Immunity without innate lymphoid cells

Antiviral Activities of Group I Innate Lymphoid Cells

Even before the adaptive immune response initiates, a potent group of innate antiviral cells responds to a wide range of viruses to limit replication and virus-induced pathology. Belonging to a broader family of recently discovered innate lymphoid cells (ILCs), antiviral group I ILCs are composed of conventional natural killer cells (cNK) and tissue-resident ILCs (ILC1s) that can be distinguished based on their location as well as by the expression of key cell surface markers and transcription factors. Functionally, blood-borne cNK cells recirculate throughout the body and are recruited into the tissue at sites of viral infection where they can recognize and lyse virus-infected cells. In contrast, ILC1s are poised in uninfected barrier tissues and respond not through lysis but with the production of antiviral cytokines. From their frontline tissue locations, ILC1s can even induce an antiviral state in uninfected tissue to preempt viral replication. Mounting evidence also suggests that ILC1s may have enhanced secondary responses to viral infection. In this review, we discuss recent findings demonstrating that ILC1s provide several critical layers of innate antiviral immunity and the mechanisms (when known) underlying protection.

Roles of Type 1, 2, and 3 Innate Lymphoid Cells in Herpes Simplex Virus 1 Infection In Vitro and In Vivo

Innate lymphoid cells (ILCs) play important roles in host defense and inflammation. They are classified into three distinct groups based on their cytokine and chemokine secretion patterns and transcriptome profiles. Here, we show that ILCs isolated from mice can be infected with herpes simplex virus 1 (HSV-1) but that subsequent replication of the virus is compromised. After infection, type 2 ILCs expressed significantly higher levels of granulocyte colony-stimulating factor (G-CSF), interleukin 1α (IL-1α), IL-6, IL-9, RANTES, tumor necrosis factor alpha (TNF-α), CXCL1, CXCL2, CXCL10, CCL3, and CCL4 than infected type 1 or type 3 ILCs. Transcriptome-sequencing (RNA-seq) analysis of the ILCs 24 h after HSV-1 infection revealed that 77 herpesvirus genes were detected in the infected type 3 ILCs, whereas only 11 herpesvirus genes were detected in infected type 1 ILCs and 27 in infected type 2 ILCs. Compared with uninfected cells, significant upregulation of over 4,000 genes was seen in the HSV-1-infected type 3 ILCs, whereas 414 were upregulated in the infected type 1 ILCs and 128 in the infected type 2 ILCs. In contrast, in all three cell types, only a limited number of genes were significantly downregulated. Type 1, type 2, and type 3 ILC-deficient mice were used to gain insights into the effects of the ILCs on the outcome of ocular HSV-1 infection. No significant differences were found on comparison with similarly infected wild-type mice or on comparison of the three strains of deficient mice in terms of virus replication in the eyes, levels of corneal scarring, latency-reactivation in the trigeminal ganglia, or T-cell exhaustion. Although there were no significant differences in the survival rates of infected ILC-deficient mice and wild-type mice, there was significantly reduced survival of the infected type 1 or type 3 ILC-deficient mice compared with type 2 ILC-deficient mice. Adoptive transfer of wild-type T cells did not alter survival or any other parameters tested in the infected mice. Our results indicate that type 1, 2, and 3 ILCs respond differently to HSV-1 infection in vitro and that the absence of type 1 or type 3, but not type 2, ILCs affects the survival of ocularly infected mice.IMPORTANCE In this study, we investigated for the first time what roles, if any, innate lymphoid cells (ILCs) play in HSV-1 infection. Analysis of isolated ILCs in vitro revealed that all three subtypes could be infected with HSV-1 but that they were resistant to replication. The expression profiles of HSV-1-induced cytokines/chemokines and cellular and viral genes differed among the infected type 1, 2, and 3 ILCs in vitro While ILCs play no role or a redundant role in the outcomes of latency-reactivation in infected mice, absence of type 1 and type 3, but not type 2, ILCs affects the survival of infected mice.

Innate Lymphoid Cells in Helminth Infections-Obligatory or Accessory?

ILCs burst onto the immunological scene with their involvement in bacterial and helminth infections. As their influence has emerged, it has become clear that they play a fundamental role in regulating barrier tissue homeostasis and the immune response during inflammation. A subset of ILCs, ILC2s, has become the focus of attention for many helminth biologists-stepping into the limelight as both the elusive initiator and amplifier of the type-2 response. In many of the early reports, conclusions as to their function were based on experiments using unadapted parasites or immune-compromised hosts. In this review we re-examine the generation and function of type-2 ILCs in helminth infection and the extent to which their roles may be essential or redundant, in both primary and challenge infections. ILC2s will be discussed in terms of a broader innate network, which when in dialogue with adaptive immunity, allows the generation of the anti-parasite response. Finally, we will review how helminths manipulate ILC2 populations to benefit their survival, as well as dampen systemic inflammation in the host, and how this understanding may be used to improve strategies to control disease.

Revisiting the Functional Impact of NK Cells

Immune responses are critical for the maintenance of homeostasis but can also upset the equilibrium, depending on the context and magnitude of the response. Natural killer (NK) cells are well known for their important roles in antiviral and antitumor immune responses, and they are currently used, mostly under optimized forms, as immunotherapeutic agents against cancer. Nevertheless, with accumulating examples of deleterious effects of NK cells, it is paramount to consider their negative contributions. Here, we critically review and comment on the literature surrounding undesirable aspects of NK cell activity, focusing on situations where they play a harmful rather than a protective role.