Neisseria meningitidis inside neutrophils, revealing properdin deficiency

A 20-month-old baby boy was referred to the pediatric emergency unit for hypotonia, fever and necrotic purpura. A suspected septic shock, complicated by disseminated intravascular coagulation, led to transfer to intensive care. Complete blood count disclosed leucopenia (2.58 × 109/L) with neutropenia (0.28 × 109/L) subnormal lymphocytes (2.13 × 109/L) and 3% metamyelocytes. Attentive examination at ×50 magnification detected bacteria in neutrophils (Figure 1). Oriented by the neurological signs and purpura, these pathogens were identified as Neisseria meningitidis by Multiplex Polymerase Chain Reaction on a serum sample and characterized as a W135 serotype. Unfortunately, the infectious situation could not be controlled, and the child died 48 h after admission. Even though opsonization was obviously efficient, as witnessed by the presence of phagocytosed bacilli, complement explorations were carried out and revealed an impairment of the alternative pathway (AP50 <10%, properdin antigen 2 mg/L). A variant (mutation) of the properdin gene was found on exon 3 p.CysTyr (c.95G > A). It was also found, heterozygous, in the mother who has a normal level of properdin. Properdin deficiency, a rare X-linked disorder associated with increased susceptibility to Neisseria spp., does not impair phagocytosis (as shown here) but leads to inefficient bacteria-killing likely related to its absence in neutrophil granules (Wirthmueller et al., 1997Wirthmueller U. Dewald B. Thelen M. et al.Properdin, a positive regulator of complement activation, is released from secondary granules of stimulated peripheral blood neutrophils.J Immunol. 1997; 158: 4444-4451Crossref PubMed Google Scholar). There was no specific funding for this work.