Chance Detection of CD16 Deficiency on Polymorphonuclear Neutrophils in Iron Deficiency Anemia.

Introduction CD16 (FcgRIII) is a low affinity receptor for immunoglobulin G(IgG)constitutively expressed on polymorphonuclear neutrophils, monocytes and NK-cells with various effector functions including phagocytosis of opsonized particles or of immune complexes and in antibody-dependent cellular cytotoxicity (ADCC). Congenital defect of neutrophil CD16 expression has been reported with variable phenotypic associations such as anaemia, neutropenia, autoimmune thyroiditis, recurrent infections, acute myeloid leukaemia, systemic lupus erythematosis and in mothers whose newborns have developed transient neonatal alloimmune neutropenia.

CD 16 deficiency on neutrophils -A 46 year old lady presented with extreme tiredness with her full blood count showing Hb 7.6 g/L MCV 76.0 fl MCH 23.8 pg WBC 5.9 X 10^9/L Neutrophil count 3.5 X 10^9/L Platelet count 290 X 10^9/L.Her serum ferritin level was 2.2 mcg/l with normal B12 & folate levels. Hemoglobinopathy screen was normal. Blood film was consistent with iron deficiency. She denied any history of blood loss. In view of positive faecal occult blood, she underwent upper & lower gastrointestinal tract endoscopies which failed to reveal any bleeding lesion. Red cell scan was considered but not arranged as clinically she was not bleeding at a rate more than 1 ml per minute. Capsule enteroscopy was not available. Coeliac screen was negative. Due to intolerance of oral iron supplementation, she needed parenteral iron infusions, which improved her hemoglobin.

However, the response was not sustained which prompted further work up. She underwent bone marrow aspirate & trephine biopsy which was suggestive of mild dyserythropoeisis. Cytogenetics was normal. Hemolytic screen was negative. On immunophenotyping as part of Paroxysmal Nocturnal Hemoglobinuria (PNH) screen, neutrophils showed normal expression of CD 59 (89%)& CD 66b (100%)but completely lacked CD 16 (02%). Urinary haemosiderin was negative. She had no history of increased frequency or of exceptionally severe or persistent infections. Family studies are pending. She remains iron replete on parenteral supplementation.

Conclusion- Polymorphonuclear neutrophils totally deficient in CD16 were detected by chance. CD16 deficiency has not compromised the host defence in this patient. We have not assessed CD16 specific mRNA or functional parameters such as phagocytosis of opsonized bacteria and superoxide production since the patient had no history of increased infections. The other receptors for IgG apparently can compensate for the lack of CD16. Congenital deficiencies of CD16 are very rare. The clinical relevance of congenital defect of neutrophil CD16 expression remains unclear. This case substantiates the inferences of other sporadic reports of there being no compromise of host defence resulting from isolated CD16 neutrophil expression defect.