Leprosy is caused by infection with Mycobacterium Leprae. In one form of the dis

Question

Leprosy is caused by infection with Mycobacterium Leprae. In one form of the disease, tuberculoid leprosy, few live bacteria are found and although the skin and peripheral nerves are damaged by inflammatory responses, the disease progresses slowly and the patient survives. In the other form, lepromatous leprosy, copious antibodies are produced but gross tissue destruction occurs and the disease is eventually fatal. Which form of CD4 cell response (Th1 or Th2) do you think is induced in each form of the disease and how does it contribute to the outcome?

Explanation / Answer

Answer:

1. Tuberculoid leprosy: strong Th1 response

Infection with Mycobacterium leprae can produce paucibacillary disease, characterized by well-formed granulomas and a Th1 T-cell response.

The result is:

i. Low number of bacilli (due to Th1 response)

ii. Fewer lesions: macular, nerve enlargement, paresthesia

iii. Damage from immune response (granuloma formation, nerve enlargement, damage: loss of sensation)

2. Lepromatous leprosy: strong Th2 response & reciprocal inhibiton of Th1

It results from the failure of Th1 cell activation which is necessary to eradicate the mycobacteria (Th1 response is required to activate macrophages that engulf and contain the disease). In lepromatous leprosy, Th2 response is turned on, and because of reciprocal inhibition (IL-4; IL-10), the cell-mediated response (Th1) is depressed.

The result is:

i. Numerous lesions: nodular, leonine facies, loss of eyebrows, destruction of nasal septum, paresthesias

ii. Damage from large number of bacili (nerve damage from overgrowth, loss of sensation)

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