defense system that has evolved to protect animals from invading pathogenic microorganisms and ancer. It is able to generate an enormous variety of cells and molecules capable of specifically recognizing and eliminat ing an apparently limitless variety of foreign invaders. These cells and molecules act together in a dynamic network whose omplexity rivals that of the nervous system. Functionally, an immune response can be divided into two related activities--recognition and response. Immune

cell receptor when complexed with MHC,are called antigens. The molecular properties of antigens and he way in which these properties ultimately contribute to immune activation are central to our understanding of the mmune system. This chapter describes some of the molecu- Complementarity of Interacting Surfaces of Antibody(left) lar features of antigens recognized by B or T cells. The chap and Antigen(rig ter also explores the contribution made to immunogenicity by the biological system of the host; ultimately the biological system determines whether a molecule that combines with a a Immunogenicity Versus Antigenicity Bor T cells antigen-binding receptor can then induce an im

Kappa Light-Chain Gene Rearrangement the vertebrate immune system is its ability to respond to an apparently limitless array of for eign antigens As immunoglobulin(Ig)sequence data accu- a Genetic Model Compatible with Ig Structure mulated, virtually every antibody molecule studied was found to contain a unique amino acid sequence in its vari a Multigene Organization

possesses a tightly linked cluster of genes. the ma jor products play roles in intercellular recognition and in dis on of vesicular Stomatitis Virus Peptide (top) Class I Molecule H-2K General Organization and Inheritance of the MHC MHC Molecules and Genes that Detailed Genomic Map of MHC Genes Cellular Distribution of MHC Molecules antigens of Regulation of MHC Expression implicated MHC and Immune Responsiveness natural killer

the B-cell rec and diffict Interaction of aB TCR with Class II MHC-Peptide Early Studies of the T-Cell Receptor complex cel aB and yo T-Cell Receptors: Structure and Roles ficity. Sec Organization and Rearrangement of TCR Genes gen alone by the major histo T-Cell Receptor Complex: TCR-CD3 erty precludes pur

production of plasma cells and memory B cells can be divided into three broad stages: generation of mature, immunocompetent B cells(maturation), activa- Initial Contact between b and T cells tion of mature B cells when they interact with antigen, and differentiation of activated B cells into plasma cells and memory B cells. In many vertebrates, ng humans B-Cell maturation and mice, the bone marrow generates B cells. This process

of the humoral branch of the immune system Research on complement began in the 1890s, when Jules bordet at the institut pasteur in paris showed that sheep antiserum to the bacterium vibrio cholerae caused lysis of the bacteria and that heating the antiserum destroyed its bacteriolytic activity. Surprisingly, the ability to lyse the bacteria was restored to the heated serum by adding fresh serum that contained no antibodies directed a The Functions of Complement

part of the body to another. This is espe- ially true of lymphocytes, which circulate ly in the blood and lymph and, in common with at sites o Lymphocytes Attached to the Surface of a High-Endothelial Venule sLymphocyte Recirculation Cell-Adhesion Molecules Neutrophil Extravasation Lymphocyte Extravasation Chemokines-Key Mediators of Inflammation Other Mediators of Inflammation The Inflammatory Process

susceptible host, a series of coordinated events must rcumvent both innate and adaptive immunity. One of the first and most important features of host innate immunity is the barrier provided by the epithelial surfaces of the skin and the lining of the gut. The difficulty of penetrat- ing these epithelial barriers ensures that most pathogens never gain productive entry into the host. In addition to pro viding a physical barrier to infection, the epithelia also pro duce chemicals that are useful in

lure can have dire consequences. Nude Mouse (nu/nu) elf and begins to attack hich is Primary Immunodeficiencies AIDS and Other Acquired or Secondary Immunodeficiencies at birth differentiated from immunodeficiencies in which the non- specific mediators of innate immunity, such as phagocytes or ed. Immunodeficiencies are conve- by the type or the developmental stage of overall cellular de g the locations of prevennon stra