HLA-DRB1*15:01 drives sex- and age-dependent microglial immune phenotypes and neuroimmune signaling

The major histocompatibility complex class II (MHC-II) pathway is central to adaptive immunity and immune tolerance, and its age-related dysregulation is increasingly linked to chronic neuroinflammation. The HLA-DRB1*15:01 allele, the strongest genetic risk factor for multiple sclerosis, has been implicated in shaping pathogenic CD4⁺ T-cell responses and broader neuroimmune vulnerability, yet how this allele modulates age- and sex-dependent neuroimmune processes within the central nervous system (CNS) remains poorly defined.

We investigated the impact of HLA-DRB1*15:01 expression using a humanized mouse model (HLA mice) and wild-type (WT) controls. Male and female mice were analyzed at 6, 9, and 15 months of age, with endocrine stratification in females. Behavioral testing, flow cytometry, immunofluorescence, and multiplex cytokine analyses were used to assess cognitive performance, glial immune-associated changes and oxidative stress, astrocyte-microglia IL-3/IL-3R signaling, endothelial activation, selective immune cell accumulation at CNS borders, tissue organization, and hippocampal cytokine profiles.

HLA mice developed age- and sex-dependent cognitive impairment, most pronounced in aged females. HLA-DRB1*15:01 expression promoted progressive microglial immune-associated changes, characterized by increased CD14 and CD68 expression, elevated mitochondrial oxidative stress, altered astrocyte phenotypes, and enhanced IL-3/IL-3R signaling. Hippocampal axonal and myelin organization was disrupted in aged HLA mice and was spatially associated with increased microglial presence. HLA mice also exhibited selective immune remodeling, including increased accumulation of CD4⁺ T cells and NK1.1⁺CD3⁺ natural killer T (NKT) cells, particularly in females, accompanied by endothelial activation marked by elevated ICAM-1 and E-selectin expression. Hippocampal cytokine profiling revealed selective sex-biased alterations, without broad induction of classical inflammatory cytokines.

Together, these findings demonstrate that HLA-DRB1*15:01 drives a coordinated, age- and sex-dependent neuroinflammatory program linking behavioral dysfunction, glial immune-associated changes and oxidative stress, selective immune cell recruitment, endothelial activation, tissue remodeling, and targeted cytokine imbalance. This integrated phenotype provides mechanistic insight into how this major MS risk allele confers vulnerability to chronic neuroinflammation during aging, with heightened impact in females, independent of reproductive cycling stage.