Domestic mallards (Anas platyrhynchos domesticus) are traditionally used as a model to investigate infection dynamics and immune responses to low pathogenic avian influenza viruses (LPAIVs) in free-living mallards. However, it is unclear whether the immune response of domestic birds reflects the response of their free-living counterparts naturally exposed to these viruses. We investigated the extent to which the innate humoral immune response was similar among (i) wild-type domestic mallards in primary and secondary infection with LPAIV H4N6 in a laboratory setting (laboratory mallards), (ii) wild-type domestic mallards naturally exposed to LPAIVs in a semi-natural setting (sentinel mallards), and (iii) free-living mallards naturally exposed to LPAIVs. We quantified innate humoral immune function by measuring non-specific natural antibodies (agglutination), complement activity (lysis), and the acute phase protein haptoglobin. We demonstrate that complement activity in the first 3 days after LPAIV exposure was higher in primary-exposed laboratory mallards than in sentinel and free-living mallards. LPAIV H4N6 likely activated the complement system and the acute phase response in primary-exposed laboratory mallards, as lysis was higher and haptoglobin lower at day 3 and 7 post-exposure compared to baseline immune function measured prior to exposure. There were no differences observed in natural antibody and haptoglobin concentrations among laboratory, sentinel, and free-living mallards in the first 3 days after LPAIV exposure. Our study demonstrates that, based on the three innate humoral immune parameters measured, domestic mallards seem an appropriate model to investigate innate immunology of their free-living counterparts, albeit the innate immune response of secondary-LPAIV exposed mallards is a better proxy for the innate immune response in pre-exposed free-living mallards than that of immunologically naïve mallards.

国产野鸭（桔树）传统上用作研究自由活动野鸭中低致病性禽流感病毒（LPAIV）的感染动态和免疫反应的模型。但是，目前尚不清楚家禽的免疫反应是否反映了自然接触这些病毒的自由生存者的反应。我们研究了（i）在实验室环境下（LPAIV H4N6）初次和继发感染LPAIV H4N6的野生型野鸭之间的先天体液免疫反应的相似程度（ii）自然暴露于半自然环境中的LPAIV（前哨野鸭），以及（iii）自然暴露于LPAIV的自由生存野鸭。我们通过测量非特异性天然抗体（凝集），补体活性（裂解），和急性期蛋白触珠蛋白。我们证明，LPAIV暴露后的前3天，初次暴露的野鸭的补体活性高于前哨和自由生活的野鸭。LPAIV H4N6可能激活了初次暴露的野鸭的补体系统和急性期反应，因为与暴露前测定的基线免疫功能相比，暴露后第3天和第7天的溶解度更高，触珠蛋白降低。在LPAIV暴露后的前三天内，实验室，前哨和自由活动野鸭之间的天然抗体和触珠蛋白浓度没有差异。我们的研究表明，根据测得的三个先天体液免疫参数，野鸭似乎是研究其自由生活同伴的先天免疫学的合适模型，