Characterization of a novel monoclonal antibody with restricted specificity to the free beta 2 integrin alpha M CD11b subunit.
ABSTRACT Leukocyte cell surface expression and function of beta2 integrins require the intracellular association of alpha subunits, CD11a, b, c, d, respectively, with the common CD18 beta2 subunit. We have raised and characterized a murine MAb -- ME-MDF -- directed against the low affinity form of the human integrin alphaM subunit CD11b A-domain. MAb ME-MDF is an IgG2a that has a kDa of 2,45461 +/- 0.12 x 10(-9) M. MAb ME-MDF recognizes both the low and high affinity forms of the CD11b A-domain. Flow cytometry showed that ME-MDF does not recognize the heterodimeric CD11b/CD18 molecule at the surface of polymorphonuclear cells and the human monoblast cell line U937. Western blot analysis of U937 cell line cell surface proteins demonstrated that ME-MDF reacts specifically with the CD11b subunit but does not react with the heterodimeric CD11b/CD18 complex, a feature that differentiates it from other CD11b A-dom-specific MAbs. These observations suggest that ME-MDF recognizes an epitope that is involved in the association of the two subunits and hence is not accessible within the heterodimeric form of the CD11b/CD18 molecule. These data show that the CD11b A-dom engages not only the MIDAS but also the ME-MDF-specific epitope to associate with the CD18 subunit. We have also constructed, and expressed in the yeast Pichia pastoris, the corresponding recombinant scFv form of MAb ME-MDF and characterized the CDRs. MAb ME-MDF is characterized by short VH and VL CDR3. MAb ME-MDF and/or its recombinant scFv form would be very useful to study the structural basis of the association between the alpha and beta2 integrin subunits and to investigate the possibility of modulating CR3 cell surface expression by preventing subunit association.
- Cell 08/1990; 62(1):3-6. · 31.96 Impact Factor
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ABSTRACT: A variety of cell adhesion mechanisms underlie the way that cells are organized in tissues. Stable cell interactions are needed to maintain the structural integrity of tissues, and dynamic changes in cell adhesion participate in the morphogenesis of developing tissues. Stable interactions actually require active adhesion mechanisms that are very similar to those involved in tissue dynamics. Adhesion mechanisms are highly regulated during tissue morphogenesis and are intimately related to the processes of cell motility and cell migration. In particular, the cadherins and the integrins have been implicated in the control of cell movement. Cadherin mediated cell compaction and cellular rearrangements may be analogous to integrin-mediated cell spreading and motility on the ECM. Regulation of cell adhesion can occur at several levels, including affinity modulation, clustering, and coordinated interactions with the actin cytoskeleton. Structural studies have begun to provide a picture of how the binding properties of adhesion receptors themselves might be regulated. However, regulation of tissue morphogenesis requires complex interactions between the adhesion receptors, the cytoskeleton, and networks of signaling pathways. Signals generated locally by the adhesion receptors themselves are involved in the regulation of cell adhesion. These regulatory pathways are also influenced by extrinsic signals arising from the classic growth factor receptors. Furthermore, signals generated locally be adhesion junctions can interact with classic signal transduction pathways to help control cell growth and differentiation. This coupling between physical adhesion and developmental signaling provides a mechanism to tightly integrate physical aspects of tissue morphogenesis with cell growth and differentiation, a coordination that is essential to achieve the intricate patterns of cells in tissues.Cell 03/1996; 84(3):345-57. · 31.96 Impact Factor
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ABSTRACT: A recombinant peptide encoding the CD11b A domain bound 54Mn2+ with a high affinity. Other divalent cations, including Mg2+, Zn2+, Ni2+, Co2+, and Cd2+, but not Ca2+ or Ba2+, competed effectively for Mn2+ binding. Amino acid substitutions within two conserved and noncontiguous regions in the recombinant peptide abolished 54Mn2+ binding. When these substitutions were introduced independently in complement receptor type 3 (CR3), each abolished the metal-dependent binding of the receptor to the major C3 opsonin iC3b, without impairing subunit association or surface expression of the receptor. These findings identify an unsuspected and novel metal-binding site within the A domain of CR3 that is required for metal-dependent ligand binding and also identify a good target for designing drugs aimed at countering the inflammatory potential of this key receptor.Cell 04/1993; 72(6):857-67. · 31.96 Impact Factor