Slc43a2^(+)T cell metastasis from spleen to brain in RGNNV infected teleost

The origin of T cells in the teleost's brain is unclear.While viewing the central nervous system(CNS)as immune privileged has been widely accepted,previous studies suggest that T cells residing in the thymus but not in the spleen of the teleost play an essential role in communicating with the peripheral organs.Here,we identified nine T cell subpopulations in the thymus and spleen of orange-spotted grouper(Epinephelus coioices)through single-cell RNA-sequencing analysis.After viral CNS infection with red-spotted grouper nervous necrosis virus(RGNNV),the number of slc43a2^(+)T cells synchronously increased in the spleen and brain.During the infection tests in asplenic zebrafish(tlx1^▲zebrafish model),no increase in the number of slc43a2^(+)T cells was observed in the brain.Single-cell transcriptomic analysis indicated that slc43a2^(+)T cells mature and functionally differentiate within the spleen and then migrate into the brain to trigger an immune response.This study suggests a novel route for T cell migration from the spleen to the brain during viral infection in fish.