CD4 Extracellular Domain (human, recombinant)

CD4 is a type I transmembrane glycoprotein that functions as a T cell receptor (TCR) co-receptor.¹ It exists as a single polypeptide chain composed of four extracellular immunoglobulin-like (Ig-like) domains that interact with MHC class II molecules, a transmembrane domain, and a cytoplasmic tail that associates with the tyrosine kinase LCK and mediates signal transduction to the TCR, which is essential for T cell activation.² It is expressed on the surface of, and used as a marker for, T cells, and its expression is used to characterize the development stage of thymocytes. Upon binding to antigen-displaying MHC class II molecules expressed by antigen-presenting cells (APCs), naïve CD4⁺ T cells differentiate and proliferate in a cytokine-dependent manner into a variety of T helper (Th) cell subsets, including Th1, Th2, and Th17 cells, which enhance and direct innate and adaptive immune cell responses to numerous pathogens and have additional roles in cancer, asthma and allergy, and autoimmunity.^3,4 CD4 is also the receptor for HIV attachment and entry into cells, resulting in depletion of CD4⁺ cells in patients infected with HIV.^5,6 Cayman's CD4 Extracellular Domain (human, recombinant) protein can be used for cell-based assay applications. This protein is a disulfide-linked homodimer. The reduced monomer, comprised of CD4 (amino acids 26-390) fused to human IgG1 Fc at its C-terminus, consists of 603 amino acids, has a calculated molecular weight of 67.4 kDa, and a predicted N-terminus of Lys26 after signal peptide cleavage.

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1. Wittlich, M., Koenig, B.W., Hoffmann, S., et al. Structural characterization of the transmembrane and cytoplasmic domains of human CD4. Biochim. Biophys. Acta 1768(12), 2949-2960 (2007).

2. Mak, T.W., and Saunders, M.E. The T cell receptor: Structure of its proteins and genes. The immune response: Basic and clinical principles 311-340 (2006).

3. Nguyen, Q.P., Deng, T.Z., Witherden, D.A., et al. Origins of CD4⁺ circulating and tissue-resident memory T-cells. Immunology 157(1), 3-12 (2019).

4. Zhu, J., and Paul, W.E. CD4 T cells: Fates, functions, and faults. Blood 112(5), 1557-1569 (2008).

5. Wilen, C.B., Tilton, J.C., and Doms, R.W. HIV: Cell binding and entry. Cold Spring Harb. Perspect. Med. 2(8), a006866 (2012).

6. Vijayan, K.K.V., Karthigeyan, K.P., Tripathi, S.P., et al. Pathophysiology of CD4⁺ T-cell depletion in HIV-1 and HIV-2 infections. Front. Immunol. 8, 580 (2017).