Flow diagram of the model.

<p>Populations are represented by shapes: CD4+ T cells by pyramids, CD8+ T cells by inverted pyramids, macrophages by squares, MTB by a hexagon and HIV by a jagged circle. Interactions are represented by arrows: infection by a solid arrow, transition by a dashed arrow, release of pathogen by a broad speckled arrow, activation by a broad white arrow and elimination by an arrow with a cross. HIV infects CD4+ T cells and both resting and activated macrophages. HIV-infected T cells and MTB-infected macrophages first enter an eclipse stage and then a productive stage when they release pathogen before dying. In the model, HIV-infected macrophages do not pass through an eclipse stage because their life-span is relatively long. Some resting macrophages ingest MTB and become infected, whereas other resting macrophages become activated and are able to phagocytose and eliminate MTB. CD8+ T cells eliminate infected cells.