Alterations of the receptor-binding properties of swine influenza A viruses (SIVs) during their isolation in embryonated chicken eggs have not been well studied. In this study, the receptorbinding properties of classical H1 SIVs isolated solely in eggs or Madin-Darby canine kidney (MDCK) cells were examined. Sequencing analysis revealed substitutions of D190V/N or D225G in the haemagglutinin (HA) proteins in egg isolates, whereas MDCK isolates retained HA genes identical to those of the original viruses present in the clinical samples. Egg isolates with substitution of either D190V/N or D225G had increased haemagglutinating activity for mouse and sheep erythrocytes, but reduced activity for rabbit erythrocytes. Additionally, egg isolates with D225G had increased haemagglutination activity for chicken erythrocytes. A direct binding assay using a sialyl glycopolymer that possessed either a 5-N-acetylneuraminic acid (Neu5Ac) a2,6galactose (Gal) or a Neu5Aca2,3Gal linkage revealed that the egg isolates used in this study showed higher binding activity to the Neu5Aca2,3Gal receptor than MDCK isolates. Increased binding activity of the egg isolates to the Neu5Aca2,3Gal receptor was also confirmed by haemagglutination assay with resialylated chicken erythrocytes by Galb1,3/4GlcNAca2,3-sialyltransferase. These observations were reinforced by flow-cytometric and N-glycan analyses of the erythrocytes. The a2,3-linked sialic acids were expressed predominantly on the surface of mouse and sheep erythrocytes. Chicken erythrocytes expressed Neu5Aca2,3Gal more abundantly than Neu5Aca2,6Gal, and rabbit erythrocytes expressed both 5-N-glycolylneuraminic acid (Neu5Gc) a2,6Gal and Neu5Aca2,6Gal. Our results demonstrate clearly that classical H1 SIVs undergo alterations in receptor-binding activity associated with an amino acid substitution in the HA protein during isolation and propagation in embryonated chicken eggs.
Perinatal transmission plays a critical role in the spread of bovine leukemia virus (BLV) infection in cattle herds. In the Holstein breed, we previously identified BLV resistant and susceptible bovine leukocyte antigen (BoLA)-DRB3 alleles, including BoLA-DRB3*009:02 and *014:01:01 with a low BLV proviral load (PVL), and *015:01 and *012:01 with a high PVL. Here, we evaluated the perinatal BLV transmission risk in dams with different BoLA-DRB3 alleles. BoLA-DRB3 alleles of 120 dam-calf pairs from five dairy farms in Japan were identified; their PVL was quantified using the BLV-Coordination of Common Motifs (CoCoMo)-qPCR-2 assay. Ninety-six dams were BLV-positive, and 29 gave birth to BLV-infected calves. Perinatal transmission frequency was 19% in dams with resistant alleles suppressed to a low PVL level, and 38% and 25% in dams with susceptible and neutral alleles that maintained high PVL levels, respectively. Notably, all calves with resistant alleles were BLV free, whereas 30% of calves with susceptible genes were infected. Thus, vertical transmission risk was extremely lower for dams and calves with resistant alleles compared to those with susceptible alleles. Our results can inform the development of effective BLV eradication programs under field conditions by providing necessary data to allow for optimal selection of dams for breeding.
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