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Control of immune complex and zymosan-mediated anaphylatoxin generation by proteins B and H of the alternative
The generation of histamine releasing activity (HRA) from human basophils in fresh serum by tetanus toxoid (Te)/anti-Te complexes or by zymosan can be modulated through introduction of incremental amounts of proteins B and H of the alternative complement pathway. Serum treated at 50 degrees in order to abolish alternative pathway-mediated haemolytic activity, lost 90% of its capacity to generate HRA upon addition of Te/aTe; such loss could be reversed through additions of purified B. Amounts of B sufficient to restore normal alternative pathway haemolytic activity also restored HRA induced by Te/aTe; as little as a 33% increase above the normal serum concentration of B increased the capacity to support Te/aTe induced HRA by a factor of 1.4. In contrast, additions of incremental doses of purified H to fresh serum reduced generation of HRA by both Te/aTe and zymosan. Total inhibition was achieved by increasing the serum H concentration by 12.5-30%; further increases of H up to 200% again permitted HRA generation induced by immune complexed aTe. H also inhibited Te/aTe induced HRA in a serum heated at 50 degrees but only 30% inhibition of HRA could be achieved over a range of H inputs up to 187% above normal serum concentration. Additions of H also inhibited HRA generation in fresh serum when induced with plain or C3b-coated zymosan (Z) particles. By increasing the serum concentration of H from 12.5 to 125%, dose-dependent inhibition of HRA generation was observed; the H input necessary to suppress 48% of HRA generation was ten times higher when HRA was generated by Z-C3b than by plain zymosan. Thus, the complement-dependent generation of HRA from fresh serum strongly depends on modest variations in the concentrations of the two regulatory proteins B and H of the alternative complement pathway, suggesting their direct effect on generation of anaphylatoxins C3a and C5a.
The generation of histamine releasing activity (HRA) from human basophils in fresh serum by tetanus toxoid (Te)/anti-Te complexes or by zymosan can be modulated through introduction of incremental amounts of proteins B and H of the alternative complement pathway. Serum treated at 50 degrees in order to abolish alternative pathway-mediated haemolytic activity, lost 90% of its capacity to generate HRA upon addition of Te/aTe; such loss could be reversed through additions of purified B. Amounts of B sufficient to restore normal alternative pathway haemolytic activity also restored HRA induced by Te/aTe; as little as a 33% increase above the normal serum concentration of B increased the capacity to support Te/aTe induced HRA by a factor of 1.4. In contrast, additions of incremental doses of purified H to fresh serum reduced generation of HRA by both Te/aTe and zymosan. Total inhibition was achieved by increasing the serum H concentration by 12.5-30%; further increases of H up to 200% again permitted HRA generation induced by immune complexed aTe. H also inhibited Te/aTe induced HRA in a serum heated at 50 degrees but only 30% inhibition of HRA could be achieved over a range of H inputs up to 187% above normal serum concentration. Additions of H also inhibited HRA generation in fresh serum when induced with plain or C3b-coated zymosan (Z) particles. By increasing the serum concentration of H from 12.5 to 125%, dose-dependent inhibition of HRA generation was observed; the H input necessary to suppress 48% of HRA generation was ten times higher when HRA was generated by Z-C3b than by plain zymosan. Thus, the complement-dependent generation of HRA from fresh serum strongly depends on modest variations in the concentrations of the two regulatory proteins B and H of the alternative complement pathway, suggesting their direct effect on generation of anaphylatoxins C3a and C5a.