Immune complex detection by immunofluorescence on polymorphonuclear leucocytes

Abstract

Polymorphonuclear leucocytes (PMN) from patients with systemic lupus erythematosus (SLE) were isolated from defibrinated and heparinized blood. In addition, PMN from a healthy donor were incubated with sera from SLE patients and with sera containing artificially prepared immune complexes of hepatitis B surface antigen (HBsAg) and human anti-HBsAg immunoglobulin (anti-HBs) with well defined variations of the antigen/antibody ratio. To one group of blood samples, 5 mM monoiodine acetic acid (MIAA) was added to block in vitro phagocytosis. The Pmn were examined for the presence of IgG, IgM, and HBsAg by the immunofluorescence technique. PMN from defibrinated blood of SLE patients showed in up to 80% immunoglobulin (Ig)-inclusions. However, addition of 5 mM MIAA reduced the number of Ig-containing PMN to at most 40%, which levels were equal to numbers found in specimens from heparinized blood. Addition of 5 mM MIAA to heparinized blood did not reduce the number of PMN with Ig inclusions. Normal donor PMN isolated from defibrinated, heparinized, and EDT blood showed equal amounts of Ig inclusions after incubation with SLE sera, but none when MIAA had been added. In PMN incubated with HBsAg-anti HBs immune complexes with an antigen antibody ratio between 5 and 0-2, both HBsAg and IgG could be detected. It is concluded that Ig inclusions in PMN from heparinized blood from SLE patients are due to in vivo phagocytosis, presumably of circulating immune complexes. In vitro phagocytosis of Ig from SLE sera by normal donor PMN also suggests the presence of immune complexes. Dependent on the antigen-antibody ratio, artificial HBsAg/anti-HBs immune complexes can be detected by in vitro phagocytosis by PM.