV infection. KLF12-deficient NK cells from bone marrow chimeric mice also expressed higher levels of the IL-21R, which resulted in increased IL-21R signaling and correlated with greater inhibition of NK cell proliferation. Furthermore, IL-21 induced Btg3 expression, which correlated with arrested NK cell maturation and proliferation. In summary, we found that KLF12 regulates mouse NK cell proliferation potentially by regulating expression of Btg3 via IL-21.

NK cells in host responses to viral infections.

Natural killer (NK) cells are cytotoxic innate lymphocytes that play an important role in viral clearance. NK cell responses to viral infections were originally believed to be non-specific and lacked immune memory recall responses. It is now appreciated that NK cell responses to viral infections can be specific and in some cases memory recall responses are established. Increasing evidence also illuminates the complexity of NK cell interactions with both innate and adaptive immune cells. Here, we summarize the evidence for NK cell-specific memory responses to viral infections and the intricate reciprocal interactions between NK cells and other immune cells that dictate their activation and effector functions.

Unbiased modifier screen reveals that signal strength determines the regulatory role murine TLR9 plays in autoantibody production.

The autoimmune disease systemic lupus erythematosus has a complex environmental and multifactorial genetic basis. Genome-wide association studies have recently identified numerous disease-associated polymorphisms, but it remains unclear in which cells and during which step of pathogenesis specific polymorphisms interact to cause disease. Using a mouse model in which the same activating mutation (CD45E613R) causes distinct genetic background-dependent disease phenotypes, we performed a screen for genetic modifiers of autoreactivity between anti-nuclear Ab (ANA)-resistant CD45E613R.B6 and ANA-permissive CD45E613R.BALB/c mice. Within a novel autoreactivity-associated locus on chromosome 9, we identify a putative modifier, TLR9. Validating a role for TLR9 in modifying autoreactivity in the context of the CD45E613R mutation, manipulation of TLR9 gene dosage eliminates ANA in CD45E613R.BALB/c mice, but confoundingly permits ANA in CD45E613R.B6 mice. We demonstrate that sensitivity to ANA is modulated by strength of TLR9 signal, because stronger TLR9(B6) signals, but not weaker TLR9(BALB/c) signals, negatively regulate CD45E613R B cell development during competitive reconstitution at the central tolerance checkpoint. Our results identify a novel autoreactivity-associated locus and validate Tlr9 as a candidate gene within the locus. We further demonstrate a novel role for TLR9 signal strength in central tolerance, providing insight into the interplay of disease-associated polymorphisms at a discrete step of systemic lupus erythematosus pathogenesis.

Donor myocardial infarction impairs the therapeutic potential of bone marrow cells by an interleukin-1-mediated inflammatory response.

Delivery of bone marrow cells (BMCs) to the heart has substantially improved cardiac function in most rodent models of myocardial infarction (MI), but clinical trials of BMC therapy have led to only modest improvements. Rodent models typically involve intramyocardial injection of BMCs from distinct donor individuals who are healthy. In contrast, autologous BMCs from individuals after MI are used for clinical trials. Using BMCs from donor mice after MI, we discovered that recent MI impaired BMC therapeutic efficacy. MI led to myocardial inflammation and an increased inflammatory state in the bone marrow, changing the BMC composition and reducing their efficacy. Injection of a general anti-inflammatory drug or a specific interleukin-1 inhibitor to donor mice after MI prevented this impairment. Our findings offer an explanation of why human trials have not matched the success of rodent experiments and suggest potential strategies to improve the success of clinical autologous BMC therapy.

Differential impact of the CD45 juxtamembrane wedge on central and peripheral T cell receptor responses.

The cooperative activity of protein tyrosine kinases and phosphatases plays a central role in regulation of T cell receptor (TCR) signal strength. Perturbing this balance, and thus the threshold for TCR signals, has profound impacts on T cell development and function. We previously generated mice containing a point mutation in the juxtamembrane wedge of the receptor-like protein tyrosine phosphatase CD45. Demonstrating the critical negative regulatory function of the wedge, the CD45 E613R (WEDGE) mutation led to a lymphoproliferative disorder (LPD) and a lupus-like autoimmune syndrome. Using genetic, cellular, and biochemical approaches, we now demonstrate that the CD45 wedge influences T cell development and function. Consistent with increased TCR signal strength, WEDGE mice have augmented positive selection and enhanced sensitivity to the CD4-mediated disease experimental autoimmune encephalitis (EAE). These correspond with hyperresponsive calcium and pERK responses to TCR stimulation in thymocytes, but surprisingly, not in peripheral T cells, where these responses are actually depressed. Together, the data support a role for the CD45 wedge in regulation of T cell responses in vivo and suggest that its effects depend on cellular context.