FIG. 3.

Low levels of anti-streptococcal superantigen neutralizing antibodies in patients with severe and nonsevere invasive group A streptococcal infections. Neutralizing antibodies against the mixture of superantigens produced by the M1T1 isolates in plasma specimens of patients infected with indistinguishable M1T1 strains were evaluated. PBMC (10⁶ cells/ml) from a healthy donor were stimulated either with phytohemagglutinin (1 μg/ml) or with the partially purified culture supernatant from M1T1 isolates (diluted 1:100 in RPMI) in the presence of 5% FBS or 4% FBS plus 1% plasma. (A) Neutralizing activity in plasma specimens from healthy individuals (n = 20) of different ages. (B) Neutralizing activity in plasma specimens from patients with severe (n = 21) and nonsevere (n = 12) infections and healthy controls (n = 20) against pure superantigens rSpeA and SpeB. Proliferation was assessed after 3 days of culture, and the mean counts per minute ([³H]thymidine uptake) ± SEM for triplicate cultures was calculated. Neutralizing activity is expressed as percent inhibition of mitogenic activity. (C) Results for patients with severe (n = 21) and nonsevere (n = 12) invasive disease or for age-matched healthy individuals who reside in the same area. Each patient plasma was tested for neutralizing activity against the isolate from that patient, or, in the case of the age-matched healthy individuals, supernatants from six representative isolates (three from severe cases and three from nonsevere cases) were used for stimulation. Proliferation was assessed after 3 days of culture, and the mean counts per minute ([³H]thymidine uptake) ± SEM for triplicate cultures was calculated. Neutralizing activity is expressed as percent inhibition of mitogenic activity.