Granuloma formation

• M. tuberculosis has been phagocytosed but not killed by the macrophage

• T_H1 cell interacts with MHC class II and secretes IFNγ to increase effectiveness of macrophage digestion

• when European Christian missionaries went to the pacific islands, they took with them tuberculosis and leprosy. unfortunately for the pacific islanders, the ability to counter infections is dictated not only by recognizing pathogens antigenically but also by having sufficiently-amplified lysosomal activity

• Asians, Pacific Islanders, and American Indians in the tropics were often infected with parasites, which caused a selection bias for T_H2

• they were then exposed to diseases brought in by people who were T_H1-dominant, including viruses such as smallpox and bacteria such as Yersinia pestis

• this may have been one of the reasons why the Hawaiians had so much trouble with leprosy

• Micrograph of a granuloma

  • caseating granuloma —the inside of the granuloma is necrotic

  • this should make you think of tuberculosis. that’s because the purpose of creating a granuloma is to create an ischemic environment with the ultimate purpose of killing M. tuberculosis, an obligate aerobe

  • but there may be many live M. tuberculosis organisms in the non-necrotic areas

  • to keep the Mycobacteria bottled up, T-cell stimulation is required to keep the macrophages alive and healthy

• our immune system does not kill all organisms. sometimes it just captures the organism and holds it down

  • Herpes simplex lives in single peripheral nerves

  • Herpes zoster lives in nerve roots; therefore, it affects a whole dermatome

  • Epstein-Barr virus lives in your body but is constantly suppressed

Category: Pathology Notes