Neurotropic viruses are a group of viruses that highly sensitive to central nervous system.As the first line of defense against pathogen invasion,the activation of pathogen recognition receptor signaling network in innate immune system plays a"double-edged"role in the process of neurotropic virus infection,which has both antiviral effect and may aggravate virus infection under certain circumstances.This article reviews the research progress on dual roles of pathogen recognition receptors in neurotropic virus infection.

Neurotropic viruses are a group of viruses that highly sensitive to central nervous system.As the first line of defense against pathogen invasion,the activation of pathogen recognition receptor signaling network in innate immune system plays a"double-edged"role in the process of neurotropic virus infection,which has both antiviral effect and may aggravate virus infection under certain circumstances.This article reviews the research progress on dual roles of pathogen recognition receptors in neurotropic virus infection.

At present,some studies have identified gain-of-function(GOF)mutations in phosphoinositide 3-kinase(PI3K)genes PIK3CD(which encodes p110δ)lead to activated PI3Kδ syndrome(APDS),which can cause immune deficiency,immune dis-order and even tumor by multiple mechanisms of internal immune system defects,such as reduction/senescence/depletion of T cells,impaired development of B cells,and reduced toxicity of NK cells.Here,we review clinical characteristics of APDS induced by PI3Kδ GOF and molecular mechanism of immune deficiency,focusing on molecular mechanism of lymphocyte development,differentiation and functional defects caused by GOF mutation.

Blood-brain barrier is a natural barrier between blood and brain tissue that can protect the brain from invasion by infectious pathogens in blood and maintain the homeostasis of the brain environment. However, neurotropic viruses can escape or disrupt blood-brain barrier and then invade the brain, causing serious complications in the central nervous system such as encephalitis and meningitis, which seriously threaten human life. This paper mainly summarized the research progress in the pathogenic mechanisms of common neurotropic viruses crossing blood-brain barrier and invading the central nervous system.

Exosomes are extracellular vesicles containing a variety of cell membrane molecules and related protein. They have been found to act as important intercellular messengers carrying functional RNAs, proteins and lipids that can induce phenotypic changes in recipient cells and promote cell activation or inhibition effect. In recent years, some studies have shown that exosomes can not only play an immune activation role to trigger antiviral immune response after viral infection, but also help to spread virus among cells, thus contributing to viral immune escape. Exosomes can either spread or limit an infection depending on the type of pathogen and the features of source cells, and can be studied as potential targets for development of antiviral drugs and vaccines. This review summarized the role of exosomes in viral infections with an emphasis on their potential contribution to pathogenesis.