Limitations of neutrophil depletion by anti-Ly6G antibodies in two heterogenic immunological models.

Neutrophil-depleting antibodies, such as anti-GR1 (RB6-8C5) and anti-Ly6G (1A8), are commonly used to study the in vivo function of neutrophils in murine disease models. Anti-Ly6G antibodies became the standard, because in contrast to anti-GR1, these do not bind Ly6C. The efficiency of the depletion needs to be carefully analysed as flow cytometry plots may be misinterpreted. For example, the staining intensity of GR1 on neutrophils (CD11b+ GR1hi) drops upon anti-Ly6G administration. We show that this drop is due to competition between anti-GR1 and anti-Ly6G antibodies. Neutrophil depletion with anti-Ly6G in naive mice was organ- and strain-specific. Furthermore, an incomplete anti-Ly6G-dependent neutrophil depletion was obtained in two immune-mediated mouse models, i.e. in malaria-infected C57BL/6 mice and in complete Freund's adjuvant (CFA)-challenged BALB/c mice. BrdU-incorporation studies show a slight increase in proliferating bone marrow neutrophils upon depletion in naive mice. Strikingly, depletion with anti-Ly6G in CFA-challenged BALB/c mice resulted in a significant increase in proliferating splenic neutrophils, causing a fast rebound of new immature neutrophils. In conclusion, our results emphasize the importance of careful panel design, gating strategies and duration of neutrophil depletion and highlight the context-dependent Ly6G depletion efficiency. It furthermore underlines the need for new tools to understand the in vivo role of neutrophils in immunological models.