Data from: Helminth interaction with the host immune system: short-term benefits and costs in relation to the infectious environment

Chronic infections imply that the parasite and the host immune system closely interact for a long time without a fatal outcome. Environmental changes encountered by hosts and parasites, such as coinfections, can deeply affect the stability of this apparent equilibrium. Our study aimed to determine the effect of the infectious environment on the costs and benefits of chronic infection with the gut nematode Heligmosomoides polygyrus in mice. Heligmosomoides polygyrus is known for its capacity to actively interfere with the host immune response by secreting molecules that can dampen immunity. We simulated bacterial coinfection of H. polygyrus-infected CBA-strain mice during the chronic phase of the infection by injecting them with Escherichia coli lipopolysaccharide. We found that infection by H. polygyrus induced only weak costs for the host (in terms of reproductive investment) and was characterized by the upregulation of both Th1 (interferon-γ) and anti-inflammatory (transforming growth factor-β) cytokines, which is favorable to parasite persistence. However, when co-occurring with the simulated bacterial infection, H. polygyrus infection was associated with a pronounced shift toward a pro-inflammatory status, which was deleterious to both the parasite and the host. Our study highlights the dynamic equilibrium reached during chronic infection, where a rapid environmental change, such as a concomitant bacterial infection, can deeply affect the outcome of the host-parasite interaction.

慢性感染是指寄生虫与宿主免疫系统长期紧密互作且未引发宿主致死性结局的感染状态。宿主与寄生虫所面临的环境扰动（如合并感染）可深刻影响这一表观平衡的稳定性。本研究旨在探究感染环境对小鼠肠道线虫多氏泡首线虫（Heligmosomoides polygyrus）慢性感染的成本与收益的影响。已知多氏泡首线虫可通过分泌免疫抑制分子主动干预宿主免疫应答。本研究通过向处于慢性感染阶段、已感染多氏泡首线虫的CBA品系小鼠注射大肠杆菌脂多糖（Escherichia coli lipopolysaccharide），模拟细菌合并感染模型。研究发现，单纯多氏泡首线虫感染仅会对宿主造成微弱的生存成本（以生殖投入为衡量指标），且宿主免疫特征为Th1型（干扰素-γ，interferon-γ）与抗炎型（转化生长因子-β，transforming growth factor-β）细胞因子均上调，该状态有利于寄生虫的长期定植。然而，当合并模拟的细菌感染时，多氏泡首线虫感染会伴随宿主免疫向促炎状态的显著转变，这一变化对寄生虫与宿主均具有危害性。本研究凸显了慢性感染过程中形成的动态平衡：诸如伴随性细菌感染这类快速环境扰动，可深刻改变宿主-寄生虫互作的最终结局。