Correlation of disease activity and Clq-binding immune complexes with the neutrophil inclusions which form in the presence of SLE sera

Abstract

Intracytoplasmic inclusions containing immunoglobulin (Ig) and complement (C3) are found in normal neutrophils (PMN) after incubation with sera from patients with SLE. These inclusions are believed to be immune complexes removed by phagocytosis from the SLE patients' sera in vitro. Similar inclusions were also noted in the circulating PMN from some patients with SLE. In the present study we have examined the relationship between the presence of intracytoplasmic inclusions and various clinical and laboratory features of SLE. Blood from forty-five patients with SLE was drawn and separated at 37°C. Fresh heparinized blood was also obtained from normal volunteers and allowed to stand for 90 min at 37°C. The buffy coat cells from both normal and SLE groups were removed, centrifuged, washed and examined (direct method) or incubated in the SLE sera for 90 min at 37°C (indirect method). Slides of washed cells were prepared in the cytocentrifuge, stained with fluorescein-conjugated goat anti-human IgG, IgM, IgA and C3 and examined under ultra-violet light.

By the direct method, 24% of patients had small intracytoplasmic inclusions in their neutrophils when stained for IgG suggesting that immune complexes were phagocytosed in vivo. None of twenty-one normal controls had similar inclusions. By the indirect method, 62% of SLE patients were positive for IgG, 15% for IgM, 8% for IgA and 31% for C3. None of the twelve normal controls were positive.

By the indirect method, PMN inclusions containing both IgG and IgM correlated with clinical activity (P<0·001), depressed serum complement (CH50, P=0·026; and C3, P<0·051), cryoglobulinaemia (P=0·014), anti-nDNA antibodies (P<0·001) and Clq-binding immune complexes (P=0·008). A suggestive correlation with granulocytopenia was also observed. The presence of inclusions containing IgG alone did not correlate with any of these parameters. C3 and IgM appeared to be mutually exclusive, i.e. neither was present simultaneously. These findings suggest (1) that normal PMN on exposure to SLE sera develop intracytoplasmic inclusions by phagocytosis of immune complexes, (2) the presence of such complexes correlates with a number of parameters of disease activity, particularly when IgG and IgM are both present and (3) such complexes may be phagocytosed in vivo as suggested by the presence of inclusions in vivo and contribute to a number of granulocyte disturbances seen in patients with SLE. These abnormalities in granulocyte function may be important, predisposing factors for infection in patients with active SLE.