A systematic study of neutrophil degranulation and respiratory burst in vitro by defined immune complexes

Defined immune complexes (IC) were used to compare the effect of antibodies of different classes and subclasses on neutrophil respiratory burst and degranulation. IC were made from 5-iodo-4-hydroxy-3-nitrophenacetyl (NIP) conjugated to bovine serum albumin (BSA) and chimaeric mouse-human anti-NIP monoclonal antibodies including IgA2, IgE and all four IgG subclasses. The activation of neutrophils by IC depended on antibody class and subclass, on antigen epitope density, on antigen: antibody ratio and on the medium used. The ability to generate the respiratory burst showed a different pattern to the ability to give rise to degranulation. Compared with other IC, IgA2 IC provided the strongest stimulus for neutrophil activation. IgG1 IC, IgG2 IC and IgG4 IC activated neutrophils moderately or weakly IgG3 IC were unable to stimulate the respiratory burst, but could cause strong degranulation. IgE IC could hardly cause any neutrophil response. Neutrophil degranulation in response to IgG3 IC in serum-free medium or heat-inactivated serum was fast, and it quickly reached maximum. Degranulation caused by IgA IC was relatively slow, but gradually increased during incubation. The activity of IgG1 IC, IgG2 IC and IgG4 IC generated a respiratory burst increased with antibody excess and decreased with antigen excess. The activity of IgA2 IC, however, was not affected by change of antigen and antibody ratio. A specific role of serum, possibly due to complement, was found in enhancing degranulation, both temporally and quantitatively, by IgA2 IC.