Deletion of talin1 in B lineage cells using CD19 Cre targeting abrogates integrin activation. (A) Schematic representation of Tln1 WT (Tln⁺), loxP flanked (Tln^fl), and deleted (Tln^null) alleles. The deletion of exons 1 to 4 takes place in B cells when Cre expression is driven by CD19. (B) Identification of Tln⁺ (657bp), Tln^fl(779bp), and Tln^null (707bp) alleles by polymerase chain reaction. (C) Immunoblot for talin1 and tubulin in B220⁺ and B220⁻ splenocytes derived from CD19^Cre/+Tln1^fl/fl mice. (D) FACS staining for expression of α₄ and α_L integrins in spleen-derived B cells from WT or CD19^Cre/+Tln1^−/fl (talin null) mice. For clarity, all isotype-matched negative controls, which yielded fluorescence intensity levels less than 10 arbitrary units, were omitted. (E) Frequency of arrest of WT and Tln1^−/− B cells on VCAM-1 or on ICAM-1 triggered by 1-minute exposure to phorbol myristate acetate. Arrests were measured at a shear stress of 0.75 dyne/cm² (VCAM-1) or 0.5 dyne/cm² (ICAM-1). Results are the mean values ± range of 2 fields of view in 1 experiment representative of 4 independent experiments.