Immune reconstitution, or the reversal of HIV-related immune system decline, is one of the primary goals of highly active antiretroviral therapy (HAART). Reconstitution involves an increase in functional CD4 cells to guide the immune response against pathogens such as HIV, resulting in the suppression of viral load and other beneficial outcomes. However, immune reconstitution may trigger an inflammatory reaction in some people soon after they begin anti-HIV therapy and show signs of immunological improvement. Known as immune reconstitution syndrome (IRS) or immune reconstitution inflammatory syndrome (IRIS), this set of symptoms often resembles an AIDS-defining illness or other condition seen in people with HIV. While in most cases the symptoms of IRIS resolve after a few weeks, the syndrome may be severe or mistaken for true disease progression, and should be properly diagnosed and treated.