Trajectories of gene expression, seasonal influenza, and within-host seasonal immunity: transfer value to covid-19

As a novel approach we will combine trajectories or longitudinal studies of gene expression with information on annual influenza epidemics. Seasonality of gene expression in immune cells from blood could be a consequence of within-host seasonal immunity interacting with the seasonal pandemics of influenza (flu) in temperate regions and, thus, with potential valuable analogy transfer to the proposed seasonal development of covid-19. Here we operationalized within-host immunity as genes with both a significant seasonal term and a significant flu term in the sine-cosine model. Information on gene expression was based on microarray using RNase buffered blood samples collected randomly from a population-based cohort of Norwegian middle-aged women in 2003-2006, The Norwegian Women and Cancer (NOWAC) study. The unique discovery (N=425) and replication (N=432) design were based on identical sampling and preprocessing. Data on proportion of sick leaves due to flu, and the flu intensities per week was obtained from the National Institute of Public Health, giving a semi-ecological analysis. The discovery analysis found 2942 (48.1%) significant genes in a generalized seasonal model over four years. For 1051 within-host genes both the seasonal and the flu term were significant. These genes followed closely the flu intensities. The trajectories showed slightly more genes with a maximum in early winter than in late summer. Moving the flu intensity forward in time indicated a better fit 3-4 weeks before the observed influenza. In the replication analyses, 369 genes (35.1% of 1051) were significant. Exclusion of genes with unknown functions and with more than a season in difference reduced the number of genes in the discovery dataset to 305, illustrating the variability in the measurements and the problem in assessing weak biological relationships. Thus, we found for the first time a clear seasonality in gene expression with marked responses to the annual seasonal influenza in a unique discovery - replication design. Hypothetically, this could support the within-host seasonal immunity concept.