Chapter 17 THE IMMUNE SYSTEM AND DISEASE 17.1: Viruses 17.2: Innate Immunity 17.3: Adaptive Immunity 17.4: Disruptions in the Immune System

Viruses are acellular, parasitic entities that are not considered alive because … Viruses infect all forms of organisms

discovered after the development of a porcelain filter used to extract bacteria from liquid tobacco mosaic disease

Virions ~ /1,000,000 mm Virions, single virus particles, are very small, about 20–250 nanometers (1 nanometer = 1/1,000,000 mm). How Big is a...?

electron microscope in the 1940s virion Classification based on: morphology > nucleic acid > molecular analysis

FIGURE 17.6 In influenza virus infection, glycoproteins attach to a host epithelial cell. As a result, the virus is engulfed. RNA and proteins are made and assembled into new virions.

Influenza virus is packaged in a viral envelope, which fuses with the plasma membrane. This way, the virus can exit the host cell without killing it. What advantage does the virus gain by keeping the host cell alive?

Which of the following statements about virus structure is true? a. All viruses are encased in a viral membrane. b. The capsomere is made up of small protein subunits called capsids. c. DNA is the genetic material in all viruses. d. Glycoproteins help the virus attach to the host cell.

FIGURE 17.7 Viruses are the cause of dozens of ailments in humans, ranging from mild illnesses to serious diseases. (credit: modification of work by Mikael Häggström)

Vaccines for Prevention

FIGURE 17.8 There are two main parts to the vertebrate immune system. The innate immune system, which is made up of physical barriers and internal defenses, responds to all pathogens. The adaptive immune system is highly specific.

FIGURE Cells involved in the innate immune response include mast cells, natural killer cells, and white blood cells, such as monocytes, macrophages and neutrophils.