Neonate alloimmune neutropenia (NAIN) is caused by the transplacental transfer of maternal alloantibodies directed against antigens on the infant’s neutrophils. To date, there are scant studies about its clinical characteristics and characterization of antineutrophil antibodies though some case reports are found. In this study we analyzed 11 cases with NAIN from January 2005 to December 2007. The diagnosis of NAIN was confirmed by the transient neutropenia less than 500/μl of absolute neutrophil count (ANC), the detection of maternal antineutrophil antibody, the incompatibility of neutrophil antigens between parents, and their mothers without autoimmune diseases. Antineutrophil antibodies were detected by granulocyte indirect immunofluorescence test using flow cytometry. To quantify the strength of the antibodies, the ratio of the mean fluorescence channel of each sample to that of control serum was expressed as relative fluorescence intensity according to the method reported previously (
Blood 99: 3468, 2002
). The median age at diagnosis in NAIN patients was 8 days after birth ranged from 0 to 30 days. The average of ANC at the presentation was 170/μl ranged from 0 to 500/μl. All antineutrophil antibodies detected in sera of both neonates and their mothers were against HNA-1 antigens. The alloantibody against HNA-1a was found in 2 cases, that against HNA-1b was in 6 cases, and that against FcγR IIIb was found in 3 cases. The fact that the frequencies of homozygote of HNA-1a and HNA-1b in Japanese population were approximately 50% and 12%, respectively may reflect the frequency of alloantibody specificity in NAIN. During the neutropenic period, 7 cases with NAIN showed mild to moderate infections associated with neutropenia, such as pyrexia and pyodermia. In contrast, 4 of 11 cases with NAIN did not have any infectious episodes in their clinical course. In all patients, the spontaneous recovery of neutropenia with the disappearance of alloantibody was observed within 6 months (median 85 days ranged from 3 weeks to 6 months). The duration until spontaneous resolution of neutropenia was dependent on the strength of alloantibody found in sera of the mothers and neonates. Two patients with significantly high strength of alloantibodies had the relatively long duration to restore the neutropenia(4 months and 6 months). In conclusion, the specificity of antineutrophil antibodies in patients with alloimmune neutropenia is dependent on the frequencies of neutrophil antigens in Japanese population. The quantification of alloantibodies in neonates and their mothers may be useful in considering the clinical course of neutropenia in neonates.
Disclosures: No relevant conflicts of interest to declare.
