Impaired integrin activation in leukocytes from homozygous carriers of the CalDAG-GEFI S381F and R113X mutations. (A,B) β₂ integrin activation. Neutrophils were kept resting or were stimulated with the indicated agonists in the presence of (A) Alexa Fluor 488-fibrinogen or (B) m24 antibody to determine the activation state of α_Mβ₂ and α_Lβ₂, respectively. C) Granule secretion. Neutrophils were kept resting or were stimulated with N-formylmethionyl-leucyl-phenylalanine (fMLP; 1 mM) or PMA (100 nM) in the presence of a phycoerythrin-labeled antibody to CD11b (Mac-1). Results are expressed as the mean fold increase, plus standard error, in median fluorescence intensity from data obtained in the 3 homozygous patients (black bars) and 3 healthy controls (gray bars).