Functional analysis of acquired CD28 mutations identified in cutaneous T cell lymphoma.

CD28 is the major costimulatory receptor on T cells regulating proliferation, survival and effector function. Acquired mutations in the extracellular domain of CD28 have been identified in patients with cutaneous T cell lymphoma, angioimmunoblastic T cell lymphoma and other T cell neoplasms, suggesting it may contribute to disease pathogenesis. We used a heterologous system in which mutant human CD28 was expressed on primary murine T cells deficient in CD28 to ascertain how specific mutations identified in a genetic screen of patients with cutaneous T cell lymphoma affected normal T cell function. All three mutant CD28 proteins examined enhanced CD28-dependent T cell proliferation and effector function. These data suggest that the mutant CD28 isoforms could accelerate tumor cell growth and increase tumor burden in affected patients. Interruption of CD28:ligand interactions may be an effective, targeted therapy for a subset of patients whose tumors bear the mutant CD28 receptor.

Haploinsufficiency of NADPH Oxidase Subunit Neutrophil Cytosolic Factor 2 Is Sufficient to Accelerate Full-Blown Lupus in NZM 2328 Mice.

OBJECTIVE: We have previously established that the gene for neutrophil cytosolic factor 2 (NCF-2) predisposes to lupus, and we have identified lupus patients with point mutations that are predicted to cause reduced NADPH oxidase activity. We undertook this study to investigate the relationship between reduced leukocyte NADPH oxidase activity and immune dysregulation associated with systemic lupus erythematosus (SLE). METHODS: We generated NCF-2-null mice, in which NADPH oxidase activity is absent, on the nonautoimmune C57BL/6 (B6) mouse background and on the NZM 2328 mouse background, a polygenic model in which mice spontaneously develop lupus. Clinical disease, serology, and immunopathology were evaluated. RESULTS: NCF-2-null mice on the B6 background were susceptible to Aspergillus fumigatus pneumonia characteristic of chronic granulomatous disease, but did not develop systemic lupus disease. In contrast, NCF-2-null and even NCF-2-haploinsufficient mice on the NZM 2328 background developed accelerated full-blown lupus with significantly accelerated lupus kidney disease. This was characterized by more rapid development of hyperactive B cell and T cell immune compartments, increased expression of type I interferon-responsive genes, and generation of neutrophil extracellular traps, which were observed even in the absence of NADPH oxidase activity. CONCLUSION: Just as patients with chronic granulomatous disease who lack NADPH oxidase rarely develop SLE, NCF-2-null mice on a nonautoimmune background were susceptible to a chronic granulomatous disease-like opportunistic infection but did not develop lupus. In contrast, on a lupus-prone background, even haploinsufficiency of NCF-2 accelerated the development of full-blown lupus disease. This establishes an interaction between reduced oxidase activity and other lupus-predisposing genes, paralleling human SLE-associated variants predicted to have only reduced NADPH oxidase activity.

Continuous engagement of a self-specific activation receptor induces NK cell tolerance.

Natural killer (NK) cell tolerance mechanisms are incompletely understood. One possibility is that they possess self-specific activation receptors that result in hyporesponsiveness unless modulated by self-major histocompatability complex (MHC)-specific inhibitory receptors. As putative self-specific activation receptors have not been well characterized, we studied a transgenic C57BL/6 mouse that ubiquitously expresses m157 (m157-Tg), which is the murine cytomegalovirus (MCMV)-encoded ligand for the Ly49H NK cell activation receptor. The transgenic mice were more susceptible to MCMV infection and were unable to reject m157-Tg bone marrow, suggesting defects in Ly49H(+) NK cells. There was a reversible hyporesponsiveness of Ly49H(+) NK cells that extended to Ly49H-independent stimuli. Continuous Ly49H-m157 interaction was necessary for the functional defects. Interestingly, functional defects occurred when mature wild-type NK cells were adoptively transferred to m157-Tg mice, suggesting that mature NK cells may acquire hyporesponsiveness. Importantly, NK cell tolerance caused by Ly49H-m157 interaction was similar in NK cells regardless of expression of Ly49C, an inhibitory receptor specific for a self-MHC allele in C57BL/6 mice. Thus, engagement of self-specific activation receptors in vivo induces an NK cell tolerance effect that is not affected by self-MHC-specific inhibitory receptors.

TLR9-dependent recognition of MCMV by IPC and DC generates coordinated cytokine responses that activate antiviral NK cell function.

Natural interferon-producing cells (IPC) respond to viruses by secreting type I interferon (IFN) and interleukin-12 (IL-12). Toll-like receptor (TLR) 9 mediates IPC recognition of some of these viruses in vitro. However, whether TLR9-induced activation of IPC is necessary for an effective antiviral response in vivo is not clear. Here, we demonstrate that IPC and dendritic cells (DC) recognize murine cytomegalovirus (MCMV) through TLR9. TLR9-mediated cytokine secretion promotes viral clearance by NK cells that express the MCMV-specific receptor Ly49H. Although depletion of IPC leads to a drastic reduction of the IFN-alpha response, this allows other cell types to secrete IL-12, ensuring normal IFN-gamma and NK cell responses to MCMV. We conclude that the TLR9/MyD88 pathway mediates antiviral cytokine responses by IPC, DC, and possibly other cell types, which are coordinated to promote effective NK cell function and MCMV clearance.

Coordinate expression of cytokines and chemokines by NK cells during murine cytomegalovirus infection.

Cytokines and chemokines activate and direct effector cells during infection. We previously identified a functional group of five cytokines and chemokines, namely, IFN-gamma, activation-induced T cell-derived and chemokine-related cytokine/lymphotactin, macrophage-inflammatory protein 1alpha, macrophage-inflammatory protein 1beta, and RANTES, coexpressed in individual activated NK cells, CD8(+) T cells, and CD4(+) Th1 cells in vitro and during in vivo infections. However, the stimuli during infection were not known. In murine CMV (MCMV) infection, the DAP12/KARAP-associated Ly49H NK cell activation receptor is crucial for resistance through recognition of MCMV-encoded m157 but NK cells also undergo in vivo nonspecific responses to uncharacterized stimuli. In this study, we show that Ly49H ligation by m157 resulted in a coordinated release of all five cytokines/chemokines from Ly49H(+) NK cells. Whereas other cytokines also triggered the release of these cytokines/chemokines, stimulation was not confined to the Ly49H(+) population. At the single-cell level, the production of the five mediators showed strong positive correlation with each other. Interestingly, NK cells were a major source of these five cytokines/chemokines in vitro and in vivo, whereas infected macrophages produced only limited amounts of macrophage-inflammatory protein 1alpha, macrophage-inflammatory protein1beta, and RANTES. These findings suggest that both virus-specific and nonspecific NK cells play crucial roles in activating and directing other inflammatory cells during MCMV infection.