CD4 Protein, Human (HEK293, Fc)

The CD4 protein, an integral membrane glycoprotein, assumes a crucial role in immune responses, undertaking diverse functions against both external and internal challenges. In T-cells, its primary function is as a coreceptor for the MHC class II molecule:peptide complex, where class II peptides originate from extracellular proteins, while class I peptides are derived from cytosolic proteins. CD4 interacts concurrently with the T-cell receptor (TCR) and the MHC class II presented by antigen-presenting cells (APCs), leading to the recruitment of the Src kinase LCK to the vicinity of the TCR-CD3 complex. Subsequently, LCK initiates various intracellular signaling pathways by phosphorylating diverse substrates, ultimately resulting in lymphokine production, enhanced motility, adhesion, and the activation of T-helper cells. In other cell types such as macrophages or NK cells, CD4 contributes to differentiation/activation, cytokine expression, and cell migration through a TCR/LCK-independent pathway. Additionally, it plays a pivotal role in the development of T-helper cells in the thymus and triggers the differentiation of monocytes into functional mature macrophages. Notably, CD4 acts as the primary receptor for human immunodeficiency virus-1 (HIV-1), with its down-regulation facilitated by HIV-1 Vpu, and it also serves as a receptor for Human Herpes virus 7/HHV-7.