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Background: Neutrophils have been shown to contribute to the pathophysiology of hidradenitis suppurativa (HS), a chronic, painful and debilitating inflammatory skin disease, yet their exact role remains to be fully defined. Granulocyte colony-stimulating factor (G-CSF), a major regulator of neutrophil development and survival, can be blocked by the novel, fully human anti-G-CSF receptor (G-CSFR) monoclonal antibody CSL324., Objectives: We investigated the activation and migration of neutrophils in HS and the impact of blocking G-CSFR with CSL324., Methods: Biopsy and peripheral blood samples were taken from participants of two studies: 2018.206, a noninterventional research study of systemic and dermal neutrophils and inflammatory markers in patients with neutrophilic skin diseases, and CSL324&#95;1001 (ACTRN12616000846426), a single-dose ascending and repeated dose, randomized, double-blind, placebo-controlled study to assess the safety, pharmacokinetics and pharmacodynamics of CSL324 in healthy adult subjects. Ex vivo experiments were performed, including neutrophil enumeration and immunophenotyping, migration, receptor occupancy and transcriptome analysis., Results: The number of cells positive for the neutrophil markers myeloperoxidase (MPO) and neutrophil elastase (NE) was significantly higher in HS lesions compared with biopsies from healthy donors (HDs) (P < 0.0001 and P = 0.0223, respectively). In peripheral blood samples, mean neutrophil counts were significantly higher in patients with HS than in HDs (2.98 vs. 1.60 × 109 L-1, respectively; P = 8.8 × 10-4). Neutrophil migration pathways in peripheral blood were increased in patients with HS and their neutrophils demonstrated an increased migration phenotype, with higher mean CXCR1 on the surface of neutrophils in patients with HS (24453.20 vs. 20798.47 for HD; P = 0.03). G-CSF was a key driver of the transcriptomic changes in the peripheral blood of patients with HS and was elevated in serum from patients with HS compared with HDs (mean 6.61 vs. 3.84 pg mL-1, respectively; P = 0.013). Administration of CSL324 inhibited G-CSF-induced transcriptional changes in HDs, similar to those observed in the HS cohort, as highlighted by expression changes in genes related to neutrophil migratory capacity., Conclusions: Data suggest that neutrophils contribute to HS pathophysiology and that neutrophils are increased in lesions due to an increase in G-CSF-driven migration. CSL324 counteracted G-CSF-induced transcriptomic changes and blocked neutrophil migration by reducing cell-surface levels of chemokine receptors., Competing Interests: Conflicts of interest C.G., A.B., K.S.-I., B.S., M.A., E.G., L.T., C.M., A.D., M.N., N.W., J.F. and L.M.L. were all working for CSL Innovation at the time of manuscript preparation. J.S.K.: related to this work: grants to institution for advisory board and trial design-related consulting and safety review committee participation and conducting of clinical trials from CSL; unrelated to this work: grants to institution for advisory board and trial design-related consulting work from Boehringer, Sanofi and UCB; grants to institution for conducting of clinical trial from AbbVie, Amgen, Amryt, Argenix, Astra-Zeneca, BMS, Boehringer, Dermira, Eli-Lilly, Exopharm, Galderma, Novartis, Pfizer, Regeneron, Sanofi and UCB Biopharma; Board Director nonremunerated Skin Health Institute, Carlton, VIC; Board Member Australasian Society of Dermatologic Research., (© The Author(s) 2023. Published by Oxford University Press on behalf of British Association of Dermatologists.)