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Discussion Starter #1
a 34 year old female immigrant from eastern Europe presents to the outpatient clinic with chronic cough. She has lost 5 Kilograms in the past three months. She also complains of occasional mild hemoptysis. An intradermal injection is done, and after 2 days the site of injection becomes indurated and erythematous. Which of the following is directly responsible for this observation:

a- alpha interferone
b- absence of MHC I on the surface of affected cells
c- CD 8 cells
d- IL-12
e- IL-4
f- invasion by bacteria
g- invasion by fungus
 

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a 34 year old female immigrant from eastern Europe presents to the outpatient clinic with chronic cough. She has lost 5 Kilograms in the past three months. She also complains of occasional mild hemoptysis. An intradermal injection is done, and after 2 days the site of injection becomes indurated and erythematous. Which of the following is directly responsible for this observation:

a- alpha interferone
b- absence of MHC I on the surface of affected cells
c- CD 8 cells
d- IL-12
e- IL-4
f- invasion by bacteria
g- invasion by fungus
It is type IV mediated hypersensitivity, therefore, a antibody independent response will be present.
not sure but could be CD8 cells, (c). ???
 

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TB Mantoux test

The patient has TB, the skin test described was Mantoux test (PPD). Therefore it is Type IV hypersensitivity, CD 8 is the correct answer.
 

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Discussion Starter #5
The first step in the specific response to an antigen is its engulfment by Antigen Presenting Cells (APC) that present the antigen to CD4 cell types. The next step is pivotal and determines the fate of the immunological response.

-If Th1 cells are activated by IL-12 the response will be mainly cellular (cell mediated immunity). Th1 cells produces IL-2 activating more CD4 cells, and IFN gamma which activates macrophages. Macrophages release TNF and IL-1 activating more CD4 cells which secrete more IFN gamma. The latter converts macrophages into epithelioid cells and langhans giant cells, resulting in the formation of a granuloma, and type 4 hypersensitivity.

-On the other hand if Th2 cells are activated instead by IL-4, the response will be humoral and allergic. Because these cells produce IL-4 and IL-5 which mediates class switching in B-cells resulting in secretion of IgE (and IgA), and recruitment of eosinophils (IL-5 action). This is the pathophysiological mechanism of allergic diseases including asthma.

In the question the presentation is suspecious of TB, the injection as been said is PPD which stands for Purified Protein Derivetive (of M. tuberculosis) not the complete organism. The reaction seen is a type 4 hepersensitivity response to PPD.

a- gamma interferone not alpha interferone is responsible for mediating type 4 hypersensitivity. Patients with decreased IL-12 receptor are susceptible to TB and are treated with IFN gamma which is the ultimate result of IL-12 activating Th1 cells. Alpha and beta IFN work by decreasing viral protein synthesis.
b- Absence of MHC I on cells activates NKCs, and its presence inhibits NKCs, this does not have a major role in type 4 hypersensitivity.
c- Unlike one might expect from their name Cytotoxic T cells are not the major responsible for type 4 cell mediated hypersensitivity, it is the interaction between macrophages and CD4 Th1 cells that contribute to the greatest extent to the formation of granuloma.
d- IL-12 is the correct answer.
e- IL-4 would result in humoral mediated immunity through activation of Th2 cells and class switching of B-cells.
f- The injected material is not the live M.TB bacteria, it is a Purified Protein Derivative from it.
g- The presentation is more suspecious of TB, even if it was the fungus or the live bacteria that is injected, it is the Th1 immunological response that mediates the response to it, not the direct invasion of the organism

The high yield information is in bold.
 
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