immunology, refers to the act of transferring cells, tissues, or organs from one site to another. The desire to accomplish transplants stems from the realization that many diseases can be cured by implantation of a healthy organ, tissue, or cells(a graft)from one individual (the donor)to another in need of the transplant(the recipient or

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

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

ne system assume different roles in pro- the host. The effectors of the humoral molecules f cells Big CTL Attacks Little Tumor Cell Effector Responses General Properties of Effector Cells Cytotoxic T Cells Natural Killer Cells Antibody-Dependent- Cell-Mediated- Cytotoxicity Experimental Assessment of Cell-Mediated Cytotoxicity

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

recognition by most T cells from recognition by B iction. In most cases, both th maturati vation of ma the involver diversity o CD4\ and CD class I MHC Activat Engagement of TcR by Peptide: MHC Initiates interaction of th n antigenic Signal Transduction tide displayed though the sp

lecular association similar to an enzyme-substrate interaction, with an important distinction: it does not lead to an irreversible chemical alteration in either the antibody or the antigen. The association between an anti Fluorescent Antibody Staining Reveals Intracellular body and an antigen involves various noncovalent interac- tions between the antigenic determinant, or epitope, of the ntigen and the variable-region(vH/Vi) domain of the an- a Strength of Antigen-Antibody Interactions tibody molecule, particularly the hypervariable regions

present on the B-cell membrane and secreted by plasma cells. Membrane-bound antibody con- fers antigenic specificity on B cells; antigen-specific prolifer- ation of B-cell clones is elicted by the interaction of membrane antibody with antigen Secreted antibodies ci culate in the blood, where they serve as the effectors of hu- moral immunity by searching out and neutralizing antigens or marking them for elimination. All antibodies share struc

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

A conditional sentence (or \conditional\ for short) is commonly composed of two parts: conditional clause main clause. Despite the many possible sequences of verb forms in conditionals, the following four types represent perhaps the commonest and the most useful ones: