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Here is the original slide:

I am thinking about the "cord factor" sentence in a more general case.

Assume you inhibit Leucocytes migration. How does this lead to accumulation of macrophages in the site of infection?

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Can you edit your question to be more specific, and not use "Leu" as an abbreviation ? (Leu has other meanings). Leukocytes come in many types - lymphocytes, macrophages and neutrophils, for example. The effects of inhibiting their migration may vary. What specifically do you want to know? I'm not sure if your example with Cord Factor is a suitable basis for your question...According to this cord factor is generally pro-inflammatory and acts by preventing fusion between vesicles that may contain M.tuberculosis and lysosomes. –  PlaysDice Mar 29 at 16:38
    
Can you provide a link to the original document that includes your sentence ? That might help us. –  PlaysDice Mar 30 at 12:31
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I edited your question both to add your image of the slide and to remove your "quote", which was not at all what the slide said. Also, it should be clarified here that cord factor comes from M. tuberculosis. –  MattDMo Mar 30 at 18:45
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The only reference I can find re cord factor inhibiting leukocyte migration is this one . It cites reference 33 as a basis for that statement and I don't see any such finding there. Skimming the abstracts of references 32 and 34 also don't seem to suggest such a finding, either. So I think the premise of the question may be in error. If you can find a reference for such activity, then I think we can look at any such specific activity. Basically, I think that part of the slide is wrong. –  PlaysDice Mar 30 at 21:29

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The mechanism is likely very straightforward. Activated macrophages already in the area are releasing pro-inflammatory cytokines like TNFα, IL-1β, IL-6, IL-12, MIP-2, etc. These are not only important for granuloma formation, but they also recruit other immune cells to the area. However, since cord factor has this anti-migratory effect, once the cells get there they can't leave. This is important because activated macrophages are key antigen-presenting cells (once they kill and break down the antigen, in this case Mycobacteria), and they need to move to the spleen to assist in the upregulation of the adaptive immune response. By preventing this, mycobacteria can evade part of the immune system - part of the reason why TB is so hard to clear once acquired.

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