CD8A

CD8A Full Name

CD8a molecule

CD8A Introduction

CD8A encodes the CD8 alpha chain, a transmembrane glycoprotein that serves as the definitive surface marker for cytotoxic T lymphocytes. As an essential component of the CD8 coreceptor complex, CD8A plays a fundamental role in the adaptive immune system by enabling T cells to recognize and eliminate virus-infected cells, tumor cells, and allogeneic grafts. The protein functions primarily as a coreceptor with the T-cell receptor (TCR) to recognize antigens displayed by antigen-presenting cells in the context of major histocompatibility complex (MHC) class I molecules. Beyond its immunological functions, CD8A has emerged as a clinically significant biomarker for cancer prognosis, immunotherapy response prediction, and genetic disorders of immunity.

Figure 1. Strcuture of CD8A protein.

Genomic Characteristics and Protein Structure
The CD8A gene is located on human chromosome 2 at position 2p11.2, while its murine ortholog (Cd8a) resides on chromosome 6. The gene produces multiple transcript variants encoding different protein isoforms, with the major isoforms differing by the presence or absence of a transmembrane domain—resulting in both membrane-anchored and secreted protein forms.
The CD8 alpha chain protein comprises several distinct structural regions essential for its function. These include an N-terminal signal peptide, an extracellular immunoglobulin V-set domain that mediates MHC class I binding, a hinge region, a transmembrane domain, and a cytoplasmic tail. The immunoglobulin V-set domain shares significant homology with immunoglobulin variable light chains and contains complementarity-determining regions that facilitate antigen recognition. The CD8 coreceptor functions either as a homodimer composed of two alpha chains (CD8αα) or as a heterodimer composed of one alpha and one beta chain (CD8αβ). The CD8αβ heterodimer is the predominant form expressed on mature cytotoxic T lymphocytes, while CD8αα homodimers are found on specific T-cell subsets and innate lymphoid cells.

Regulation of CD8A Expression
CD8A expression is tightly regulated at multiple levels during T-cell development and differentiation. Epigenetic mechanisms, particularly DNA methylation at CpG sites within the Cd8a locus, play a crucial role in establishing and maintaining appropriate expression patterns. During thymic development, progressive demethylation of specific regions including the E8V enhancer, distal promoter, transcription start site, and intragenic regions correlates with the initiation and maintenance of CD8 expression. In peripheral CD8+ T cells, cytokine signals modulate CD8A expression levels. Interleukin-2, IL-4, IL-7, and IL-15 increase CD8 levels on naive T cells by enhancing Cd8a transcription in the absence of TCR stimulation. Conversely, exposure to IL-4 during activation causes sustained downregulation of Cd8a mRNA and surface CD8, accompanied by reduced antigen sensitivity and acquisition of type 2 cytokine profiles—effects that are antagonized by interferon-γ. Importantly, CD8A expression exhibits epigenetic plasticity even in differentiated effector T cells. Studies have shown that CD8low type 2-polarized cells can respond to IFN-γ by re-expressing CD8 and adopting a type 1 cytokine profile, associated with partial demethylation of the Cd8a locus. This persistent capacity for epigenetic reprogramming enables heritable tuning of antigen sensitivity in parallel with changes in cytokine balance.

Alternate Names for CD8A

CD8A; CD8a molecule; T-cell surface glycoprotein CD8 alpha chain; CD8 antigen, alpha polypeptide (p32);