To provide an updated overview of anti-citrullinated protein antibodies (ACPAs) in rheumatoid arthritis (RA), focusing on (i) how ACPAs are generated, (ii) key mechanisms linking ACPAs to inflammation and bone destruction, and (iii) current and emerging clinical applications and ACPA-related targeted therapeutic prospects, while acknowledging that mechanistic gaps and ACPA subtype diversity remain major challenges for translation.

This work is a narrative review that synthesizes published evidence on citrullination biology, ACPA formation, pathogenic pathways, diagnostic/prognostic utility, and therapeutic strategies in ACPA-positive RA. The approach is consistent with a literature-based overview in which authors collected references and summarized recent progress in diagnosis, disease evaluation, and targeted therapy, rather than reporting new experimental or clinical data.

Generation & heterogeneity: PAD-mediated citrullination and inflammatory stimuli contribute to ACPA emergence; ACPAs are heterogeneous with multiple antigen specificities/subtypes, complicating “one-target-fits-all” approaches.

Pathogenesis (“two-hit” concept and antibody features): ACPA development/maturation can be conceptualized in stages (“hits”); antibody glycosylation/sialylation modulates biological activity and pathogenicity.

Bone/joint damage mechanisms: ACPAs contribute directly/indirectly to inflammation and bone destruction via immune effector pathways (e.g., immune complexes, osteoclast activation, inflammatory cytokine milieu).

Clinical application: ACPAs have high specificity and are used for RA classification/early diagnosis and prognostication (e.g., erosive risk); however, ACPA titers may not reliably mirror disease activity in all settings.

Therapeutic prospects: Multiple ACPA-related strategies are discussed (e.g., anti-citrullination/PAD inhibition, vaccines such as dendritic-cell–based approaches, B-cell–directed strategies, and ACPA-targeting/neutralizing concepts), but efficacy may vary across ACPA subtypes and remains an active area of study. 

ACPAs are central to RA as both clinically useful biomarkers and mechanistic contributors to joint/bone pathology. The field is advancing rapidly in diagnosis, response prediction concepts, and immunotherapeutic innovation; however, substantial heterogeneity across ACPA antigens and isotypes limits “single-target” strategies and may partly explain inconsistent or controversial effects across studies. Continued mechanistic dissection and appropriately designed clinical trials are expected to drive new breakthroughs in understanding ACPA generation, refining clinical deployment, and developing effective ACPA-oriented therapies for ACPA positive RA.