Macrophages infected with Mycobacterium tuberculosis (green) which have been stained for inducible nitric oxide synthase (iNOS) shown in red, an enzyme that catalyzes the production of nitric oxide from L-arginine to restrict bacterial growth. The nucleus of the infected cells is shown in blue. Credit: Miljan Stupar

Intestinal inflammation with epithelial cells (green) exhibiting cell death (marked by cleaved caspase 3 in red). Credit: Dr. G. Sonnenberg.

Innate lymphocytes (red and green) interacting with microbiota-specific regulatory T cells (blue, green and cyan) in lymphoid tissues. Credit: Dr. G. Sonnenberg.

Mycobacterium smegmatis elongates predominantly from one of the two cells poles. Credit: of Drs. H. Botella and S. Ehrt.