Secukinumab (Cosentyx) is a fully human IgG1κ antibody that selectively neutralizes IL-17A. Ixekizumab (Taltz) is a humanized IgG4 antibody that also selectively neutralizes IL-17A but with higher binding affinity. Bimekizumab (Bimzelx) is a humanized IgG1 bispecific-like antibody that neutralizes both IL-17A and IL-17F, providing broader IL-17 pathway blockade. Clinical data suggest Bimekizumab achieves higher skin clearance rates in psoriasis, possibly due to dual IL-17A/F neutralization.

IL-17A and IL-17F share ~55% sequence homology and signal through the same IL-17RA/RC receptor complex. However, IL-17A homodimers are 10-30× more potent than IL-17F homodimers in inducing pro-inflammatory gene expression. The IL-17A/F heterodimer has intermediate potency. IL-17F may play a more significant role in mucosal immunity and host defense against certain infections. For drug development, testing candidate antibodies against all three forms (IL-17A, IL-17F, IL-17A/F) clarifies the neutralization breadth.

The standard assay uses HT-29 (human colon adenocarcinoma) or human foreskin fibroblast (HFF) cells stimulated with IL-17A. After 24 hours, measure IL-6 or IL-8 (CXCL8) secretion in the supernatant by ELISA. To test neutralization, pre-incubate IL-17A with serial dilutions of the candidate anti-IL-17A antibody (30-60 min, 37°C) before adding to cells. A potent neutralizing antibody should show dose-dependent inhibition of IL-6/IL-8 production with an IC₅₀ in the low nanomolar range.

IL-17A is a secreted cytokine, so intracellular staining is required. Stimulate PBMCs with PMA + Ionomycin for 4-6 hours in the presence of a protein transport inhibitor (Brefeldin A or Monensin). Surface-stain for CD3, CD4, then fix, permeabilize, and stain with a fluorochrome-conjugated anti-IL-17A antibody (PE recommended). Gate on live CD3⁺CD4⁺ cells and identify the IL-17A⁺ population as Th17 cells. Include an isotype control or FMO control for accurate gating.

IL-17A plays a critical role in mucosal host defense against extracellular bacteria and fungi — particularly Candida albicans and Staphylococcus aureus. Patients receiving anti-IL-17A therapy have an elevated risk of mucocutaneous candidiasis (oral and esophageal thrush). This is a known class effect of IL-17 pathway blockade. In preclinical studies, Candida infection models are used to evaluate the infection risk profile of anti-IL-17 candidates.