ABSTRACT
Kindlin-3 is a key lymphocyte function-associated antigen-1 (LFA-1) coactivator deleted in leukocyte adhesion deficiency-III (LAD-III). In the present study, we investigated the involvement of this adaptor in lymphocyte motility and TCR-triggered arrest on ICAM-1 or on dendritic cells (DCs). Kindlin-3-null primary T cells from a LAD-III patient migrated normally on the major lymph node chemokine CCL21 and engaged in normal TCR signaling. However, TCR activation of Kindlin-3-null T lymphocytes failed to trigger the robust LFA-1-mediated T-cell spreading on ICAM-1 and ICAM-1-expressing DCs that is observed in normal lymphocytes. Kindlin-3 was also essential for cytoskeletal anchorage of the LFA-1 heterodimer and for microclustering of LFA-1 within ventral focal dots of TCR-stimulated lymphocytes spread on ICAM-1. Surprisingly, LFA-1 on Kindlin-3-null lymphocytes migrating over CCL21 acquired normal expression of an epitope associated with the conformational activation of the key headpiece domain, ß I. This activated LFA-1 was highly responsive to TCR-triggered ICAM-1-driven stop signals in normal T cells locomoting on CCL21, but not in their Kindlin-3-null T-cell counterparts. We suggest that Kindlin-3 selectively contributes to a final TCR-triggered outside-in stabilization of bonds generated between chemokine-primed LFA-1 molecules and cell-surface ICAM-1.
Subject(s)
Cell Communication , Dendritic Cells/immunology , Intercellular Adhesion Molecule-1/metabolism , Lymphocyte Function-Associated Antigen-1/metabolism , Membrane Proteins/metabolism , Neoplasm Proteins/metabolism , Receptors, Antigen, T-Cell/metabolism , T-Lymphocytes/metabolism , Cell Adhesion , Cell Movement , Cell Shape , Cells, Cultured , Chemokine CCL21/metabolism , Cytoskeleton/metabolism , Dendritic Cells/metabolism , Dendritic Cells/ultrastructure , Humans , Immunological Synapses/immunology , Leukocyte-Adhesion Deficiency Syndrome/immunology , Leukocyte-Adhesion Deficiency Syndrome/metabolism , Leukocyte-Adhesion Deficiency Syndrome/pathology , Lymphocyte Activation , Membrane Microdomains/immunology , Membrane Proteins/deficiency , Membrane Proteins/genetics , Microvilli/metabolism , Microvilli/ultrastructure , Neoplasm Proteins/deficiency , Neoplasm Proteins/genetics , Protein Multimerization , Protein Transport , Signal Transduction , T-Lymphocytes/immunology , T-Lymphocytes/ultrastructureABSTRACT
Talin1 is a key integrin coactivator. We investigated the roles of this cytoskeletal adaptor and its target integrins in B-cell lymphogenesis, differentiation, migration, and function. Using CD19 Cre-mediated depletion of talin1 selectively in B cells, we found that talin1 was not required for B-cell generation in the bone marrow or for the entry of immature B cells to the white pulp of the spleen. Loss of talin1 also did not affect B-cell maturation into follicular B cells but compromised differentiation of marginal zone B cells. Nevertheless, serum IgM and IgG levels remained normal. Ex vivo analysis of talin1-deficient spleen B cells indicated a necessary role for talin1 in LFA-1 and VLA-4 activation stimulated by canonical agonists, but not in B-cell chemotaxis. Consequently, talin1 null B splenocytes could not enter lymph nodes nor return to the bone marrow. Talin1 deficiency in B cells was also impaired in the humoral response to a T cell-dependent antigen. Collectively, these results indicate that talin1 is not required for follicular B-cell maturation in the spleen or homeostatic humoral immunity but is critical for integrin-dependent B lymphocyte emigration to lymph nodes and optimal immunity against T-dependent antigens.
Subject(s)
B-Lymphocytes/cytology , B-Lymphocytes/immunology , Bone Marrow/growth & development , Integrins/metabolism , Lymph Nodes/cytology , Spleen/cytology , Talin/physiology , Animals , Bone Marrow/immunology , Cell Adhesion , Cell Differentiation , Cell Proliferation , Cells, Cultured , Chemotaxis, Leukocyte , Female , Flow Cytometry , Immunization , Integrin alpha4beta1/metabolism , Lymph Nodes/immunology , Lymphocyte Function-Associated Antigen-1/metabolism , Male , Mice , Mice, Knockout , Spleen/immunologyABSTRACT
Leukocyte adhesion deficiency (LAD)-III is associated with homozygous stop codon mutations in Kindlin-3, the hematopoietic member of the Kindlin family of integrin coactivators. In addition, a subgroup of LAD-III patients has a homozygous splice junction mutation in and reduced expression of the Rap-1 guanine nucleotide exchange factor, CalDAG-GEFI (CDGI). In this study, we compared the adhesive properties of the leukocyte function-associated antigen-1 (LFA-1) and very late activation antigen-4 (VLA-4) integrins in both primary and activated leukocytes derived from these 2 LAD-III subgroups. Primary lymphocytes lacking both Kindlin-3 and CDGI lost all firm T-cell receptor-stimulated LFA-1 adhesiveness, in contrast to LAD-III lymphocytes deficient in Kindlin-3 alone. Effector T cells expanded from all tested LAD-III variants expressed normal CDGI, but lacked Kindlin-3. These Kindlin-3-null effector T cells exhibited total loss of inside-out LFA-1 activation by chemokine signals as well as abrogated intrinsic LFA-1 adhesiveness. Surprisingly, VLA-4 in Kindlin-3-null resting or effector lymphocytes retained intrinsic rolling adhesions to vascular cell adhesion molecule-1 and exhibited only partial defects in chemokine-stimulated adhesiveness to vascular cell adhesion molecule-1. Deletion of the putative beta(1) Kindlin-3 binding site also retained VLA-4 adhesiveness. Thus, our study provides the first evidence that Kindlin-3 is more critical to LFA-1 than to VLA-4-adhesive functions in human lymphocytes.
