Urinary neopterin in infants with primary immunodeficiency.

Neopterin is produced in large amounts specifically from macrophages upon stimulation with interferon-gamma (IFN-gamma). Measurement of neopterin allows a direct in vivo quantification of T cell activation. This is particularly useful, e.g., in early diagnosis of graft rejection. Since disease states with elevated neopterin levels in some cases are coupled with an impaired cellular immunity, we decided to investigate the possible influence that severely diminished cellular immunity might have on urinary neopterin levels. Our investigation on six children with severe primary immunodeficiency presents some evidence that immunodeficiency itself does not account for an increase in neopterin when patients are free from infections. Neopterin was also normal in an SCID patient who was completely lacking T cells and was suffering from severe infections. Two patients with primary immunodeficiency and residual T lymphocytes suffered from severe infections and showed elevated neopterin. The data support the hypothesis that elevated neopterin levels are dependent on the presence of activated T lymphocytes. Residual T lymphocytes of SCID patients have the capacity to induce neopterin in vivo when patients suffer from infections.