Ultrastructural and biochemical observations on antineutrophil antibody- and complement-induced immuno-injury to equine neutrophils.

ABSTRACT

Antibody-induced damage to neutrophils was studied to elucidate processes associated with destruction of neutrophils in immune-mediated neutropenias. Cytomorphological changes and release of certain cellular constituents were determined for neutrophils treated with an antineutrophil serum in the presence or absence of rabbit complement. Neutrophils exposed to the antineutrophil serum alone showed endocytotic vacuoles and degranulation. In contrast, neutrophils exposed to the antineutrophil serum and complement showed marked morphologic changes. The plasma membrane developed numerous vesicles, villous processes and minute areas of bilayer discontinuity. Highly damaged cells exhibited cellular and nuclear swellings, disruption of cytoplasmic integrity and disordered distribution of lysosomal granules. Cytoplasmic constituents (K+ and lactate dehydrogenase) were released extracellularly from neutrophils exposed to the antineutrophil serum with or without complement. Cytological changes induced by the antineutrophil serum and complement were analogous to those reported for leucocytes exposed to the activated complement components C5b-9 (the membrane attack complex) and bacterial toxins. It was concluded that the cytological abnormalities observed were most probably associated with immune-mediated damage to the cell membrane, leading to leakage of cytoplasmic constituents like K+, colloidal osmotic swelling, and disruption of the cytoskeletal system.