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Updated: Aug 11, 2026
Visualizing Antigen Specific CD4+ T Cells using MHC Class II Tetramers
Published on: March 6, 2009
Direct evidence for native CD4 oligomers in lymphoid and monocytoid cells
G W Lynch1, A J Sloane, V Raso
1Centre for Virus Research, Westmead Institutes of Health Research, Westmead Hospital and University of Sydney, Sydney, Australia. GARRYL@Westgate.WH.USYD.EDU.AU
Insights
The CD4 protein, found on T lymphocytes and monocytes, exists in various forms, including monomers, dimers, and tetramers, challenging its traditional monomeric view. These quaternary structures are influenced by thiol interactions and cell activation.
Area of Science:
- Immunology
- Cell Biology
- Protein Biochemistry
Background:
- CD4 is a cell surface glycoprotein crucial for T cell and monocyte function.
- It is traditionally viewed as a monomer, despite early structural models suggesting a homodimer.
Purpose of the Study:
- To investigate the quaternary structure of native CD4 in lymphoid and monocytoid cells.
- To identify factors influencing CD4 oligomerization.
Main Methods:
- Immunoprecipitation and immunoblotting using reducing and alkylating agents.
- MALDI-Tof mass fingerprinting of purified CD4 oligomers.
- Cell surface labeling with thiol-reactive reagents.
- Analysis of recombinant CD4 (rCD4) self-association.
Main Results:
- Native CD4 exists as monomers (55 kDa) and dimers (110 kDa) in lymphoid and monocytoid cells.
- Full reduction yields only the monomeric form, indicating disulfide bonds in dimers.
- CD4 dimerization and tetramerization are enhanced by specific cell treatments and involve thiol exchange interactions, likely in the D4 domain.
- PMA activation of THP-1 cells increases CD4 dimer expression.
Conclusions:
- CD4 exhibits diverse quaternary structures (monomers, homodimers, tetramers) in T lymphocytes and monocytes/macrophages.
- Thiol-dependent interactions play a significant role in CD4 oligomerization.
- These findings necessitate a re-evaluation of CD4's structural and functional properties.
Abstract:
CD4 is expressed by T lymphocytes and monocytes and is generally considered a monomer even though its structure was originally modelled on the REI Bence-Jones homodimer. However, native CD4 was demonstrated as both monomer and dimers of 55 and 110 kDa in lymphoid and monocytoid cells by immunoprecipitation and immunoblotting after solubilization with alkylating (iodoacetamide) or reducing (dithiothreitol, 2-mercaptoethanol) reagents. Full reduction yielded only the 55-kDa monomeric form. Purified CD4 oligomers from CEM-T4 cells were also resolved as homodimers by MALDI-Tof mass fingerprinting after tryptic digestion. Cell treatment with the membrane impermeable, free-thiol reactive, 5,5'-dithiobis-2-nitrobenzoic acid enhanced cell surface CD4 dimers and tetramers. The interaction sites producing dimerization were probably in the D4 domain as OKT4 inhibited self association of recombinant CD4 (rCD4). Oligomerization of rCD4 by glutathione and thioredoxin indicates that thiol exchange interactions were responsible. Enhanced CD4 dimer expression was also observed after PMA (20 ng/ml) activation of THP-1 cells. These findings demonstrate that different quaternary forms of CD4 such as monomers, homodimers and tetramers are expressed by T lymphocytes and monocytes/macrophages.
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