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The role of the interaction of CD2 molecules with lymphocyte function-associated antigen 3 (LFA-3) in facilitating nominal antigen recognition by T lymphocytes was studied by utilizing an HLA-DR4-restricted CD4+ cytotoxic human T-cell clone specific for human immunodeficiency virus envelope glycoprotein gpl20 as a responder and murine flbroblasts transfected with human class II major histocompatibility complex (MHC) and/or human LFA-3 molecules as antigenpresenting cells (APC). Although expression of the DR4 restriction element in fibroblasts is sufficient for T-cell recognition of a gpl20 peptide as judged by induction of proliferation, coexpression of human LFA-3 on DR4+ APC decreases the molar requirement of nominal antigen by greater than one order ofmagnitude. Both LFA-3 and the relevant class H MHC molecules are necessary for antigen-independent conjugate formation, but the binding is further enhanced by specific nominal antigen. CD2-LFA-3 interaction is independent of T-cell receptor-MHC interaction and contributes directly to the stabilized conjugate between the T cell and LFA-3-bearing APC; soluble CD2 and monoclonal antibodies to LFA-3 and CD2 reduce T-cell-APC binding to the level mediated by nominal antigen and MHC. During conjugate formation, CD2 but not CD3 molecules are reorganized into the cell-cell interaction site in an antigen-independent manner. Thus, reorganization and/or coassociation of CD2 with CD3 molecules is not essential for T-cell activation.The ability ofT lymphocytes to recognize specific antigens in the context of class I and class II major histocompatibility complex (MHC) molecules is determined by the unique clonotypic T-cell receptor (TCR)-CD3 complex which they individually bear. The process of antigen recognition involves the physical interaction of a TCR with a nominal peptide antigen bound to a specific MHC molecule referred to as a restricting element. This process is not singularly dictated by the TCR complex itself, but rather is dependent on other structures, including CD4, CD8, CD2, and lymphocyte function-associated antigen 1 (LFA-1) (reviewed in refs. 1-3). CD4 and CD8 structures bind to monomorphic regions of class II and class I MHC structures, respectively, thereby facilitating the interaction of the TCR with the MHC restricting element (reviewed in ref. 4). In addition to the MHC binding accessory structures, a set of adhesion structures facilitates non-antigen-specific interactions between T lymphocytes and their cognate partners. This set includes the CD2/lymphocyte function-associated antigen 3 (LFA-3) receptor-ligand pair (5, 6).Studies employing antibodies directed against CD2 or LFA-3 as well as murine T-cell hybridoma transfectants expressing human CD2 have suggested that CD2-LFA-3 interaction is important for the T-cell recognition process (7,8). However, virtually nothing is known about the mechanism by which CD2-LFA-3 interaction augments T-cell recognition-in particular, whether the interaction influences recognition of nominal antigen and whet...

Introduction:Evidence strongly suggests that soluble oligomers of amyloid beta protein (oAβ) help initiate the pathogenic cascade of Alzheimer's disease (AD). To date, there have been no validated assays specific for detecting and quantifying oAβ in human blood. Methods:We developed an ultrasensitive oAβ immunoassay using a novel capture antibody (71A1) with N-terminal antibody 3D6 for detection that specifically quantifies soluble oAβ in the human brain, cerebrospinal fluid (CSF), and plasma.Results: Two new antibodies (71A1; 1G5) are oAβ-selective, label Aβ plaques in nonfixed AD brain sections, and potently neutralize the synaptotoxicity of AD brainderived oAβ. The 71A1/3D6 assay showed excellent dilution linearity in CSF and plasma without matrix effects, good spike recovery, and specific immunodepletion. Discussion:We have created a sensitive, high throughput, and inexpensive method to quantify synaptotoxic oAβ in human plasma for analyzing large cohorts of aged and AD subjects to assess the dynamics of this key pathogenic species and response to therapy.