The T cell receptor was very difficult to get a handle on and wasn't cloned until 1984. History You'll recall that von Behring and Kitasato had identified an antitoxin circulating in serum that protected animals from challenge with diphtheria. They collected the immune serum and divided it into two aliquots. I.e. the antigen reactive material was a g -globulin. AND Mike Potter found that mineral oil delivered I.P. into mice would induce B cell tumors.
Heavy chain has one V region and three or more C-regions.
Kabat speculated that the hypervariable regions were the sources of antigen specificity and diversity. It is important to remember that the structure of the BCR is the same as the structure of the antibody - the only difference is that it is membrane bound.