ABSTRACT
In the preceding two chapters, we saw that the host defense relies on two mechanisms to survive against relentless pathogenic assault. The innate (nonspecific) immune response protects against most of these infections, and the adaptive (specific) immune response is mobilized against pathogens that persist despite the innate defenses. Recall that both of these systems are elegantly designed to deal with keeping the body safe and that a host with a deficient immune system (an immunocompromised host) is more susceptible to infection. In this chapter, we first examine some of the ways in which host defense can be lost: infection with HIV, infection by other pathogens, and genetic abnorm alities. In the second part of the chapter, we look at what happens when the immune system turns on the host in the form of autoimmunity and hypersensitivity reactions.
