Helminth infection is associated with dampened cytokine responses to viral and bacterial stimulations in Tsimane forager-horticulturalists

Background

Soil-transmitted helminths (STHs) and humans share long co-evolutionary histories over which STHs have evolved strategies to permit their persistence by downregulating host immunity. Understanding the interactions between STHs and other pathogens can inform our understanding of human evolution and contemporary disease patterns.

Methodology

We worked with Tsimane forager-horticulturalists in the Bolivian Amazon, where STHs are prevalent. We tested whether STHs and eosinophil levels—likely indicative of infection in this population—are associated with dampened immune responses to in vitro stimulation with H1N1 and lipopolysaccharide (LPS) antigens. Whole blood samples (n = 179) were treated with H1N1 vaccine and LPS and assayed for 13 cytokines (INF-γ, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12p70, IL-13, GM-CSF and TNF-ɑ). We evaluated how STHs and eosinophil levels affected cytokine responses and T helper (Th) 1 and Th2-cytokine suite responses to stimulation.

Results

Infection with Ascaris lumbricoides was significantly (P ≤ 0.05) associated with lower response of some cytokines to H1N1 and LPS in women. Eosinophils were significantly negatively associated with some cytokine responses to H1N1 and LPS, with the strongest effects in women, and associated with a reduced Th1- and Th2-cytokine response to H1N1 and LPS in women and men.

Conclusions and implications

Consistent with the ‘old friends’ and hygiene hypotheses, we find that STHs were associated with dampened cytokine responses to certain viral and bacterial antigens. This suggests that STH infections may play an essential role in immune response regulation and that the lack of STH immune priming in industrialized populations may increase the risk of over-reactive immunity.

Lay Summary: Indicators of helminth infection were associated with dampened cytokine immune responses to in vitro stimulation with viral and bacterial antigens in Tsimane forager-horticulturalists in the Bolivian Amazon, consistent with the ‘old friends’ and hygiene hypotheses.

The Soil Bacterium Methylococcus capsulatus Bath Interacts with Human Dendritic Cells to Modulate Immune Function

The prevalence of inflammatory bowel disease (IBD) has increased in Western countries during the course of the twentieth century, and is evolving to be a global disease. Recently we showed that a bacterial meal of a non-commensal, non-pathogenic methanotrophic soil bacterium, Methylococcus capsulatus Bath prevents experimentally induced colitis in a murine model of IBD. The mechanism behind the effect has this far not been identified. Here, for the first time we show that M. capsulatus, a soil bacterium adheres specifically to human dendritic cells, influencing DC maturation, cytokine production, and subsequent T cell activation, proliferation and differentiation. We characterize the immune modulatory properties of M. capsulatus and compare its immunological properties to those of another Gram-negative gammaproteobacterium, the commensal Escherichia coli K12, and the immune modulatory Gram-positive probiotic bacterium, Lactobacillus rhamnosus GG in vitro. M. capsulatus induces intermediate phenotypic and functional DC maturation. In a mixed lymphocyte reaction M. capsulatus-primed monocyte-derived dendritic cells (MoDCs) enhance T cell expression of CD25, the γ-chain of the high affinity IL-2 receptor, supports cell proliferation, and induce a T cell cytokine profile different from both E. coli K12 and Lactobacillus rhamnosus GG. M. capsulatus Bath thus interacts specifically with MoDC, affecting MoDC maturation, cytokine profile, and subsequent MoDC directed T cell polarization.

Cardiovascular disease and type 2 diabetes in evolutionary perspective: a critical role for helminths?

Heart disease and type 2 diabetes are commonly believed to be rare among contemporary subsistence-level human populations, and by extension prehistoric populations. Although some caveats remain, evidence shows these diseases to be unusual among well-studied hunter-gatherers and other subsistence populations with minimal access to healthcare. Here we expand on a relatively new proposal for why these and other populations may not show major signs of these diseases. Chronic infections, especially helminths, may offer protection against heart disease and diabetes through direct and indirect pathways. As part of a strategy to insure their own survival and reproduction, helminths exert multiple cardio-protective effects on their host through their effects on immune function and blood lipid metabolism. Helminths consume blood lipids and glucose, alter lipid metabolism, and modulate immune function towards Th-2 polarization—which combined can lower blood cholesterol, reduce obesity, increase insulin sensitivity, decrease atheroma progression, and reduce likelihood of atherosclerotic plaque rupture. Traditional cardiometabolic risk factors, coupled with the mismatch between our evolved immune systems and modern, hygienic environments may interact in complex ways. In this review, we survey existing studies in the non-human animal and human literature, highlight unresolved questions and suggest future directions to explore the role of helminths in the etiology of cardio-metabolic disease.