Available online 6 March 2024, 113652

Streptococcus pyogenes infections require alternative strategies due to antibiotic resistance.

Flow cytometry-based method with THP-1 cells efficiently assesses FcγR-mediated phagocytosis driven by antibodies targeting Streptococcus pyogenes.

The test's accuracy and limits are confirmed and validated for testing human sera.

Streptococcus pyogenes, commonly referred to as Group A Streptococcus (Strep A), causes a spectrum of diseases, with the potential to progress into life-threatening illnesses and autoimmune complications. The escalating threat of antimicrobial resistance, stemming from the prevalent reliance on antibiotic therapies to manage Strep A infections, underscores the critical need for the development of disease control strategies centred around vaccination. Phagocytes play a critical role in controlling Strep A infections, and phagocytosis-replicating assays are essential for vaccine development. Traditionally, such assays have employed whole-blood killing or opsonophagocytic methods using HL-60 cells as neutrophil surrogates. However, assays mimicking FcγR- phagocytosis in clinical contexts are lacking. Therefore, here we introduce a flow cytometry-based method employing undifferentiated THP-1 cells as monocytic/macrophage model to swiftly evaluate the ability of human sera to induce phagocytosis of Strep A. We extensively characterize the assay's precision, linearity, and quantification limit, ensuring robustness. By testing human pooled serum, the assay proved to be suitable for the comparison of human sera's phagocytic capability against Strep A. This method offers a valuable complementary assay for clinical studies, addressing the gap in assessing FcγR-mediated phagocytosis. By facilitating efficient evaluation of Strep A -phagocyte interactions, it may contribute to elucidating the mechanisms required for the prevention of infections and inform the development of future vaccines and therapeutic advancements against Strep A infections.

Streptococcus pyogenes

Strep A

THP-1 cells

Opsonophagocytosis

Flow cytometry

Half Effective Concentration

Fluorescein isothiocyanate

Human Leukemia 60 (cell line)

Intravenous Immunoglobulin

Limit of Quantification

Multiplicity of infection

Opsonophagocytic killing assay

Rheumatic heart disease

Group A Streptococcus

(human monocytic cell line)

© 2024 The Authors. Published by Elsevier B.V.