Suppression of mitogen-induced lymphocyte transformation by plasma from patients with hepatosplenic Schistosomiasis mansoni: role of immune complexes

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Abstract
Plasma from chronic or advanced hepatosplenic schistosomiasis (mansoni) patients (PCS) suppressed mitogen-induced responses of normal human peripheral blood mononuclear cells. 1 × 105 Ficoll-Hypaque isolated lymphocytes were cultured in 100 μ1 RPMI 1640 media with 100 μ1 plasma preparation and stimulated with phytohemagglutinin P (PHA), concanavalin A (Con A), pokeweed mitogen (PWM) and Staphylococcus aureus phage lysate (SPL). Compared to normal human plasma, dose-response experiments with 10–50% PCS uniformly inhibited the 72-h PHA, Con A and PWM responses with maximal suppression at 50% plasma concentration. At this concentration, the range of suppression was 42–60%. The inhibitory activity was unaffected by 56°C, 30 min pretreatment of PCS. However, pre-culture of cells with PHA for 24 h prior to addition of 50% PCS abrogated the suppressor activity. Furthermore, 6-day cultures with PWM and SPL were not suppressed by 50% PCS. Plasma suppressor activity was nearly eliminated by pre-treatment of PCS with 4% (w/v) polyethylene glycol (PEG) in all cases. In the putative immune complexes in the PEG precipitates, C1q, C3, C4, IgG, IgM and IgA were identified in nearly all PCS samples. Schistosomal antigen was found in only two of 23 PCS samples tested and significant anti-schistosomal IgG antibodies were found in all PEG precipitates. The data suggest immune complexes (non-specific and specific) act to suppress 72-h mitogenic responses.