T cell receptor
The T cell receptors are found on T cells (T lymphocytes). T cells are involved in the cell-mediated response. T cell receptors are dimers. Most commonly T cell receptors consist of two glycosylated disulphide-linked alpha and beta chains. A very small amount is made of a gamma and delta units. The chains are associated with CD3 proteins to make T cell receptors CD3 at the cell surface membrane. Gamma and alpha chains are also associated with CD3 proteins. T cells are able to distinguish antigens which have been processed into surface peptides and bound to MHCs.
T helper cells (also called as CD4+ when mature) recognise peptide antigens which are bound to MHC class II molecules on dendrite cells, macrophages and B cells. There are 2 types of T helper cells; Th1 cells destroy virus-infected cells and stimulate B-cell activation and Th2 which assist B-cells to develop into memory cells and plasma cells which manufacture antibodies.