The humoral response of the immune system to a foreign antigen usually requires the recognition of two antigenic determinants. The one, called the carrier, is recognized by T-Iymphocytes, the other, called the hapten, by B-Iympho cytes. As a consequence, T - and B-Iymphocytes proliferate, B-Iymphocytes produce hapten-specific antibodies, and the system develops memory to the antigens. It was long thought that antigens would form a bridge to mediate the cooperation of T - and B-Iymphocytes. However, it now appears that antigens are broken down to fragments which then act as carrier determinants for T -lymphocytes. The cells which originally process antigen are called an tigen-presenting cells. They have phagocytic properties. They can take up and degrade antigens, in the case of pro teins to peptides. The peptides of protein antigens reappear on the surface of the antigen-presenting cells, where they must become associated with membrane proteins encoded by genes of the major histocompatibility complex (MHC) in order to be recognized by T-Iymphocytes. To activate helper T-Iym phocytes which cooperate in antibody responses, MHC class II molecules have to be expressed on the surface of the antigen-presenting cells. Once T -lymphocytes have be come activated, they are ready to cooperate with B cells.

Inhalt
Peptides as Immunogens: Prospects for Synthetic Vaccines. With 1 Figure.- Molecular Features of Class II MHC-Restricted T-Cell Recognition of Protein and Peptide Antigens: The Importance of Amphipathic Structures. With 1 Figure.- Peptides as Probes to Study Moleeular Mimicry and Virus-Induced Autoimmunity. With 2 Figures.- The Use of Peptides in Studying Mechanisms of Immune Tolerance. With 4 Figures.- Immune Response to Synthetic Herpes Simplex Virus Peptides: The Feasibility of a Synthetic Vaccine. With 10 Figures.- Antigen Presentation by B Lymphocytes: A Critical Step in T-B Collaboration. With 3 Figures.- The Value of Synthetic Peptides as Vaccines for Eliciting T-Cell Immunity.- Indexed in Current Contents.