Immunobiological and immunochemical aspects of the T-200 family of glycoproteins.

We present some new structural and functional data on the family of high mol. wt glycoproteins of human hematopoietic cells which strongly suggests they play a role proximate to certain Ca2+-dependent events. Structural data on this complex are presented which describe elements of its tertiary structure and associations between the different glycoproteins in the plasma membrane. The mol. wt profile of the T-200 structures on highly enriched natural killer (NK) cells is used to support an argument for a T-cell vs a myeloid nature for NK cells. Furthermore, certain murine monoclonal antibodies directed to a particular epitope of T-200 on NK cells are shown to block cytolysis. The specificity of this blockade strongly suggests that T-200 may be an NK receptor. A mapping of this effect has allowed us to define a new stage of the lytic cycle, termed "triggering". This very rapid event occurs subsequent to conjugation between the NK and the target cell, and prior to the Ca2+-dependent second-phase programming for lysis. A close association between "triggering", as defined by antibodies to T-200, and Ca2+-dependent stimulus-secretion events support the concept of T-200 as a receptor structure.