PF4 and AIDS: While CXCL4 levels were higher among HIV− persons, this was also expected: we previously demonstrated among Multicenter AIDS Cohort participants that CXCL4 levels are lower among persons with failure to immune reconstitute on ART, [30] and in vitro data suggest that lower CXCL4 levels in HIV+ persons may be a marker of successful immune evasion by the virus [31].