body. These organs can be classified functionally nto two main groups. The primary lymphoid organs provide appropriate microenvironments for the development and maturation of lymphocytes. The secondary lymphoid organs rap antigen from defined tissues or vascular spaces and are sites where mature lymphocytes can interact effectively with that antigen. Blood vessels and lymphatic systems connect these organs, uniting them into a functional whole Carried within the blood and lymph and populating the Macrophage Interacting with

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

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

that peptides derived from the antigen be displayed within the cleft of an MHC peptide-Mhcthe m ormation of the Antigen Processing for Presentation by Class I MHC Molecules Self-MHC Restriction of T Cells Class tides that Role of Antigen-Presenting Cells Evidence for Two Processing and Presentation Pathways

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

response involves lymphoid cells, inflammatory cells, and hematopoietic cells. The complex inter- lls are mediated by a group of pro- les to denote their role in secreted by body in activity of cyto- Class I Cytokine Receptors receptors,signal ptors, the role of cytokine Properties of Cytokines

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

effector molecules that act to remove antigen b ren various mechanisms described in previous chap es antigen without A Second Exposure to Poison Oak May Result in Delayed-Type Hypersensitivity Gell and Coombs Classification IgE-Mediated (Type I) Hypersensitivity Antibody-Mediated Cytotoxic(Type) Hypersensitivity aImmune Complex-Mediated (Type Ill) Hypersensitivity

the early vaccination trials of Edward Jenner and oneering efforts, vac nce of diseases such ng cougl Vaccination with DN A Active and Passive Immunization Designing Vaccines for Active Immunization mWhole-Organism Vaccines Purified Macromolecules as Vaccines Recombinant-Vector Vaccines DNA Vaccines Multivalent Subunit Vaccines mmon usage. Experience has shown that not every vaccine

realized that the immune system could go awry and, instead of reacting against foreign antigens, could focus its attack on self-antigens. He termed this con- dition\horror autotoxicus \We now understand that while mechanisms of self-tolerance normally protect an individual from potentially self-reactive lymphocytes, there are failures They result in an inappropriate response of the immune system against self-components termed autoimmunity In the 1960s, it was believed that all self-reactive lymphocytes