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KR Hartman, MK Mallet, J Nath and DG Wright
Department of Hematology, Walter Reed Army Institute of Research,
Washington, DC 20307-5100.
In an effort to characterize the cellular antigens recognized by anti-
neutrophil antibodies in autoimmune neutropenia, we studied sera, purified
immunoglobulin G (IgG) and isolated F(ab')2 from 70 neutropenic patients
suspected of this diagnosis. Anti-neutrophil antibodies were found in the
sera of 36 of these patients by either 125I-staph A binding or
immunofluorescence cytometric techniques that detected increased binding of
patients' IgG to normal neutrophils. Anti- neutrophil antibody positive
sera were then evaluated for specific binding to electrophoretically
separated neutrophil membrane-associated proteins by immunoblotting. A
43-Kd protein was consistently identified by eight anti-neutrophil antibody
positive sera. The specificity of binding to this protein was confirmed
with affinity purified IgG and F(ab')2 fragments prepared from these sera.
Sera from 20 healthy normal controls and from 22 non-neutropenic,
anti-neutrophil antibody negative rheumatoid arthritis patients failed to
bind this protein. Separate studies identified the 43-Kd protein as actin.
Purified Acanthamoeba actin comigrated with the protein and was
specifically bound by anti- neutrophil antibody positive IgG. Moreover, two
actin-specific monoclonal antibodies bound to the 43-Kd membrane-associated
protein in immunoblots. In addition, a rabbit anti-actin antiserum not only
bound to this same 43-Kd protein but also expressed anti-neutrophil
antibody activity against normal human neutrophils, as did purified human
anti- actin IgG prepared by affinity chromatography from the serum of one
of the index patients. These studies indicate that the anti-neutrophil
antibodies of certain patients with autoimmune neutropenia include
autoantibodies specific for actin. The molecules on the surface of
neutrophils, which have actin-like antigenic epitopes and are recognized by
these anti-actin antibodies, remain to be characterized.
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