Bacterial Infections

Immunity to bacterial infections is achieved by means of antibody unless the bacterium is capable of intracellular growth, in which case delayed-type hypersensitivity has an important role. Bacteria enter the body either through a number of natural routes (e.g., the respiratory tract, the gastrointestinal tract, and the genitourinary tract) or through normally inaccessible routes opened up by breaks in mucous membranes or skin. Depending on the number of organisms

Tip/interface

Binding cleft

Loop

Hinge

ß pleated sheet

Tip/interface

Binding cleft

Loop

Hinge

ß pleated sheet

Bacterial Antigenic Variation

a helix

Structure of hemagglutinin molecule. Sialic acid on host cells interacts with the binding cleft, which is bounded by regions—designated the loop and tip/interface—where antigenic drift is prevalent (blue areas). Antibodies to these regions are important in blocking viral infections. Continual changes in amino acid residues in these regions allow the influenza virus to evade the antibody response. Small red dots represent residues that exhibit a high degree of variation among virus strains. [Adapted from D. C. Wiley et al, 1981, Nature 289:373]

a helix

FIGURE 17-7

Structure of hemagglutinin molecule. Sialic acid on host cells interacts with the binding cleft, which is bounded by regions—designated the loop and tip/interface—where antigenic drift is prevalent (blue areas). Antibodies to these regions are important in blocking viral infections. Continual changes in amino acid residues in these regions allow the influenza virus to evade the antibody response. Small red dots represent residues that exhibit a high degree of variation among virus strains. [Adapted from D. C. Wiley et al, 1981, Nature 289:373]

Go to www.whfreeman.com/immunology Molecular Visualization

Viral Antigens See Introduction and Flu Virus Hemagglutinin.

entering and their virulence, different levels of host defense are enlisted. If the inoculum size and the virulence are both low, then localized tissue phagocytes may be able to eliminate the bacteria with an innate, nonspecific defense. Larger inoculums or organisms with greater virulence tend to induce an adaptive, specific immune response.

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