Porcine epidemic diarrhea virus (PEDV) causes severe clinical diarrhea in neonatal piglets, with reported mortality rates between 70–100%. The humoral immunity, especially the local intestinal IgA responses, plays an important role in the immune protection against PEDV infection. In this study, we evaluated the isotype antibody responses against the PEDV nucleocapsid (N) protein and the spike (S) protein subunits 1 (S1) and 2 (S2) in the serum and intestine of piglets. We also determined its serum neutralizing activity against the PEDV field strain HBMC2012 in 21-day-old piglets. Enzyme-linked immunosorbent assays (ELISA) revealed that the production of IgM against the N protein and S1 subunit was higher compared to the S2 subunit. The anti-S2 IgA antibodies were higher than the anti-N protein and anti-S1 IgA at 3 days post-infection (dpi). The specific IgA responses to the S2 subunit were higher than the responses observed in S1. The specific IgG responses against S1 and S2 subunits exceeded those of N protein. The serum neutralizing activities against PEDV were relatively low with a tendency to decline over time. No isotype-specific antibodies were found in the intestinal contents from infected pigs, except the one with weak IgA responses against N protein at 28 dpi. Immunohistochemical staining showed that a few IgM, IgA, and IgG antibody-secreting cells were mainly located in the mucosa of the duodenum and ileum of PEDV-infected pigs at 3 dpi. This study suggests poor systemic and intestinal isotype-specific antibody responses, especially those of IgA, and weak serum neutralizing activities against the field PEDV strain in piglets.

猪流行性腹泻病毒（PEDV）在新生仔猪中引起严重的临床腹泻，据报道死亡率在70-100％之间。体液免疫，特别是局部肠道IgA反应，在抵抗PEDV感染的免疫保护中起着重要作用。在这项研究中，我们评估了仔猪血清和肠道中针对PEDV核衣壳（N）蛋白和突峰（S）蛋白亚基1（S1）和2（S2）的同种型抗体反应。我们还确定了其对21日龄仔猪中PEDV田间株HBMC2012的血清中和活性。酶联免疫吸附试验（ELISA）显示，与S2亚基相比，针对N蛋白和S1亚基的IgM产量更高。感染后3天（dpi），抗S2 IgA抗体高于抗N蛋白和抗S1 IgA。对S2亚基的特异性IgA反应高于在S1中观察到的反应。针对S1和S2亚基的特异性IgG反应超过了N蛋白。针对PEDV的血清中和活性相对较低，并且会随着时间的流逝而下降。除了感染28 dpi时对N蛋白的IgA反应较弱的猪以外，在感染猪的肠内容物中未发现同种型特异性抗体。免疫组织化学染色显示，在感染后3 dpi时，一些IgM，IgA和IgG抗体分泌细胞主要位于PEDV感染猪的十二指肠和回肠粘膜中。这项研究表明，全身和肠道同种型特异性抗体反应较弱，尤其是IgA抗体应答，而对猪中田间PEDV株的血清中和活性较弱。