Neopterin

Neopterin is a pteridine derivative produced mainly by activated macrophages and dendritic cells in response to stimulation by interferon-gamma, a cytokine released by activated T cells. It serves as a biomarker of cellular immune system activation and is released into the bloodstream and excreted in urine.

Biosynthesis occurs in immune cells from guanosine triphosphate (GTP) via the GTP cyclohydrolase I pathway. The process reflects macrophage activation during Th1-type immune responses and is not predominantly associated with a direct antimicrobial function, but rather indicates immune system engagement.

Clinically, elevated neopterin levels indicate immune activation and are observed in a range of conditions, including acute and chronic infections (notably viral infections), autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus, inflammatory disorders, various cancers, and after organ transplantation. Urinary and serum neopterin measurements can aid in assessing disease activity, monitoring treatment response, or evaluating immune status, though the marker is not disease-specific.

Measurement methods typically involve high-performance liquid chromatography with fluorometric detection or immunoassays. Neopterin levels can be influenced by renal function, age, and concurrent inflammatory states, so results are interpreted in the clinical context and often in conjunction with other laboratory tests.

Neopterin is valued in clinical practice as a relatively stable indicator of cellular immune activation. Its interpretation relies on understanding the patient’s overall clinical picture, as elevations are non-specific and reflect generalized immune system engagement rather than a single disease process.