An immunological age index in bipolar disorder: A confirmatory factor analysis of putative immunosenescence markers and associations with clinical characteristics

Objectives The study aims to generate an immunological age (IA) trait on the basis of immune cell differentiation parameters, and to test whether the IA is related to age and disease characteristics. Methods Forty‐four euthymic type I bipolar disorder patients were included in this study. Five immunosenescence‐related parameters were assessed: proportions of late‐differentiated cells (e.g., CD3+CD8+CD28‐CD27‐ and CD3‐CD19+IgD‐CD27‐), and the expression of CD69, CD71, and CD152 after stimulation. Confirmatory factor analysis was applied to generate an IA trait underling the 5 measures. Results The best‐fit model was constituted by 4 parameters that were each related to an underlying IA trait, with 1 cell population positively correlated (CD3+CD8+CD28‐CD27‐ [λ = 0.544, where λ represents the loading of the parameter onto the IA trait] and 3 markers negatively correlated (CD69 [λ = −0.488], CD71 [λ = −0.833], and CD152 [λ = −0.674]). The IA trait was associated with chronological age (β = 0.360, p = .013) and the number of previous mood episodes (β = 0.426, p = .006). In a mediation model, 84% of the effect between manic episodes, and IA was mediated by body mass index. Conclusion In bipolar disorder type I, premature aging of the immune system could be reliably measured using an index that validated against chronological age, which was related to adverse metabolic effects of the disease course.