Herpes Virus May Turn Brain’s Immune Cells Against Itself

WHO:

ScienceAlert - The study investigated herpes simplex virus type 1 (HSV-1) and microglia, specialized brain immune cells that monitor and maintain the brain by detecting threats, clearing dead cells and damaged tissue, and pruning neuronal connections.

Yahoo - The study investigated herpes simplex virus type 1 (HSV-1) and microglia, specialized brain immune cells that monitor and maintain the brain by detecting threats, clearing dead cells and damaged tissue, and pruning neuronal connections.

ScienceAlert - Neuroscientist Christy Niemeyer of the University of Colorado Anschutz said HSV-1 can put microglia into “emergency defense mode” and may compromise their everyday functions, including after the virus is gone.

Yahoo - Neuroscientist Christy Niemeyer of the University of Colorado Anschutz said HSV-1 can put microglia into “emergency defense mode” and may compromise their everyday functions, including after the virus is gone.

WHAT:

ScienceAlert - A study published in *PLOS Pathogens* found that HSV-1 can reprogram microglia, potentially helping explain how the virus contributes to inflammation associated with cognitive decline.

Yahoo - A study published in *PLOS Pathogens* found that HSV-1 can reprogram microglia, potentially helping explain how the virus contributes to inflammation associated with cognitive decline.

ScienceAlert - The proportion of interferon-responsive microglia was more than 30 times higher in HSV-1-infected mice than in mice given a mock treatment.

Yahoo - The proportion of interferon-responsive microglia was more than 30 times higher in HSV-1-infected mice than in mice given a mock treatment.

ScienceAlert - In affected cells, genes associated with normal brain maintenance, monitoring, and communication showed reduced expression. The researchers said this could impair microglial phagocytosis, reduce clearance of neurotoxic factors, and promote protein aggregation.

Yahoo - In affected cells, genes associated with normal brain maintenance, monitoring, and communication showed reduced expression. The researchers said this could impair microglial phagocytosis, reduce clearance of neurotoxic factors, and promote protein aggregation.

WHERE:

ScienceAlert - In the mouse experiment, HSV-1 was found in discrete spots in the brainstem, rather than throughout the brain; microglial activation markers were higher in virus-containing regions.

Yahoo - In the mouse experiment, HSV-1 was found in discrete spots in the brainstem, rather than throughout the brain; microglial activation markers were higher in virus-containing regions.

WHEN:

ScienceAlert - Researchers examined the mice’s brains six days after infecting them with HSV-1.

Yahoo - Researchers examined the mice’s brains six days after infecting them with HSV-1.

WHY:

ScienceAlert - Researchers said loss of microglia’s normal maintenance programs resembles changes reported in neurological disorders, including Alzheimer’s disease and multiple sclerosis; they proposed that viral infection may initiate similar microglial state changes.

Yahoo - Researchers said loss of microglia’s normal maintenance programs resembles changes reported in neurological disorders, including Alzheimer’s disease and multiple sclerosis; they proposed that viral infection may initiate similar microglial state changes.

HOW:

ScienceAlert - Researchers infected mice with HSV-1 and used genetic analysis and imaging to examine immune responses and map the virus’s location. Activated microglia showed increased interferon signaling, in which cells release proteins that act as warning signals to nearby cells.

Yahoo - Researchers infected mice with HSV-1 and used genetic analysis and imaging to examine immune responses and map the virus’s location. Activated microglia showed increased interferon signaling, in which cells release proteins that act as warning signals to nearby cells.

ScienceAlert - The researchers cautioned that the findings were demonstrated in a small number of mice, which were euthanized during the experiment; the study did not establish that they would develop neurodegeneration or that the same response occurs in humans.

Yahoo - The researchers cautioned that the findings were demonstrated in a small number of mice, which were euthanized during the experiment; the study did not establish that they would develop neurodegeneration or that the same response occurs in humans.

(UPDATED October 23, 2026 02:18 UTC)

A study in *PLOS Pathogens* found that herpes simplex virus type 1 can reprogram microglia, the brain’s immune cells, potentially helping explain how infection contributes to inflammation linked to cognitive decline. In mice, researchers found more than 30 times as many interferon-responsive microglia after infection as in animals given a mock treatment. Interferon proteins act as warning signals to nearby cells. The affected microglia showed reduced activity in genes involved in maintaining, monitoring, and communicating within the brain, which could weaken their ability to clear harmful material. The virus appeared in scattered areas of the brainstem, where signs of microglial activation were higher. Neuroscientist Christy Niemeyer said the virus may push these cells into emergency defense mode, potentially disrupting normal functions even after it is gone. The researchers cautioned that the findings came from a small mouse study and do not establish the same effects in people.