Caveolin-1: The Unnoticed Player in TCR and BCR Signaling.

ABSTRACT

T and B lymphocytes are key players of the adaptive immune system. They recognize pathogenic cues via the T cell antigen receptor (TCR) and the B cell antigen receptor (BCR) to get activated and execute their protective function. TCR and BCR signaling are initiated at the plasma membrane and subsequently propagated into the cell, ultimately leading to cell activation and a protective immune response. However, inappropriate activation of T and B cells can be detrimental to the host resulting in autoimmune disorders, immunodeficiencies, and cancer. The TCR and BCR are located at the plasma membrane, which composition is highly heterogenic. Membrane compartmentalization based on specific lipid-lipid and protein-lipid interactions has raised the interest of the scientific community, converting the plasma membrane into an active player in the initiation of signaling and adding an additional layer of regulation to our current understanding of the functioning of antigen receptors. Caveolin-1 is an integral membrane protein and a crucial component of caveolae. It has been long thought that lymphocytes lack Caveolin-1 expression, due to the absence of detectable caveolae in lymphocytes and the failure to detect Caveolin-1 in T and B cell lines. However, Caveolin-1 is expressed at low levels in primary lymphocytes, and recent studies have shown the importance of Caveolin-1 for the basal membrane organization of the BCR and the TCR as well as their reorganization upon activation. Here, we review our current understanding of the initial signaling events of TCR and BCR activation with respect to receptor compartmentalization on the plasma membrane and with special emphasis on the previously unnoticed role of Caveolin-1.