Immune function in Amazonian horticulturalists

Abstract

Background Amazonian populations are exposed to diverse parasites and pathogens, including protozoal, bacterial, fungal, and helminthic infections. Yet much of our understanding of the immune system is based on industrialised populations where these infections are relatively rare. Aim We examine distributions and age-related differences in 22 measures of immune function for Bolivian forager-horticulturalists and US and European populations. Subjects and Methods Subjects were 6,338 Tsimane aged 0–90 years. Blood samples collected between 2004–2014 were analysed for 5-part blood differentials, C-reactive protein, erythrocyte sedimentation rate (ESR), and total immunoglobulins E, G, A, and M. Flow cytometry was used to quantify naive and non-naïve CD4 and CD8 T cells, natural killer cells, and B cells. Results Compared to reference populations, Tsimane have elevated levels of most immunological parameters, particularly immunoglobulins, eosinophils, ESR, B cells, and natural killer cells. However, monocytes and basophils are reduced and naïve CD4 cells depleted in older age groups. Conclusion Tsimane ecology leads to lymphocyte repertoires and immunoglobulin profiles that differ from those observed in industrialised populations. These differences have consequences for disease susceptibility and co-vary with patterns of other life history traits, such as growth and reproduction.

High resting metabolic rate among Amazonian forager‐horticulturalists experiencing high pathogen burden

“…On average, 20% of WBCs are eosinophils, also indicative of intense parasitic infection, compared with the normal US reference range of <5%, with >90% of Tsimane adults in the clinically high range. Natural killer cells and B cell counts are approximately twice as high as typical US values (Blackwell et al 2016). Tsimane also demonstrate higher levels of inflammation than those found in industrialized populations.…”

“…The costs of immune activation can be substantial: Tsimane adults with clinical symptoms of intestinal helminth infection have excess RMR of 116-138 kcals/d (Table S4). Elevated WBC counts are 10 times more prevalent among Tsimane than Americans; Tsimane WBCs are 2,600 cells/uL higher on average than US levels among adults age 18-49 (Blackwell et al 2016), which in our model adds 23-28 excess RMR kcals/day. These findings build upon results from studies in Western populations showing RMR increases with infection (Muehlenbein et al 2010).…”

“…WBCs also decline with age among Tsimane, particularly lymphocytes and eosinophils, suggesting increasing maintenance costs because older adults are not less likely to experience infection than younger adults (Gurven et al 2009). Systemic immunity shows many indications of chronic activation from infection with helminths, with 70% of Tsimane infected at any given time (Blackwell et al 2011; Blackwell et al 2013; Blackwell et al 2015; Blackwell et al 2016); coinfection is not uncommon (Blackwell et al 2013; Martin et al 2013). Serum immunoglobulins are two orders of magnitude higher than among US adults, especially for IgE (highly indicative of infection with helminths) (Blackwell et al 2011).…”

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

“…Intestinal helminths are lipophilic and absorb lipids either from their host’s gut contents or blood stream, either of which could reduce their host’s circulating lipids and thereby minimize accumulation of plaques in vasculature [36]. Additionally, endo-parasites like helminths represent a significant energetic cost from immune activation that increase resting metabolic rates, further limiting adipose tissue deposition [37, 38]. These helminths were likely a prevalent source of infection over human evolutionary history.…”

Human Biology of the Amazon

“…The authors noted the limited number of studies on these kinds of groups and call for additional research and public health policies to improve their qualityof-life and health. Blackwell et al (2016) address the complex issue of how the human immune system responds to rural Amazonian environments. They examined 22 measures of immune function and found that Tsimane' of all age groups show elevations in most measures of immune function in comparison to reference populations.…”