The cornea is the anterior-most section of the eye, making this transparent protective outer layer continuously exposed to pathogens. The body’s response triggered by an infection could harm the cornea; therefore, the immune reaction must be specific and controlled. The cornea fights off infectious agents with immune cells that reside in it, such as macrophages and dendritic cells, and by recruiting effector T cells. The fate of these effector T cells had not been previously elucidated. It was unknown whether they continued to reside in the cornea and became responsible for immunological memory. Until recently, a shared idea was that tissue-resident memory T cells (TRM) are not present in the healthy cornea. However, researchers from the Peter Doherty Institute for Infection and Immunity have recently reported results that challenged this idea.
Corneal Tissue-Resident Memory T cells
The researchers used intravital 2-photon microscopy to examine T cell response in mice corneal cells infected with Herpes Simplex Virus (HSV). They reported that the recruitment of CD8+ T cells due to virus infections triggered the formation of TRM cells in the cornea. The ground-breaking aspect of the observations is that these motile corneal TRM cells kept surveillance of the cornea even after the viral infection had been resolved. Upon a secondary infection, TRM cells were able to promptly respond in situ, quickly recruit circulating memory T cells into the cornea, and eventually give rise to secondary TRM cells. Additionally, the researchers performed in vivo imaging of human eyes and reported the presence of highly motile patrolling cells in healthy corneas that looked very similar to the ones imaged in mice.
The conclusion reached from these observations is that TRM cells in the cornea provide a local protective immune response after pathogen exposure, providing further knowledge about how the eyes react against infections that may cause blindness, such as HSV. This study provides us with additional insight into the eye’s immune system and its response to infections, helping us understand conditions that may potentially be cured.
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