8536d_ch03_057-075 8/7/02 9: 18 AM Page 57 mac79 Mac 79: 45_BW: Goasby et al./ Immunology 5e Ant gens chapter 3 UBSTANCES THAT CAN BE RECOGNIZED BY THE or cell receptor when complexed with MHC,are called antigens. The molecular properties of antigens and ribute to to our understanding of th 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(right) 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 m Immunogenicity Versus Antigenicity B or T cells antigen-binding receptor can then induce an im a Factors That Influence Immunogenicity mune response. Fundamental differences in the way B and T determine which molecular features of an antigen are recognized by each branch of the a Haptens and the Study of Antigenicity immune system. These differences are also examined in this chapter a Pattern-Recognition Receptors Immunogenicity versus Antigenicity Immunogenicity and antigenicity are related but distinct Factors That Influer munologic properties that sometimes are confused mmunogenicifyhce munogenicity is the ability to induce a humoral and/or mediated immune response To protect against infectious disease, the immune system must be able to recognize bacteria, bacterial products, fungi B cells antigen effector B cells memory B cells parasites, and viruses as immunogens. In fact, the immune system actually recognizes particular macromolecules of an (plasma cells) infectious agent, generally either proteins or polysaccharides. T cells antigen effector T cells memory T cells Proteins are the most potent immunogens, with polysaccha- (e. g, CTLS, THS an infectious agent generally do not serve as immunogens unless they are complexed with proteins or polysaccharides Although a substance that induces a specific immune re- Immunologists tend to use proteins or polysaccharides as sponse is usually called an antigen, it is more appropriately immunogens in most experimental studies of humoral im- munity(Table 3-1). For cell-mediated immunity, only pro Antigenicity is the ability to combine specifically with teins and some lipids and glycolipids serve as immunogens the final products of the above responses(i.e, antibodies These molecules are not recognized directly. Proteins must and/or cell-surface receptors). Although all molecules that first be processed into small peptides and then presented to- have the property of immunogenicity also have the property gether with MHC molecules on the membrane of a cell be- of antigenicity, the reverse is not true. Some small molecules, fore they can be recognized as immunogens. Recent work called haptens, are antigenic but incapable, by themselves, of shows that those lipids and glycolipids that can elicit cell- inducing a specific immune response. In other words, they mediated immunity must also be combined with MHC-like membrane molecules called CDI(see Chapter 8)Factors That Influence Immunogenicity To protect against infectious disease, the immune system must be able to recognize bacteria, bacterial products, fungi, parasites, and viruses as immunogens. In fact, the immune system actually recognizes particular macromolecules of an infectious agent, generally either proteins or polysaccharides. Proteins are the most potent immunogens, with polysaccha￾rides ranking second. In contrast, lipids and nucleic acids of an infectious agent generally do not serve as immunogens unless they are complexed with proteins or polysaccharides. Immunologists tend to use proteins or polysaccharides as immunogens in most experimental studies of humoral im￾munity (Table 3-1). For cell-mediated immunity, only pro￾teins and some lipids and glycolipids serve as immunogens. These molecules are not recognized directly. Proteins must first be processed into small peptides and then presented to￾gether with MHC molecules on the membrane of a cell be￾fore they can be recognized as immunogens. Recent work shows that those lipids and glycolipids that can elicit cell￾mediated immunity must also be combined with MHC-like membrane molecules called CD1 (see Chapter 8). chapter 3 ■ Immunogenicity Versus Antigenicity ■ Factors That Influence Immunogenicity ■ Epitopes ■ Haptens and the Study of Antigenicity ■ Pattern-Recognition Receptors Antigens S       immunoglobulin receptor of B cells, or by the T￾cell receptor when complexed with MHC, are called antigens. The molecular properties of antigens and the way in which these properties ultimately contribute to immune activation are central to our understanding of the immune system. This chapter describes some of the molecu￾lar features of antigens recognized by B or T cells. The chap￾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 B or T cell’s antigen-binding receptor can then induce an im￾mune response. Fundamental differences in the way B and T lymphocytes recognize antigen determine which molecular features of an antigen are recognized by each branch of the immune system. These differences are also examined in this chapter. Immunogenicity Versus Antigenicity Immunogenicity and antigenicity are related but distinct immunologic properties that sometimes are confused. Im￾munogenicity is the ability to induce a humoral and/or cell￾mediated immune response: B cells antigen n effector B cells + memory B cells g (plasma cells) T cells antigen n effector T cells + memory T cells g (e.g., CTLs, THs) Although a substance that induces a specific immune re￾sponse is usually called an antigen, it is more appropriately called an immunogen. Antigenicity is the ability to combine specifically with the final products of the above responses (i.e., antibodies and/or cell-surface receptors). Although all molecules that have the property of immunogenicity also have the property of antigenicity, the reverse is not true. Some small molecules, called haptens, are antigenic but incapable, by themselves, of inducing a specific immune response. In other words, they lack immunogenicity. Complementarity of Interacting Surfaces of Antibody (left) and Antigen (right) 8536d_ch03_057-075 8/7/02 9:18 AM Page 57 mac79 Mac 79:45_BW:Goldsby et al. / Immunology 5e: