Structural analysis of the human immunodeficiency virus-binding domain of CD4. Epitope mapping with site-directed mutants and anti-idiotypes.

Abstract

CD4 is a 55-kD glycoprotein found predominantly on the surface of a subset of T lymphocytes. This monomeric surface protein has an extracellular region of 372 amino acids, a single transmembrane segment of 21 residues, and a short cytoplasmic region of40 residues . The extracellular region consists of four tandem domains that have sequence and predicted structural homology with Ig L chain V regions (1, 2). On lymphocytes, CD4 defines T cells that recognize antigen presented by MHC class II-bearing cells. In this interaction, CD4 appears to promote efficient T cell activation through binding to a monomorphic determinant on the class II proteins of the presenting cell . This association with class II proteins may increase the avidity of the interaction between the T cell and APC (3-5). However, the recently observed association of the T cell-specific tyrosine kinase p56ick with CD4 (6, 7) also suggests a direct role for CD4 in signal transduction in response to antigen presentation. This potentially complex role ofCD4 may explain the reported inhibition (8-16) or enhancement (17-19) of the T cell response in vitro by different CD4 mAbs .In man, CD4 is also the target for virus attachment by HIV (20-22), a process mediated by the viral envelope glycoprotein gp120 (23). Through extensive genetic analysis, the binding site for gp120 on CD4 was localized within the first Ig-like domain, V1, to a predicted loop structure of ti 12 amino acids (24-28). Based on the sequence alignment of V, with human tc chain V domains (V,,), we and others (24-28) have proposed that the gp120-binding site encompasses a region within Vt that corresponds to the complimentarity-determining region 2 (CDR2)1 of Ig L chains. In this report we provide evidence for this model of the V1 domain through epitope mapping of a panel of 26 CD4 mAbs .

Recombinant Anti-CD4 Antibody 13B8.2 Blocks Membrane-Proximal Events by Excluding the Zap70 Molecule and Downstream Targets SLP-76, PLCγ1, and Vav-1 from the CD4-Segregated Brij 98 Detergent-Resistant Raft Domains

“…Epitope specificity governing raft localization and further biological effects have mainly been defined for anti-CD20 reagents (5,6,16). It would be interesting to compare the epitope specificity of anti-CD4 Abs YNB.46 (30), KT6, YTS177, and YTA3.1 (31,32), all of which are known to induce inhibition of Zap70 phosphorylation, with the CDR3-like epitope specificity (residues Glu 87 and Asp 88 in the D1 domain of CD4) of Ab 13B8.2 (64), which reorganizes Zap70 outside the rafts and modulates its phosphorylation profile. Concerning the anti-CD4 Ab OKT4, directed against the D4 domain, we were not able, using our experimental procedure, to induce CD4 accumulation/retention into 37°C-extracted Brij 98 DRM upon OKT4 binding without anti-mouse hyper-cross-linking, whereas Fragoso et al (33) showed an increase in the amount of CD4 together with LAT and p56 Lck in 4°C-Triton DRM upon OKT4 cross-linking, followed by anti-mouse hyper-cross-linking.…”

Laboratory control values for CD4 and CD8 T lymphocytes. Implications for HIV-1 diagnosis

“…and HIV-I' tonsil and lymph node samples [ 35 37]. The RFT8 reacts with a p32 (CD8) antigen, and RFT4 reacts with the first domain of CD4 anligen where il binds to the 27, 34 and 55 amino acid residues [38]. RFT4 is similar although not identical to OKT4B and it partially crossblocks Leu-3a.…”

A monoclonal antibody to the gp120-CD4 complex has differential effects on HIV-induced syncytium formation and viral infectivity

“…In addition to acting as a receptor for virus binding, CD4 may also be involved in the subsequent membrane fusion step (Camerini & Seed, 1990;Hasanuma et al, 1992;Poulin et al, 1991 ;Truneh et al, 1991). The CDR3-1ike region of CD4 (amino acids 81-102) (Sattentau et al, 1989) is thought to be involved in HIV-mediated, CD4-dependent membrane fusion, independent of its role in binding to gpl20 (Choe & Sodroski, 1992 1993). In view of the differential effects of several antibodies on these two processes, we have examined the ability of MAb 55 to inhibit HIV-1 infection of the CD4 + T cell lines A3.01, Sup-T1 and H9, as well as its effect on syncytium formation between these three cell lines and chronically HIV-1-infected H9 cells.…”