Immunoblots showing chitin binding of Sp22D from cell lines. 3B/FCS− (A), 3A/FCS− (B), and 3A/FCS+ (C), conditioned medium supernatants (lanes C) were mixed with chitin beads, which were washed and eluted at progressively lower pH (5.0 and 2.0); flow-through (ft) and PBS washes (w) also are shown. The 160- to 170-kDa polypeptides of 3B/FCS− and 3A/FCS+ samples bind tightly and are eluted from chitin only at pH 2.0. Smaller polypeptides, including all components of the 3A/FCS− samples, do not bind.