CD4 serves as the primary receptor for HIV-1 entry through its interaction with the viral envelope glycoprotein gp120. It is also a target of autoantibodies reported in some individuals with HIV-1 infection. Studying these interactions requires recombinant CD4 that retains relevant antibody-binding epitopes and the ability to move the body engage gp120.
Conigen’s soluble CD4 dimer supports both applications, with validation spanning antibody recognition, specific gp120 binding, pseudovirus neutralization, and anti-CD4 autoantibody detection in patient-derived samples.
Recombinant protein quality extends beyond purity. For CD4 research, the reagent must also present relevant epitopes and maintain ligand-binding activity.
Conigen’s CD4 dimer demonstrated binding to the anti-CD4 monoclonal antibody keliximab, with an ELISA EC₅₀ of approximately 6.8 ng/mL. It also bound wild-type HIV-1 gp120, while binding was diminished for the D368R mutant, which disrupts the canonical CD4-binding site.
These complementary assays support antibody recognition and engagement through the expected CD4–gp120 interface. Non-reducing SDS-PAGE further showed a single predominant band at the expected molecular weight, supporting the preparation’s purity.
Functional Activity in HIV-1 Neutralization Assays
Soluble CD4 provides a tool for investigating receptor-dependent viral entry. By engaging the viral envelope, it can inhibit infection in pseudovirus assays.
Conigen’s CD4 dimer demonstrated neutralization activity against four tested HIV-1 tier 2 strains. Pseudoviruses were pre-incubated with serial dilutions of the CD4 dimer or a CD4-Ig comparator before addition to TZM-bl reporter cells. Infection was quantified using luciferase activity.
Across all four strains, the CD4 dimer achieved 50% inhibition at lower concentrations than the comparator. For Q23.17, Yu2, and JR-FL, the CD4 dimer demonstrated approximately 11–15-fold greater potency based on the reported mass concentrations. These results establish functional activity in the tested pseudovirus systems and support its use in HIV-1 research.
Anti-CD4 Antibody Detection in Patient-Derived Samples
Anti-CD4 autoantibodies have been investigated for decades, with reports in HIV infection dating back to the late 1980s. Subsequent studies have examined their binding specificity, recognition of cell-surface CD4, and potential effects on T-cell function. Some studies have associated these antibodies with impaired immune recovery in people with HIV, although findings vary across patient populations and experimental systems.
Interest in anti-CD4 antibodies also extends beyond HIV. Studies in systemic lupus erythematosus (SLE) have identified antibodies that recognize native and recombinant CD4. Experimental work with purified SLE-derived antibodies has demonstrated effects on T-cell proliferation, providing a rationale for investigating CD4-reactive antibodies in autoimmune disease. These findings also underscore the importance of evaluating antibody binding and biological activity separately.
Antigen format can influence which antibody reactivities a screening assay detects. Published epitope-mapping studies have identified anti-CD4 autoantibody recognition within the D3–D4 region, highlighting the value of including all four extracellular domains. Conigen’s CD4 dimer presents two complete D1–D4 ectodomains, providing broad domain coverage and the potential for multivalent antibody interactions.
In an ELISA comparison, purified IgG from individuals with HIV-1 was screened using either Conigen’s CD4 dimer or a commercial soluble CD4 monomer as the capture antigen under identical assay conditions. The CD4 dimer detected measurable anti-CD4 reactivity in two patient samples. This reactivity was reproducible and above background thresholds established using healthy donor controls. The monomeric comparator showed no detectable reactivity across the samples tested.
These preliminary findings support further evaluation of the CD4 dimer for anti-CD4 antibody screening and characterization. Differences in epitope accessibility, stability, or avidity may contribute to the observed detection, although the experiments do not establish the underlying mechanism.
Conigen CD4 Dimer Characterization and Quality Testing
Recombinant protein quality depends on both purity and performance in the intended application. Conigen’s CD4 dimer is characterized through complementary assays that evaluate purity, antibody recognition, specific ligand binding, and biological activity. Together, these assessments support its use in CD4 research, from studying HIV-1 interactions to detecting anti-CD4 antibodies.
To learn how Conigen’s CD4 dimer could support your research, contact our team to discuss your application or explore collaboration opportunities with our scientists.
For research use only. Not for diagnostic or therapeutic use.
A: The key is whether a protein retains the binding properties or biological activity your experiment requires. Look for validation that matches your intended application—for example, recognition by a relevant antibody, specific ligand binding, or activity in a functional assay.
Our CD4 application note illustrates this approach by combining antibody binding, gp120 recognition, and HIV-1 pseudovirus neutralization assays. It also shows that reagent format can affect results: the CD4 dimer detected autoantibody reactivity in two patient samples that was undetectable with a monomeric comparator under the tested conditions.
When selecting a reagent, ask: Has it been shown to perform the interaction my assay depends on?
Featured Soluble Proteins Across T Cell Targets
The Conigen Difference
Bioactive, native-like recombinant T cell surface proteins designed to support antibody screening, receptor–ligand binding studies, and therapeutic discovery targeting T cell recognition, activation, and immune regulation.
Introduction CD4 is a cell-surface glycoprotein expressed primarily on T helper lymphocytes and plays a central role in adaptive immune regulation. Beyond its physiological function,
Poster Abstract The CD4 molecule on the T-cell surface can present as monomer and dimer forms. Dimeric CD4 can be important for T-cell activation. As
