FIGURE 1.

Biological characteristics of macrophage reservoirs. (A) Unpolarized macrophages are stimulated by the local cytokine milieu in different tissue compartments, which causes different macrophage polarization states. Macrophage polarization is a spectrum and reversible. Two extremes are the M1, classically activated or pro-inflammatory, macrophage and the M2, alternatively activated or anti-inflammatory, macrophage, who play different roles within the body. Upon HIV-1 infection, polarization states affect susceptibility of macrophages as well as inhibit viral replication at different points in the HIV-1 replication cycle. (B) Tissue resident macrophages are sustained by self-renewal, and in some tissue, infiltrating macrophages will replenish tissue resident macrophage populations. Both monocyte derived macrophages and tissue resident macrophages are susceptible to HIV-1 infection and can sustain long-term infection with tissue resident macrophages maintaining viral infection for years to decades. (C) Virus containing compartments (VCCs) are formed from the introduction of gag synthesis in the cytosol, promoting the formation of compartments. Viral particles assemble then bud into these VCCs, accumulating over time. Upon cell necrosis or stimulation from the microenvironment, VCCs may release their viral particles.