P.E.04.16 How the immune system faces seasonal threats

Introduction: Advances in Fluorescent-activated cytometry and sorting (FACS), and genotyping technology are helping to understand the contributions of gender, age and genetics to immune variation, but the impact of season on immune cells is largely unknown. Materials & Methods: FACS was used to examine many (101) immune cell populations, as described in Orru et al., Cell, 2013, in about 3,900 volunteers enrolled in SardiNIA Project. Subjects ranged in age from 18-103, and all lived in the Ogliastra region of Sardinia. Absolute cell counts were used for each population, and analysis of variation (ANOVA) was performed, considering subject age, sex and season of sampling as covariates. Results: While age was the major covariate on most traits, season was also found to have an important impact on several circulating cell populations, including monocytes and their subsets, myeloid Dendritic cells (mDCs), and Natural Killer T cells (NKT). The impact of season was notable in activated cells of these types, as measured by HLA class II expression or lack of L-selectin (CD62L). Discussion: As the activated cell types come from different hematopoietic lineages, they may demarcate a shared seasonal-activation mechanism. Our analyses also confirmed the significant seasonal influence on leukocytes, monocytes and lymphocytes described in the study of Castro-Dopico et al., Nat Comm 2015, and may give insight into the cell populations most involved in preparing for seasonal immune threats.