The Role of B-cells and IgM Antibodies in Parasitemia, Anemia, and VSG Switching in Trypanosoma brucei–Infected Mice

African trypanosomes are extracellular parasitic protozoa, predominantly transmitted by the bite of the haematophagic tsetse fly. The main mechanism considered to mediate parasitemia control in a mammalian host is the continuous interaction between antibodies and the parasite surface, covered by variant-specific surface glycoproteins. Early experimental studies have shown that B-cell responses can be strongly protective but are limited by their VSG-specificity. We have used B-cell (µMT) and IgM-deficient (IgM−/−) mice to investigate the role of B-cells and IgM antibodies in parasitemia control and the in vivo induction of trypanosomiasis-associated anemia. These infection studies revealed that that the initial setting of peak levels of parasitemia in Trypanosoma brucei–infected µMT and IgM−/− mice occurred independent of the presence of B-cells. However, B-cells helped to periodically reduce circulating parasites levels and were required for long term survival, while IgM antibodies played only a limited role in this process. Infection-associated anemia, hypothesized to be mediated by B-cell responses, was induced during infection in µMT mice as well as in IgM−/− mice, and as such occurred independently from the infection-induced host antibody response. Antigenic variation, the main immune evasion mechanism of African trypanosomes, occurred independently from host antibody responses against the parasite's ever-changing antigenic glycoprotein coat. Collectively, these results demonstrated that in murine experimental T. brucei trypanosomiasis, B-cells were crucial for periodic peak parasitemia clearance, whereas parasite-induced IgM antibodies played only a limited role in the outcome of the infection

The environmental impacts of palm oil in context

Delivering the Sustainable Development Goals (SDGs) requires balancing demands on land between agriculture (SDG 2) and biodiversity (SDG 15). The production of vegetable oils, and in particular palm oil, illustrates these competing demands and trade-offs. Palm oil accounts for 40%1 of the current global annual demand for vegetable oil as food, animal feed, and fuel (210 million tons2 (Mt)), but planted oil palm covers less than 5-5.5%3 of total global oil crop area (ca. 425 Mha)4 , due to oil palm’s relatively high yields5. Recent oil palm expansion in forested regions of Borneo, Sumatra, and the Malay Peninsula, where >90% of global palm oil is produced, has led to substantial concern around oil palm’s role in deforestation. Oil palm expansion’s direct contribution to regional tropical deforestation varies widely, ranging from 3% in West Africa to 47% in Malaysia. Oil palm is also implicated in peatland draining and burning in Southeast Asia. Documented negative environmental impacts from such expansion include biodiversity declines, greenhouse gas emissions, and air pollution. However, oil palm generally produces more oil per area than other oil crops, is often economically viable in sites unsuitable for most other crops, and generates considerable wealth for at least some actors. Global demand for vegetable oils is projected to increase by 46% by 2050. Meeting this demand through additional expansion of oil palm versus other vegetable oil crops will lead to substantial differential effects on biodiversity, food security, climate change, land degradation, and livelihoods. Our review highlights that, although substantial gaps remain in our understanding of the relationship between the environmental, socio-cultural and economic impacts of oil palm, and the scope, stringency and effectiveness of initiatives to address these, there has been little research into the impacts and trade-offs of other vegetable oil crops. Greater research attention needs to be given to investigating the impacts of palm oil production compared to alternatives for the trade-offs to be assessed at a global scale. Over the past 25 years, global oil crops have expanded rapidly, with major impacts on land use. The land used for growing oil crops grew from 170 million ha (Mha) in 1961 to 425 Mha in 2017 or ~30% of all cropland world-wide. Oil palm, soy, and rapeseed together account for >80% of all vegetable oil production with cotton, groundnuts, sunflower, olive, and coconut comprising most of the remainder (Table 1, Figure 1). These crops, including soy (125 Mha planted area) and maize (197 Mha planted area), are also used as animal feed and other products. Oil palm is the most rapidly expanding oil crop. This palm originates from equatorial Africa where it has been cultivated for millennia, but it is now widely grown in Southeast Asia. Between 2008 and 2017, oil palm expanded globally at an average rate of 0.7 Mha per year, and palm oil is the leading and cheapest edible oil in much of Asia and Africa. While it has been estimated that palm oil is an ingredient in 43% of products found in British supermarkets, we lack comparable studies for the prevalence of other oils. As a wild plant, the oil palm is a colonising species that establishes in open areas. Cultivated palms are commonly planted as monocultures, although the tree is also used in mixed, small-scale and agroforestry settings. To maximize photosynthetic capacity and fruit yields, oil palm requires a warm and wet climate, high solar radiation, and high humidity. It is thus most productive in the humid tropics, while other oil crops, except coconut, grow primarily in subtropical and temperate regions (Table 1). Moreover, because oil palm tolerates many soils including deep peat and sandy substrates, it is often profitable in locations where few other commodity crops are viable. The highest yields from planted oil palm have been reported in Southeast Asia5 . Yields are generally lower in Africa and the Neotropics, likely reflecting differences in climatic conditions including humidity and cloud cover, as well as management, occurrence of pests and diseases, and planting stock. Palm oil is controversial due to its social and environmental impacts and opportunities. Loss of natural habitats, reduction in woody biomass, and peatland drainage that occur during site preparation are the main direct environmental impacts from oil palm development. Such conversion typically reduces biodiversity and water quality and increases greenhouse gas emissions, and, when fire is used, smoke and haze. Industrial oil palm expansion by large multi-national and national companies is also often associated with social problems, such as land grabbing and conflicts, labour exploitation, social inequity16 and declines in village-level well-being. In producer countries, oil palm is a valued crop that brings economic development to regions with few alternative agricultural development options, and generates substantial average livelihood improvements when smallholder farmers adopt oil palm. Here we review the current understanding of the environmental impacts from oil palm cultivation and assess what we know about other oil crops in comparison. Our focus is on biodiversity implications and the environmental aspects of sustainability, and we acknowledge the importance of considering these alongside socio-cultural, political, and economic outcomes