Host Defenses to Protozoa

Robin Stephens, Jude E. Uzonna, Sara M. Dann

Research output: Chapter in Book/Report/Conference proceedingChapter


The innate and adaptive immune systems respond to the diverse protozoan pathogens with a wide array of weapons. Neutrophils, macrophages, and natural killer (NK) cells mediate the innate response against extracellular protozoan parasites. NK cell– and cytokine–activated macrophages are central to the killing of intracellular parasites. Dendritic cell (DC) responses play a central role in the induction of adaptive immunity by presenting antigens to T cells. For the intracellular pathogens (e.g., Plasmodium spp., Leishmania spp., Trypanosoma cruzi, Toxoplasma gondii), early production of interleukin-12 (IL-12) and interferon-γ (IFN-γ) drives the differentiation of CD4T cells to a protective T helper 1 (Th1) phenotype, amplifying innate cell parasite killing. CD8T cells can also play a critical role through cytokine production (e.g., Plasmodium spp., T. cruzi, T. gondii) or direct cytotoxic activity (e.g., Cryptosporidium). For the parasites that have an extracellular stage (e.g., Plasmodium spp., Trypanosoma spp., Giardia, and Trichomonas), specific antibodies from B cells also neutralize and opsonize, slowing parasite growth. Protozoan parasites utilize diverse mechanisms to evade the host immune response and establish chronic infection.

Original languageEnglish (US)
Title of host publicationClinical Immunology
Subtitle of host publicationPrinciples and Practice, Sixth Edition
Number of pages11
ISBN (Electronic)9780702081651
ISBN (Print)9780702081668
StatePublished - Jan 1 2022


  • Chagas disease
  • Cryptosporidium
  • Protozoa
  • Trichomonas vaginalis
  • amebiasis
  • giardiasis
  • host defense
  • leishmaniasis
  • malaria
  • toxoplasmosis

ASJC Scopus subject areas

  • General Medicine
  • General Immunology and Microbiology


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