Evolution, the Immune System, and the Health Consequences of Socioeconomic Inequality

Life-course socioeconomic position and the gut microbiome in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL)

Socioeconomic position (SEP) in childhood and beyond may influence the gut microbiome, with implications for disease risk. Studies evaluating the relationship between life-course SEP and the gut microbiome are sparse, particularly among Hispanic/Latino individuals, who have a high prevalence of low SEP. We use the Hispanic Community Health Study/Study of Latinos (HCHS/SOL), a population-based cohort study conducted in four field centers in the United States (U.S.), to evaluate the association between life-course SEP and gut microbiome composition. Life-course SEP indicators included parental education (proxy of childhood SEP), current SEP (n = 2174), and childhood (n = 988) and current economic hardship (n = 994). Shotgun sequencing was performed on stool samples. Analysis of Compositions of Microbiomes was used to identify associations of life-course SEP indicators with gut microbiome species and functions. Parental education and current SEP were associated with the overall gut microbiome composition; however, parental education and current education explained more the gut microbiome variance than the current SEP. A lower parental education and current SEP were associated with a lower abundance of species from genus Bacteroides. In stratified analysis by nativity, we found similar findings mainly among foreign-born participants. Early-life SEP may have long-term effects on gut microbiome composition underscoring another biological mechanism linking early childhood factors to adult disease.

Effects of Climate Change on the Immune System: A Narrative Review

Background and Aims

Human activities have greatly influenced global temperatures, leading to climate change and global warming. This narrative review aims to explore the relationship between climate change and the immune system, focusing on how environmental stressors can affect immune regulation, leading to both hyperactivity and suppression.

Methods

A comprehensive search was conducted in PubMed and Google Scholar for peer-reviewed studies published up to June 2024. The search terms included "climate change," "human health," "infection," "immunity," and "disease." Inclusion criteria were based on relevance, originality, and accessibility.

Results

Exposure to elevated temperatures can significantly impair immune system cells, leading to an overproduction of signaling molecules that promote inflammation. Temperature fluctuations have been shown to influence various aspects of the adaptive immune response, including immune cell mobilization, antigen processing and presentation, lymphocyte trafficking and activation, and the functionality of B and T cells. Notably, some research suggests that heat stress negatively impacts B lymphocyte differentiation, replication, and proportion, resulting in decreased immunoglobulin and cytokine production, and contributing to immunosuppression. Additionally, climate change-related exposures can compromise epithelial barriers in the skin, lungs, and gut, leading to microbial dysbiosis, and immune dysregulation. Furthermore, environmental factors such as temperature variations, humidity, and air pollutant levels may exacerbate the prevalence of infectious diseases, including measles and HIV, with varying impacts on acute, chronic, and latent infections, further contributing to immune variability.

Conclusion

Climate change, particularly increased temperatures, significantly impacts immune system function, leading to both heightened inflammatory responses, and immunosuppression. Future research should focus on developing comprehensive and sustainable management strategies to enhance health resilience in the face of ongoing climatic changes.

Protective effects of Mycobacterium vaccae ATCC 15483 against "Western"-style diet-induced weight gain and visceral adiposity in adolescent male mice

The prevalence of noncommunicable inflammatory disease is increasing in modern urban societies, posing significant challenges to public health. Novel prevention and therapeutic strategies are needed to effectively deal with this issue. One promising approach is leveraging microorganisms such as Mycobacterium vaccae ATCC 15483, known for its anti-inflammatory, immunoregulatory, and stress-resilience properties. This study aimed to assess whether weekly subcutaneous administrations of a whole-cell, heat-killed preparation of M. vaccae ATCC 15483 (eleven injections initiated one week before the onset of the diet intervention), relative to vehicle injections, in adolescent male C57BL/6N mice can mitigate inflammation associated with Western-style diet-induced obesity, which is considered a risk factor for a number of metabolic and inflammatory diseases. Our results show that treatment with M. vaccae ATCC 15483 prevented Western-style diet-induced excessive weight gain, visceral adipose tissue accumulation, and elevated plasma leptin concentrations. The Western-style diet, relative to a control diet condition, decreased alpha diversity and altered the community composition of the gut microbiome, increasing the Bacillota to Bacteroidota ratio (formerly referred to as the Firmicutes to Bacteroidetes ratio). Despite the finding that M. vaccae ATCC 15483 prevented Western-style diet-induced excessive weight gain, visceral adipose tissue accumulation, and elevated plasma leptin concentrations, it had no effect on the diversity or community composition of the gut microbiome, suggesting that it acts downstream of the gut microbiome to alter immunometabolic signaling. M. vaccae ATCC 15483 reduced baseline levels of biomarkers of hippocampal neuroinflammation and microglial priming, such as Nfkbia and Nlrp3, and notably decreased anxiety-like defensive behavioral responses. The current findings provide compelling evidence supporting the potential for M. vaccae ATCC 15483 as a promising intervention for prevention or treatment of adverse immunometabolic outcomes linked to the consumption of a Western-style diet and the associated dysbiosis of the gut microbiome.

Advancing microbiome research in Māori populations: insights from recent literature exploring the gut microbiomes of underrepresented and Indigenous peoples

The gut microbiome plays vital roles in human health, including mediating metabolism, immunity, and the gut-brain axis. Many ethnicities remain underrepresented in gut microbiome research, with significant variation between Indigenous and non-Indigenous peoples due to dietary, socioeconomic, health, and urbanization differences. Although research regarding the microbiomes of Indigenous peoples is increasing, Māori microbiome literature is lacking despite widespread inequities that Māori populations face. These inequities likely contribute to gut microbiome differences that exacerbate negative health outcomes. Characterizing the gut microbiomes of underrepresented populations is necessary to inform efforts to address health inequities. However, for microbiome research to be culturally responsible and meaningful, study design must improve to better protect the rights and interests of Indigenous peoples. Here, we discuss barriers to Indigenous participation in research and the role disparities may play in shaping the gut microbiomes of Indigenous peoples, with a particular focus on implications for Māori and areas for improvement.

Evolution and the critical role of the microbiota in the reduced mental and physical health associated with low socioeconomic status (SES)

The evolution of the gut-microbiota-brain axis in animals reveals that microbial inputs influence metabolism, the regulation of inflammation and the development of organs, including the brain. Inflammatory, neurodegenerative and psychiatric disorders are more prevalent in people of low socioeconomic status (SES). Many aspects of low SES reduce exposure to the microbial inputs on which we are in a state of evolved dependence, whereas the lifestyle of wealthy citizens maintains these exposures. This partially explains the health deficit of low SES, so focussing on our evolutionary history and on environmental and lifestyle factors that distort microbial exposures might help to mitigate that deficit. But the human microbiota is complex and we have poor understanding of its functions at the microbial and mechanistic levels, and in the brain. Perhaps its composition is more flexible than the microbiota of animals that have restricted habitats and less diverse diets? These uncertainties are discussed in relation to the encouraging but frustrating results of attempts to treat psychiatric disorders by modulating the microbiota.

Food desert residence has limited impact on veteran fecal microbiome composition: a U.S. Veteran Microbiome Project study

IMPORTANCE

Social and economic inequities can have a profound impact on human health. The inequities could result in alterations to the gut microbiome, an important factor that may have profound abilities to alter health outcomes. Moreover, the strong correlations between social and economic inequities have been long understood. However, to date, limited research regarding the microbiome and mental health within the context of socioeconomic inequities exists. One particular inequity that may influence both mental health and the gut microbiome is living in a food desert. Persons living in food deserts may lack access to sufficient and/or nutritious food and often experience other inequities, such as increased exposure to air pollution and poor access to healthcare. Together, these factors may confer a unique risk for microbial perturbation. Indeed, external factors beyond a food desert might compound over time to have a lasting effect on an individual's gut microbiome. Therefore, adoption of a life-course approach is expected to increase the ecological validity of research related to social inequities, the gut microbiome, and physical and mental health.

The old friends hypothesis: evolution, immunoregulation and essential microbial inputs

In wealthy urbanised societies there have been striking increases in chronic inflammatory disorders such as allergies, autoimmunity and inflammatory bowel diseases. There has also been an increase in the prevalence of individuals with systemically raised levels of inflammatory biomarkers correlating with increased risk of metabolic, cardiovascular and psychiatric problems. These changing disease patterns indicate a broad failure of the mechanisms that should stop the immune system from attacking harmless allergens, components of self or gut contents, and that should terminate inappropriate inflammation. The Old Friends Hypothesis postulates that this broad failure of immunoregulation is due to inadequate exposures to the microorganisms that drive development of the immune system, and drive the expansion of components such as regulatory T cells (Treg) that mediate immunoregulatory mechanisms. An evolutionary approach helps us to identify the organisms on which we are in a state of evolved dependence for this function (Old Friends). The bottom line is that most of the organisms that drive the regulatory arm of the immune system come from our mothers and family and from the natural environment (including animals) and many of these organisms are symbiotic components of a healthy microbiota. Lifestyle changes that are interrupting our exposure to these organisms can now be identified, and many are closely associated with low socioeconomic status (SES) in wealthy countries. These insights will facilitate the development of education, diets and urban planning that can correct the immunoregulatory deficit, while simultaneously reducing other contributory factors such as epithelial damage.