Racial Disparities in Plasma Cytokine and Microbiome Profiles

Many health issues prevalent in African American (AA) populations are associated with chronic inflammation and related health conditions, including autoimmune diseases, infectious diseases, neurologic disorders, metabolic syndromes, and others. The current study aims to understand plasma microbiome translocation as a potential trigger for chronic inflammation.

In this study, 16 Caucasian American (CA) and 22 African American (AA) healthy individuals were recruited. Microbial DNA was isolated from the plasma samples and sequenced via microbial 16S rRNA V3-4 sequencing. The plasma levels of 33 cytokines and chemokines were evaluated. The proinflammatory microbiomes were verified using human THP-1 cells in vitro.

The plasma levels of IL-6, IL-15, MIP-1α, MIP-1β, and MIP-3α were higher in the AA people, whereas IL-1α and IL-27 were elevated in the CA people. The plasma microbiomes exhibited eight bacterial genera/phyla differentially enriched in the CA and AA people. Given the critical role of IL-6 in chronic inflammation and associated diseases, we identified five bacteria genera significantly associated with IL-6. The abundance of Actinomyces was positively correlated with the plasma IL-6 level (r = 0.41, p = 0.01), while the abundance of Kurthia (r = -0.34, p = 0.04), Noviherbaspirillum (r = -0.34, p = 0.04), Candidatus Protochlamydia (r = -0.36, p = 0.03), and Reyranella (r = -0.39, p = 0.02) was negatively correlated with this. Finally, the THP-1 cells treated with heat-killed bacteria produced higher levels of IL-6 in vitro in response to the Actinomyces species compared to the species in the genus either uncorrelated or negatively correlated with IL-6.

This is the first study to report potential blood microbiome translocation as a driver for persistently elevated IL-6 levels in the periphery in healthy AA versus CA people. Understanding the plasma microbiome linked to the IL-6 levels in people with different racial backgrounds is essential to unraveling the therapeutic approaches to improve precision medicine.