Functional interactions between CD98 and β2 integrins (CD18).

(A) Aggregation was measured under standard conditions in the presence of CD98-AHN-18 (1.5 μg/mL, top panel), MEM 101A (CD29, 0.3 μg/mL, middle panel), or 161-46 (CD43, 0.3 μg/mL, bottom panel). Blocking antibodies to CD18 were added to U937 cultures 1 hour prior to the aggregating antibodies. Results are expressed as the percentage of aggregation relative to the aggregation in the absence of blocking antibody (column labeled 0 in each panel). Means that differ significantly from control (absence of inhibitory antibody,P < .05) are shown with an asterisk. Antibodies were tested at a series of dilutions, starting with the most dilute and increasing in 2-fold steps along the x-axis. To obtain the actual concentration of antibody at each point (in μg/mL), the x-axis value should be multiplied by 0.5 for both CLB-LFA1 (CD18, □) and BU86 (CD18, ■). (B) CD98 ligation does not alter cell-surface levels of CD18 or CD29. U937 cells were incubated in the presence of CD98-AHN-18 (1.5 μg/mL) or control for 24 hours (top panels) or 48 hours (bottom panels). Levels of cell-surface CD18 or CD29 were measured by flow cytometry as described in “Materials and methods.” Note that the 2 fluorescence histograms obtained in the presence and absence of CD98 are almost coincident. Histograms marked C are the fluorescence profile of CD98-treated cells stained with isotype control.