Autoimmune Neutropenia of Infancy Is Almost Exclusively Caused By IgG Antibodies

Background The relevance of IgM antibodies in autoimmune mediated hemocytopenias remains a matter of debate. For autoimmune neutropenia, conflicting results were published. This study was performed as part of the Giessen Neutropenia Registry, which prospectively included children with suspected autoimmune neutropenia. Methods Children with suspected autoimmune neutropenia were prospectively enrolled and data central to their suspected diagnosis were collected over 3 years. Sera were tested for the presence of autoantibodies against neutrophils by granulocyte immunofluorescence test (GIFT) and granulocyte agglutination test (GAT). The presence of IgG and IgM antibodies was assessed in a subgroup of patients with positive initial GIFT in whom spontaneous remission of their neutropenia was documented. Results A total of 406 children were included in the study. A remission was reported for 114 patients during the study period. Of those, 96 children (84%) had an initial positive GIFT. Their median age at diagnosis was 11 months (7-17.5), and their mean neutrophil count was 293 (±267)/µL, ranging from 0 to 975. In total 75/96 (78%) of children had at least one documented infection at diagnosis. In 29/96 (30%), a bone marrow aspirate was available. At the documented time point of remission, children were 27 months (18-41) old. In the initial sample send for diagnosis, IgG antibodies against neutrophils were detected in 94/96 children (98%), and IgM antibodies were detected in 2/96 (2%). We did not observe children with autoantibodies of both Ig classes. Conclusion To our knowledge, this is the first study to demonstrate the contribution of IgG or IgM antibodies in a well-defined clinical cohort with a typical course including, spontaneous disease remission. IgG antibodies were present in 98%. Only very rarely, IgM antibodies can be detected. We conclude that in general, screening for IgG autoantibodies is appropriate as a first diagnostic step. In cases with strong clinical suspicion but negative GIFT with anti-IgG, anti-IgM testing may be considered.