Microbiology, 2021

CHAPTER 18
Adaptive Specific Host Defenses
Figure 18.1 Polio was once a common disease with potentially serious consequences, including paralysis.
Vaccination has all but eliminated the disease from most countries around the world. An iron-lung ward, such as the
one shown in this 1953 photograph, housed patients paralyzed from polio and unable to breathe for themselves.
Chapter Outline
18.1 Overview of Specific Adaptive Immunity
18.2 Major Histocompatibility Complexes and Antigen-Presenting Cells
18.3 T Lymphocytes and Cellular Immunity
18.4 B Lymphocytes and Humoral Immunity
18.5 Vaccines
INTRODUCTION People living in developed nations and born in the 1960s or later may have difficulty
understanding the once heavy burden of devastating infectious diseases. For example, smallpox, a deadly viral
disease, once destroyed entire civilizations but has since been eradicated. Thanks to the vaccination efforts by
multiple groups, including the World Health Organization, Rotary International, and the United Nations
Children’s Fund (UNICEF), smallpox has not been diagnosed in a patient since 1977. Polio is another excellent
example. This crippling viral disease paralyzed patients, who were often kept alive in “iron lung wards” as
recently as the 1950s (Figure 18.1). Today, vaccination against polio has nearly eradicated the disease.
Vaccines have also reduced the prevalence of once-common infectious diseases such as chickenpox, German
measles, measles, mumps, and whooping cough. The success of these and other vaccines is due to the very
specific and adaptive host defenses that are the focus of this chapter.