FIG. 3.

SAg-neutralizing capacities of selected SAB sera from IDUs (A) and nonaddicts (B). The neutralizing capacities of SAB sera (acute phase and convalescent phase) against (i) the supernatant from the infecting strain and (ii) representative recombinant SAgs were determined. Therefore, S. aureus culture supernatants or recombinant SAgs were incubated with serial dilutions of SAB sera. After 20 min, 10⁵ PBMCs were added and T cell proliferation was measured after 72 h by [³H]thymidine incorporation. The graph depicts the SAg-induced proliferation in the presence of serum, expressed as percentages of the control without human serum. In contrast to nonaddicts, most IDUs had neutralizing antibodies already at the acute phase of SAB and antibody titers increased more frequently. In general, neutralizing antibodies against egc SAgs were absent and were not induced. Representative data sets are depicted (IDUs, 7/25; nonaddicts, 6/37).