The Dual Role of the Classical Complement Pathway: From Immunoprotection and Immunopathology to Clinical Applications Applications: A Narrative Review

Background: The classical complement pathway is a key component of the innate immune system, playing a critical role in host defense against pathogens and malignant cells. However, its dysregulation can lead to significant immunopathological conditions.


Objectives: This narrative review aims to explore the dual role of the classical complement pathway in both immunoprotection and hypersensitivity reactions, as well as its clinical applications.


Methods: This review was conducted through a comprehensive analysis of previously published literature retrieved from major scientific databases, including PubMed, Scopus, and Google Scholar. Relevant studies were selected based on their scientific quality, relevance to the topic, and recency.


Results: The findings demonstrate that activation of the classical pathway contributes to immune defense through mechanisms such as complement-dependent cytotoxicity, opsonization, and inflammation. Conversely, excessive or uncontrolled activation is implicated in various hypersensitivity reactions, including hemolytic anemia, Arthus reaction, serum sickness, and autoimmune diseases such as rheumatoid arthritis. Furthermore, the complement system has important clinical applications in immunodiagnostic techniques, such as complement fixation tests, and in immunotherapy, particularly through monoclonal antibody-mediated cancer treatment.


Conclusion: the classical complement pathway exhibits a dual role in maintaining immune balance, acting as both a protective mechanism and a contributor to disease pathology. Understanding this balance is essential for the development of targeted diagnostic and therapeutic strategies.