As HIV patients take their HAART for the first time, they get a rebound in their CD4 counts and can become symptomatic for a variety of infections that were there, but asymptomatic due to the lack an inflammatory response.
Non HIV patients who can get IRIS: recovering neutropenics with hepatosplenic candida (PubMed) and aspergillus and post partum (PubMed). In neutropenics with aspergillus, IRIS is a good prognostic sign.
As part of IRIS, HIV patient can get a CD8 encephalitis (PubMed) that is treated with steroids.
Per the infecting organism.