This study consists of 3 groups and 8 [AS PER AMENDMENT 4/17/01: 6] subgroups. Clinical microbiological data are collected and samples are obtained for immunologic assays (pathogen-specific and general) in all groups at entry (time of OI presentation for Group 1 patients) and at 12 weeks (except Group 3b). Group 1b patients also are evaluated at 24 weeks [AS PER AMENDMENT 4/17/01: The following text has been deleted: and at the time of diagnosis of immune-recovery vitreitis, if it should develop]. [AS PER AMENDMENT 4/17/01: Once patients in Groups 1, 2, and 3a have completed the Week 12 evaluations, they will be off-study.] Blood samples, 1 to 7 days apart, for peripheral blood mononuclear cells (PBMCs), LPA, and inducible cytokine expression of interferon gamma, interleukin-2, interleukin-4, and interleukin-10 are obtained.