A Fully Differentiated Macrophage Infection Model of Monocyte-Derived Cells with Mycobacterium tuberculosis

Obtain a culture of fully differentiated macrophages in a multi-well plate. These macrophages have surface markers, such as toll-like receptors or TLR-2 — a pattern recognition receptor that identifies various microbial components.

Add an appropriate amount of fluorescently labeled Mycobacterium tuberculosis or Mtb cell suspension into each well and incubate.

TLR-2 recognizes lipoarabinomannan, or LAM, a complex glycolipid component of the Mtb cell wall, initiating phagocytosis. The macrophage internalizes Mtb, sequestering the bacterium within a phagosome — a membrane-bound compartment.

The phagosome matures, by fusing with lysosomes, forming a phagolysosome — an acidic and enzymatic-rich compartment.

Within the phagolysosome, the Mtb inhibits the vacuolar-type proton pump responsible for generating an acidic pH. Consequently, the pH within the phagolysosome becomes near-neutral, deactivating enzymes that degrade engulfed pathogens.

The interaction between LAM and TLR2, also affects host cell signaling pathways, leading to the modulation of surface markers involved in antigen presentation.

The inactivation of phagolysosome and inhibition of host immune response enable Mtb to persist and replicate within the macrophage.