We know that there are at least three cell types required for cell receptors, namely the T-cell, B-cell and macrophage. Different classes of cells can readily be distinguished, however, by virtue of the fact that they express unique combinations of molecules in their membranes. Our knowledge of the different cell types involved in cell receptors is a direct result of the development of reagents to distinguish these various cells by their cell surface markers. We will see that such markers include molecules distinguished either by antibodies directed against them, or else by their ability to bind various other molecules or cells.
The T-cell antigen receptor (TCR) is the principle defining marker of all T-cells. Also associated with the TCR is a complex of proteins known as CD3, which participate in the transduction of an intracellular signal following TCR binding to its cognate MHC/antigen complex.
The B cell antigen receptor (BCR) is composed of membrane immunoglobulin (mIg) molecules and associated CD79a / CD79bbheterodimers. The mIg subunits bind antigen, resulting in receptor aggregation, while the CD79a/CD79b subunits transduce signals to the cell interior. These receptors such as CD19, CD22, CD32, CD45, and some other CD antigens.