Chapter 1 - Immunology of Ascaris and Immunomodulation

Abstract

Natural infections with Ascaris lumbricoides and A. suum of pigs and humans, respectively, have a worldwide distribution. Ascaris infections induce strong Th2 responses in the host that appear to be central to the development of protective immunity. Th2 responses may be modulated actively through a complex host–parasite interaction that allows the parasite to survive but also limits severe Th2-mediated pathology in the host. The increased production of IL-10 by regulatory cell populations may have a key role in the modulation of the immune response during chronic ascariasis although most evidence in support is derived from experimental infections with A. suum and A. suum antigen extracts. Antigen fractions of A. suum have potent anti-inflammatory effects in experimental models of arthritis and asthma, but other antigen fractions are strong inducers of inflammation. The clinical effects of such immune modulation in humans is uncertain although there is some evidence that chronic infections may be associated with impaired immune responses to vaccines indicating potentially important effects on both mucosal and systemic immunity. Human ascariasis has been associated with an increased risk of asthma and other allergic reactions, observations that preclude the use of experimental infections for the treatment of inflammation in favor of the study of the anti-inflammatory properties of specific molecules derived from Ascaris.