Lectin Histochemistry for Influenza Receptors

The following biotinylated sialic acid-specific lectins were used to detect the avian and human influenza receptors [16 (link)]: biotinylated Maackia amurensis lectin I (MAA I); biotinylated Maackia amurensis lectin II (MAA II); and biotinylated Sambucus nigra agglutinin (SNA). MAA I (Cat# B-1315) and MAA II (Cat# B-1265) are markers for avian influenza virus receptors (AIV-R), while SNA (Cat# B-1305) is the marker for human influenza virus receptors (HuIV-R); the lectins were purchased from Vector Laboratories (Burlingame, CA, USA). Lectin histochemistry was performed, as described previously [17 (link)]. In brief, formalin-fixed, paraffin-embedded tissue sections were deparaffinized, immersed in 3% hydrogen peroxide and incubated with 5% bovine serum albumin, to block nonspecific staining. The tissue sections were then allowed to incubate overnight with SNA (1.5 μg/mL) and MAA (6 μg/mL) in buffer at 4 °C. An SABC kit (Dako, Carpinteria, CA, USA) was used to optimize the contrast between specific labeling and background. Biotinylated lectin binding was revealed by a 3,3′-diaminobenzidine tetrahydrochloride (DAB) substrate-chromogen kit (Zymed Labs, South San Francisco, CA, USA), which produced a brown color, and the slides were counterstained with hematoxylin. Omission of the lectins was used as a negative control.