CD19 & CD28

CD19 is a B cell-specific surface molecule that serves as a co-receptor in the B cell receptor (BCR) complex. It is expressed from the early pro-B cell stage through mature B cells but is lost upon plasma cell differentiation. CD19 enhances BCR signaling, lowering the threshold for activation and promoting B cell responses. It plays a critical role in B cell development, activation, and differentiation. CD19 has been utilized as a target for chimeric antigen receptor (CAR) T cell therapies in B cell malignancies, demonstrating its clinical significance.

CD28 is a co-stimulatory receptor found on T cells that plays a key role in T-cell activation and survival. It is a transmembrane protein expressed on naïve and activated T cells, binding to B7-1 (CD80) and B7-2 (CD86) on antigen-presenting cells (APCs). This interaction provides the necessary secondary signal for full T-cell activation, alongside T-cell receptor (TCR) engagement with antigen-presenting major histocompatibility complex (MHC). CD28 signaling promotes cytokine production, T-cell proliferation, and survival. In the absence of CD28 signaling, T cells may become anergic (non-responsive). Because of its role in immune regulation, CD28 is a target for therapeutic interventions in autoimmune diseases, transplantation, and cancer immunotherapy.