Well I think the cause in TB is that areas infected by bacteria are surrounded by lymphocytes. They tend to clump around the area which forms a granuloma.

Yeah that’s right. Don’t know about sarcoidosis but I had an exam last week on TB so here is my summary of what causes it.

The Mycobacterium tuberculosis rods are engulfed by alveolar macrophages. This kills about 90% of the rods but the remaining 10% evade the host cell’s microbicidal killing. They can do this by preventing oxidative burst, inhibit phagosome lysosome fusion, resist degradation by lysosomal enzymes by releasing lipoarabinomannan, or rods may escape from the phagosome into the cytoplasm, etc.
Rods which are not destroyed multiply intracellularly and are released on macrophage death (forming the Ghon focus). They are then engulfed by unactivated macrophages. The phagocytic vacuole in unactivated macrophages provides an ideal environment for rods to multiply logarithmically. These macrophages are then activated and they aggregate to form the granuloma. A compact palisade, of many cells thick of macrophages around the focus of infection. They may then fuse to form giant multinucleate cells. The palisade consumes all the oxygen but the centre is starved of it and leads to necrosis; caseation occurs.

Hope that helps. Maybe a bit too much info but I think thats better than not enough! 😉