Form and density of M2 expression relative to PR8-infected MDCK cells. A. Doxycycline-induced HeLa-M2 and HeLa-C10 cells, without (No) or with (Yes) prior glutaraldehyde fixation, were solubilized. Cell extracts were electrophoresed under non-reducing conditions, blotted onto a PVDF membrane and tested for presence of M2 by staining with MAb 14C2-S1-4. MW shows the position of molecular weight markers. B. M2e-specific MAbs 14C2-S1-4 (squares) and M2-1 (triangles) were tested by ELISA for binding to HeLa-M2 (filled symbols), virus-infected MDCK cells (open symbols), nine hrs after infection with 10 TCID50 of PR8 per cell, and the corresponding control cell immunosorbents. Symbols show mean ± SEM of triplicate Δ ODs. A representative assay of several independent repeat experiments is shown. C. Sera from mice immunized with M2e-MAP were tested as in B for binding to HeLa-M2 (filled symbols) and PR8-infected MDCK cells (open symbols). Pooled sera from two different groups of mice (square, triangle) are shown. A representative assay of several independent experiments is shown.