When creating a new edition of a textbook on primary antigen recognition, there is a tendency to integrate new aspects into the fundamentals with a detailed discussion of the structure of the first edition, without considering the T-cell. The subsequent chapter addresses the evidence of this recognition process and the necessary changes. However, my understanding of the laboratory applications based on this has changed so significantly in the 17 years since the first edition was published that a fundamental redesign of the structure of this book was inevitable. The next four chapters deal with the immune response in relation to antigen recognition. Chapter 6 illustrates the early processes involved in lymphocyte activation.