How T cells talk to target cells

T cell defects are very often involved in haematological diseases and occur even more frequently as a consequence of our therapeutic interventions. T cells play a central role in the immune defence of the organism. To perform this function, they move around the body to achieve a particular stage of development and in search for antigenic insult. In the course of this, they have to communicate and cooperate with various cells. T cells carry a high number of structurally and functionally defined and even more as yet undefined surface structures. The variability and functional pleitropism of these molecules and as a consequence that of their interactions with surface structures of other cells is infinite. This paper will be limited to discuss briefly the following subjects: the presentation of antigens to T cells, structure and function of the T cell receptor (TCR) and its interactions with the antigen, presenting major histocompatibility complex (MHC) molecule, accessory molecules and other modulating surface structures, the role of carbohydrates, pitfalls of inferences on interacting cell surface structures.