Herpes simplex encephalitis (HSE) is the most common sporadic viral encephalitis of childhood. Autosomal recessive (AR) UNC-93B and TLR3 deficiencies and autosomal dominant (AD) TLR3 and TRAF3 deficiencies underlie HSE in some children. We report here unrelated HSE children with AR or AD TRIF deficiency. The AR form of the disease was found to be due to a homozygous nonsense mutation that resulted in a complete absence of the TRIF protein. Both the TLR3- and the TRIF-dependent TLR4 signaling pathways were abolished. The AD form of disease was found to be due to a heterozygous missense mutation, resulting in a dysfunctional protein. In this form of the disease, the TLR3 signaling pathway was impaired, whereas the TRIF-dependent TLR4 pathway was unaffected. Both patients, however, showed reduced capacity to respond to stimulation of the DExD/H-box helicases pathway. To date, the TRIF-deficient patients with HSE described herein have suffered from no other infections. Moreover, as observed in patients with other genetic etiologies of HSE, clinical penetrance was found to be incomplete, as some HSV-1–infected TRIF-deficient relatives have not developed HSE. Our results provide what we believe to be the first description of human TRIF deficiency and a new genetic etiology for HSE. They suggest that the TRIF-dependent TLR4 and DExD/H-box helicase pathways are largely redundant in host defense. They further demonstrate the importance of TRIF for the TLR3-dependent production of antiviral IFNs in the CNS during primary infection with HSV-1 in childhood.

Identification of a chemokine analogue that antagonized CX3CL1-CX3CR1-dependent responses both in vitro and in vivo Chemokines are mainly involved in the recruitment of leukocytes into tissues, a key feature of inflammation. Through its unique receptor CX3CR1, the chemokine CX3CL1 participates in diverse inflammatory processes including arterial atherosclerosis and cerebral or renal inflammation. Using a phage display strategy, we engineered a hCX3CL1 analog (named F1) with a modified N terminus. F1 bound specifically to cells expressing hCX3CR1 and had a Kd value close to that of native CX3CL1. F1 was not a signaling molecule and did not induce chemotaxis, calcium flux, or CX3CR1 internalization. However, it potently inhibited the CX3CL1-induced calcium flux and chemotaxis in CX3CR1-expressing primary cells of human and murine origin with an IC50 of 5–50 nM. It also efficiently inhibited the cell adhesion mediated by the CX3CL1-CX3CR1 axis. Finally, in a noninfectious murine model of peritonitis, F1 strongly inhibited macrophage accumulation. These data reveal a prototype molecule that is the first bona fide antagonist of hCX3CR1. This molecule could be used as a lead compound for the development of a novel class of anti-inflammatory substances that act by inhibiting CX3CR1.