Cluster of Differentiation 4 (CD4) is a membrane glycoprotein of the immunoglobulin superfamily that functions as a co-receptor of the T-cell receptor (TCR), facilitating antigen recognition through interaction with major histocompatibility complex (MHC) class II molecules on antigen-presenting cells. This interaction stabilizes the TCR–MHC complex and enhances intracellular signaling, promoting T-cell activation and adaptive immune responses. CD4 is primarily expressed on CD4⁺ helper T lymphocytes and at lower levels on monocytes, macrophages, and dendritic cells, making it a key immunophenotypic marker of immune cell subsets.

Biological Significance of Cluster of Differentiation 4 (CD4)

• Binds MHC class II molecules to enable efficient antigen recognition.
• Activates CD4⁺ T-helper lymphocytes through TCR-mediated signaling.
• Cytoplasmic domain associates with Lck kinase, amplifying TCR signaling and regulating cytokine production.
• Defines T-helper cell lineages that orchestrate immune responses by regulating B-cell activation, macrophage function, and cytotoxic T-cell responses.
• Enriched in paracortical/interfollicular zones of lymphoid tissues, reflecting a key role in adaptive immune regulation.

Diagnostic Utility of CD4 in Hematopathology

• Identifies T-helper lymphocyte populations in tissue sections.
• Assesses the immune microenvironment in lymphoid tissues.
• Supports classification of hematolymphoid neoplasms, including several mature T-cell lymphomas that frequently show CD4 expression.
• Aids differentiation among T-cell, NK-cell, and histiocytic proliferations.
• Evaluates T-cell–rich inflammatory or neoplastic infiltrates for accurate lymphoid lesion interpretation.

Key Features of CD4 CE/IVD Antibodies for IHC

• Validated for diagnostic IHC in formalin-fixed, paraffin-embedded (FFPE) tissue.
• High specificity for CD4-expressing immune cells.
• Membranous staining pattern enables clear visualization of CD4-positive lymphocytes.
• Suitable for tumor microenvironment assessment and lymphoid lineage determination.
• Optimized for routine pathology platforms and standardized CE/IVD protocols.