CD8 positive T-cells decrease neurogenesis and induce anxiety-like behaviour following hepatitis B vaccination.

Mounting evidence indicates the involvement of peripheral immunity in the regulation of brain function, influencing aspects such as neuronal development, emotion, and cognitive abilities. Previous studies from our laboratory have revealed that neonatal hepatitis B vaccination can downregulate hippocampal neurogenesis, synaptic plasticity and spatial learning memory. In the current post-epidemic era characterized by universal vaccination, understanding the impact of acquired immunity on neuronal function and neuropsychiatric disorders, along with exploring potential underlying mechanisms, becomes imperative. We employed hepatitis B vaccine-induced CD3 positive T cells in immunodeficient mice to investigate the key mechanisms through which T cell subsets modulate hippocampal neurogenesis and anxiety-like behaviours. Our data revealed that mice receiving hepatitis B vaccine-induced T cells exhibited heightened anxiety and decreased hippocampal cell proliferation compared to those receiving phosphate-buffered saline-T cells or wild-type mice. Importantly, these changes were predominantly mediated by infiltrated CD8⁺ T cells into the brain, rather than CD4⁺ T cells. Transcriptome profiling of CD8⁺ T cells unveiled that C-X-C motif chemokine receptor 6 positive (CXCR6⁺) CD8⁺ T cells were recruited into the brain through microglial and astrocyte-derived C-X-C motif chemokine ligand 16 (CXCL16). This recruitment process impaired neurogenesis and induced anxiety-like behaviour via tumour necrosis factor-α-dependent mechanisms. Our findings highlight the role of glial cell derived CXCL16 in mediating the recruitment of CXCR6⁺CD8⁺ T cell subsets into the brain. This mechanism represents a potential avenue for modulating hippocampal neurogenesis and emotion-related behaviours after hepatitis B vaccination.