IFNG and infection: Further analysis of the clinical subgroups defined by clinical and immunological status showed that in contrast to the IFNγ responses used to define prior exposure, IL-2 responses were significantly elevated only in seropositive individuals (Group 3 and 5) regardless of symptoms during infection, while IL-1β release was elevated specifically in seropositive individuals who had convalesced from symptomatic infection (Group 5) (Figure 1B).