BENGALURU: Researchers at the Indian Institute of Science (IISc) have designed a novel 3D hydrogel culture system that mimics the mammalian lung environment, which can track and study how tuberculosis bacteria infect lung cells and test the efficacy of therapeutics used to treat TB.
Scientists opined that the current culture models used to study TB infection have several limitations.
They are typically culture plates that are monolayered and do not accurately mimic the 3D microenvironment inside the lungs. The microenvironment experienced by the cells in such 2D culture is vastly different from the actual extracellular matrix (ECM) surrounding lung tissue.
“In a tissue culture plate, there are no ECM molecules, and even if a very thin layer of ECM is coated on these plates, the lung cells ‘see’ the ECM on one side at best,” said Vishal Gupta, PhD student at the Department of Bioengineering (BE) and first author.
The team has now designed a 3D hydrogel culture made of collagen, a key molecule present in the ECM of lung cells. Collagen is soluble in water at a slightly acidic pH. As the pH is increased, the collagen forms fibrils which cross-link to form a gel-like 3D structure.
At the time of gelling, the researchers added human macrophages – immune cells involved in fighting infection – along with TB. This entrapped both the macrophages and the bacteria in the collagen and allowed the researchers to track how the bacteria were infected.
The team tracked how the infection progressed over 2-3 weeks. The cells stayed viable for three weeks in the hydrogel – current cultures are only able to sustain them for 4-7 days.
The team also tested the effect of pyrazinamide – one of the four most common drugs given to TB patients. They found that even a small amount (10 µg/ml) of the drug was quite effective in clearing out infection in the hydrogel culture.
Previously, scientists have had to use large doses of the drug – much higher compared to concentrations achieved in patients – to show that it is effective in tissue culture.
“Nobody has shown that this drug works in clinically relevant doses in any culture systems. Our setup reinforces the fact that the 3D hydrogel mimics the infection better,” explained Rachit Agarwal, Associate Professor at BE.
Researchers plan to mimic clusters of infected white blood cells to understand why some people have latent TB, while others show aggressive symptoms.