Immunofluorescence analysis of cytokine binding to lymphocyte cell-surface HS. (A) Mock- (control) or (B) heparitinase-digested (+ h’ase) F10 cells were stained and analyzed by two-color flow cytometry. Biotinylated 10E4 (followed by streptavidin-red 613) recognizes native cell-surface HS while 3G10 (FITC) detects heparitinase-cleaved HS. (C) The capacity of these B-cell precursors to bind biotinylated IL-7 or the negative control reagent, biotinylated soybean trypsin inhibitor (STI), followed by avidin-fluorescein, was subsequently assessed. (D) Binding of biotinylated IL-2 to control or heparitinase-treated CTLL-2 cells; the binding profiles directly overlap. (E) Control or heparitinase-digested F10 lymphocytes were stained with an antibody to the IL-7 receptor  chain (SB/14) or rat IgG_2a followed by goat anti-rat Ig-FITC.