FIG. 4.

Host cellular PLG receptor A2 is associated with purified influenza virus particles. (A) IAV A/WSN/33, A/PR/8/34, A/Turkey/Massachussets/65 (H6N2), and A/Udorn/72 were produced in MDCK cells and then purified by different techniques as described in Materials and Methods (d, sucrose density purification; 2d, two successive sucrose density purifications; o, Optiprep purification; 2o, two successive Optiprep purifications; v, sucrose velocity purification; and v+d, sucrose density purification followed by sucrose velocity purification). Virions then were subjected to a 4 to 12% SDS-PAGE, followed by CBB staining. The main bands were excised from the CBB-stained gel and then were subjected to MALDI-TOF analysis. The proteins identified, indicated at the left of the gel panel, are the following: heat shock protein 70 (H70), the viral NP protein (NP), actin (Ac), A2, annexin I (A1), and viral matrix protein 1 (M1). (B) Proteins of the indicated purified IAV and IBDV virions were separated in 4 to 12% SDS-PAGE, blotted onto nitrocellulose membranes, and probed with the anti-A2, anti-p11, anti-ERK, and anti-NP antibodies as well as with an anti-VP3 IBDV monoclonal antibody. Aliquots of total proteins from MDCK cells left uninfected (−) or infected (+) with the PR/8/34 IAV strain were used as controls. The numbers at the right of the figure refer to molecular masses, in kilodaltons.