Avian and Human Influenza A Virus Receptors in Bovine Mammary Gland

Abstract

An outbreak of influenza A (H5N1) virus was detected in dairy cows in the United States. We detected influenza A virus sialic acid -α2,3/α2,6-galactose host receptors in bovine mammary glands by lectin histochemistry. Our results provide a rationale for the high levels of H5N1 virus in milk from infected cows.

Keywords: United States; cattle; host tropism; influenza; influenza A virus; receptor; sialic acid; viruses.

Figure 1

Results of staining showing wide expression of the human receptor for influenza A virus (designated SNA) in the bovine mammary gland. A) An example of the SNA staining of a mammary gland from a cow in late lactation. Arrowhead indicates expression of the human receptor in the active alveoli. Asterisks indicate less staining in the less active alveoli. Original magnification ×10. B, C) SNA staining of a duct (B) and (C) an alveolus in a 7-year-old cow. Original magnification ×60. D, E) Positive staining obtained from the image analysis. Green line shows the region of interest. Original magnification ×60. F) A neuraminidase pretreatment negative control showed markedly reduced staining of the SNA lectin. Original magnification ×60. The staining was visualized using Vector Blue (Vector Laboratories, https://vectorlabs.com).

Figure 2

Results of staining showing wide expression of the duck receptor for influenza A virus (designated MAA-II) in the alveoli of the bovine mammary gland. A) An example of the MAA-II staining of a mammary gland from a cow in late lactation. Arrowhead indicates expression of the duck receptor in active alveoli. Asterisks indicate less staining in the less active alveoli. Original magnification ×10. B, C) MAA-II staining of a duct (B) and an alveolus (C) in a 3-year-old cow. Original magnification ×60. D, E) Positive staining obtained from the image analysis. Green line shows the region of interest. Original magnification ×60. F) A neuraminidase pretreatment negative control showed markedly reduced staining of the MAA-II lectin in the alveolus but some nonspecific staining in the duct epithelium. The staining was visualized using Vector Blue (Vector Laboratories, https://vectorlabs.com). Original magnification ×60.

Figure 3

Pearson correlation coefficient showing a significant negative correlation between the percentage of SNA staining (bovine receptor) in the alveoli and the parity status of the cows (A) but not for MAA-II staining (duck receptor) (B). Original magnification ×60. Statistics and graphs made using GraphPad Prism version 10.2.3 (GraphPad Software, www.graphpad.com).