Neutrophils are vital for proper immune function and without them, the body is vulnerable to the development of life-threatening infections. Neutrophils are required in large numbers, but their lifespan is short meaning they need to be constantly replaced. To ensure the body is equipped with enough of these cells, a complex network of regulators are crucial for the on-going production of these cells. One important pathway utilises the granulocyte colony-stimulating factor receptor (G-CSFR), which is involved in the differentiation and proliferation of neutrophil precursors into mature neutrophils but can also influence their function.
Mutations have been found in the G-CSFR than can contribute to a variety of illnesses, including acute myeloid leukemia (AML), a cancer characterised by an abnormal number of immature white blood cells in the bone marrow. In AML, especially that preceded by congenital neutropenia, the mutations are found in the intracellular portion of G-CSFR. This leads to sustained activation but with altered downstream signalling, resulting in enhanced proliferation but reduced maturation. However, where these mutations also impact the function of the neutrophils produced has not been studied.
This study used a zebrafish mpx:GFP transgenic line with green fluorescent neutrophils containing a truncating G-CSFR mutation mimicking that seen in AML, introduced by genome editing, with non-edited fish as a control (‘wild-type’). Neutrophil numbers were determined by counting GFP+ cells, while neutrophil function was assessed by infection with E. coli expressing Turbo RFP (red fluorescence) and assaying the number of RFP+ bacteria and GFP+ neutrophils. Preliminary data indicated both mutant and wildtype groups responded to bacterial infection with increased neutrophil numbers, with equivalent clearing of E.coli. This suggests the neutrophils produced by the truncated mutant G-CSFR are functional.