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Blood, Vol. 91 No. 1 (January 1), 1998:
pp. 181-186
By
From the Institute for Clinical Immunology and Transfusion Medicine,
Justus-Liebig University, Giessen, Germany; the Max von Pettenkofer
Institute, Ludwig-Maximilians University, Munich, Germany; and the
Department of Pediatric Hematology and Oncology, Hannover Medical
School, Hannover, Germany.
Primary autoimmune neutropenia (AIN) is caused by
granulocyte-specific autoantibodies and occurs predominantly in
infancy. Clinical presentation and diagnosis have not been well
established, resulting in burdening diagnostic investigations and
unnecessary treatment with granulocyte colony-stimulating factor
(G-CSF). In the present study, clinical, laboratory, and immunologic
data of 240 infants with primary AIN were evaluated. Suspected
association with parvovirus B19 infection was investigated using
serologic and DNA-based methods. Primary AIN was mainly diagnosed at
the age of 5 to 15 months but was observed as early as day 33 of life.
In 90% of the cases, AIN was associated with benign infections despite
severe neutropenia. Spontaneous remission, shown by 95% of the
patients, usually occurred within 7 to 24 months. Autoantibodies in the
patient's sera were not always present, and screening had to be
repeated several times until antibody detection succeeded. About 35%
of the autoantibodies showed preferential binding to granulocytes from
NA1 and NA2 homozygous donors. Bone marrow was typically normocellular
or hypercellular, with a variably diminished number of segmented
granulocytes. A significant association with parvovirus B19 infection
was not found. Symptomatic treatment with antibiotics was sufficient in
most patients. Eighty-nine percent of the patients received antibiotics
(cotrimoxazole) for prophylaxis of infections. For severe infections or
for surgical preparation, G-CSF, corticosteroids, and intravenous IgG
were administered, resulting in increased neutrophil counts in 100%,
75%, and 50% of the patients treated, respectively. In combination
with the detection of granulocyte-specific antibodies, the typical
clinical picture allowed diagnosis of AIN without burdening
investigations. Treatment with G-CSF was found to be a reliable
alternative to temporarily increase the neutrophil count.
AUTOIMMUNE neutropenia (AIN) is a
disorder caused by increased peripheral destruction of neutrophils as a
result of antibodies in the patient's blood that are directed against
their own neutrophils. It could not be convincingly shown until 1975
that neutropenia can be caused by granulocyte-specific
autoantibodies.1,2 Primary AIN, which is not associated
with other diseases such as systemic lupus erythematosus, is often
observed in infants.3,4 Although the etiology of the
disease is unknown, a recent report about a possible association of AIN
with Parvovirus B19 infection5 resulted in frequent testing
for this virus in patients with suspected AIN. Because of the
difficulties with the detection of granulocyte autoantibodies, many
questions concerning clinical course, diagnostic approach, immunology,
and therapy have remained open. In contrast to severe chronic
neutropenias (SCN) caused by disorders of myelopoiesis,6
AIN in infancy is less often considered in standard textbooks of
pediatric hematology. As a result, AIN is less known among physicians
and many cases are only diagnosed after expensive and burdening
investigations excluding other forms of neutropenia. This and the
availability of recombinant human granulocyte colony-stimulating factor
(G-CSF) for treatment of chronic neutropenia6 make an
accurate diagnosis of AIN necessary. Therefore, we evaluated the data
of 240 infants with primary AIN.
Patients and Sera
Detection of Granulocyte-Specific Autoantibodies
Location of Autoantigens For location of autoantigens, the recently described antigen-specific luminescence immunoassay monoclonal antibody-specific immobilization of granulocyte antigens (MAIGA) was used.8 Briefly, 1 × 106 neutrophils from one individual fixed with 1% paraformaldehyde were incubated (30 minutes at 37°C) with human serum and a monoclonal antibody (MoAb). In different reaction mixtures we used the MoAbs 3G8 (Immunotech, Hamburg, Germany) and Bw 209/2 (Behringwerke, Marburg, Germany), which are specific for the Fc
receptor IIIb, and the MoAbs 2E1, Bear 1, 7E4, and J3D3 (Immunotech),
which are specific for the Fc receptor II, the subunits of the
leukocyte adhesion molecule CD11b/CD18, and the C3b complement receptor
I. The cells were washed and solubilized by adding 100 µL of lysis
buffer (1% Triton-X 100, 5 mmol/L EDTA, 2 mmol/L phenylmethyl sulfonyl
fluoride, 0.5 µg/mL leupeptin, and 500,000 U/mL
aprotinin in 20 mmol/L Tris-buffered saline, pH 7.4) for 30 minutes at
room temperature. After sonication (2 minutes) and centrifugation at
15,000g for 30 minutes, the supernatant of each reaction
mixture was transferred to a separate tube coated with goat antimouse
antibodies. Unattached antibodies were removed by washing, and goat
antihuman IgG (heavy + light chain) antibodies conjugated
with peroxidase were added. After washing and subsequent addition of a
substrate containing luminol, hydrogen peroxide, and 4-iodophenol, the
emitted light (chemiluminescence) was measured over a period of 15
minutes in a luminometer (Lumat LB 9501; Berthold, Wildbad, Germany).
Serologic and Molecular Biologic Detection of Parvovirus B19 Testing for IgG and IgM antibodies to Parvovirus B19 by enzyme-linked immunosorbent assay (ELISA) and immunoblot and for Parvovirus B19 DNA by polymerase chain reaction (PCR) was performed as described previously.9,10
Clinical Presentation Patients. In 240 children tested, positive antineutrophil antibodies could be detected. Female to male distribution was 54%:46%. All patients were white and less than 3 years of age. Diagnostic testing of these children with positive antibody results did not show any other conditions than neutropenia (primary AIN). Five patients appeared to have AIN, but granulocyte antibodies could not be detected even though they were tested three times. After the granulocyte count began to increase, no further testing was performed. Although the clinical picture did not differ from the other 240 patients, as a result of the failure to detect antibody, these patients were not included in the study. It appears likely that they had AIN, but, at the time of diagnosis, spontaneous remission of neutropenia had already begun. At that time granulocyte autoantibodies are no longer detectable in the patient's blood.
Laboratory Findings
Blood count.
At the time of diagnosis, the neutrophil counts in the peripheral blood
were distributed as follows: 70% had greater than 500 cells/µL, 23%
had between 500 and 1,000 cells/µL, and 7% had between 1,000 and
1,500 cells/µL. Neutrophil counts varied significantly between 0 and
1,500/µL during the neutropenic phase in 30 patients who were tested
repeatedly during the neutropenic period. Monocyte counts of more than
1,000 cells/µL were found in 28% of all patients. Eosinophilia was
only observed in 1 case.
Bone marrow findings.
Bone marrow findings are summarized in Table
2. Ninety-seven percent of the patients
showed normal or increased cellularity with or without a reduced number
of metamyelocytes, bands, and mature neutrophils. Although in some
cases a maturation arrest seemed to occur, in all cases maturation
reached at least the myelocyte/metamyelocyte stage. Phagocytosis of
granulocytes by bone marrow macrophages was observed in 5 cases,
indicating that removal of sensitized granulocytes already occurs in
the bone marrow.
Immunohematologic findings.
Granulocyte-specific antibodies were detected in 74% of the cases in
the first investigation. In 26%, repeated antibody testing with
additional blood samples from the same patient up to three times at
intervals of 2 to 4 weeks was necessary for detection of antibodies.
The GIFT was more sensitive in detection of granulocyte autoantibodies
than the GAT (Table 3). Cytotoxic or
noncytotoxic HLA antibodies were detectable in none of the sera.
Ninety-seven percent of the sera contained granulocyte autoantibodies
of the IgG type, and 15% of the sera contained granulocyte
autoantibodies of the IgM type. In 30 of 60 sera tested,
granulocyte autoantibodies activated complement and 15 reacted
positively in the granulocyte cytotoxicity test.
Parvovirus B19 diagnostics.
A total of 110 patients were tested for Parvovirus B19 infection.
Thirty-six patients showed threshold values in ELISA (IgG and IgM; n =
9), in immunoblot (n = 12), and/or by virus-specific PCR (n =
28). Serum samples from 24 of the 36 patients were retested for
Parvovirus B19 antibodies after spontaneous remission of neutropenia
and all were found to be negative.
Treatment and Prognosis
In this study we present 240 children with primary AIN. The
differential diagnoses of AIN of infancy are alloimmune neonatal
neutropenia, cyclic neutropenia, and SCN. Alloimmune neonatal
neutropenia, which can last up to 6 months, could be excluded by the
detection of granulocyte alloantibodies in the maternal
serum.7 Cyclic neutropenia is typically characterized by
neutropenic periods of 3 to 6 days occurring approximately every 21
days. In AIN, neutrophil counts can also vary considerably from day to
day. Based on inadequate serial data, a number of cases reported as
cyclic neutropenia were probably AIN.11 In contrast to AIN,
SCN is characterized by severe infections already in the first month of
life, no spontaneous remission of neutropenia, and a maturation arrest
of myelopoiesis at the promyelocyte stage. The promyelocytes are
frequently morphologically atypical with vacuolization and atypical
nuclei, but findings are variable.6 Overall, the number and
severity of bacterial infections is much lower in AIN than in SCN.
However, severe infections can occur in AIN patients and the
antibody-mediated destruction of segmented neutrophils and band forms
can mimic maturation arrest in the myelocyte/metamyelocyte stage. In
addition, 3% of all AIN patients present a hypocellular marrow that is
probably caused by antibodies binding not only to mature neutrophils
but also to primitive hematopoietic cells.12 Therefore,
differential diagnosis of SCN and AIN often depends on the detection of
granulocyte-specific antibodies in the patient's sera. Testing the
sera of 10 patients with SCN, we found no evidence of granulocyte
antibodies. AIN is far more frequent than SCN, with
1:100,00013 versus 1:1,000,000,6 and very
probably the incidence of AIN is much higher. Therefore, it is
justified to postpone bone marrow examination until antibody screening
shows a negative result. In case of a positive result, there is usually
no need for bone marrow aspiration or biopsy.
Submitted March 19, 1997;
accepted August 22, 1997.
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