Neopterin and interferon gamma serum levels in patients with heart and kidney transplants.

The main problem in the follow-up of patients receiving organ allografts is the early differential diagnosis of rejection episodes and infections. Serum levels of interferon gamma, a marker of T-lymphocyte activity, were determined with an immunoradiometric assay, specific for biologically active interferon gamma and sufficiently sensitive (20 U/l) for the determination of circulating interferon gamma. Neopterin, a pteridine released from stimulated macrophages, was determined by radioimmunoassay. Both rejection crises and infections are accompanied by distinct increases of serum neopterin (median values 124 and 128 nmol/l; N = 98). Interferon gamma levels are elevated for a short period one or two days earlier, the maximal values during infections (median 430 U/l, range 120-1220 U/l, N = 25) being higher than those during rejection episodes (median 120 U/l, range less than 20-330 U/l, N = 73). Each rise of interferon gamma was followed by an increase of neopterin, but not every neopterin increase was preceded by a interferon gamma peak. Neither of these parameters showed an increase during deterioration of kidney function due to cyclosporin toxicity. The determination of interferon gamma, a lymphokine involved in the activation of alloreactivity, reflecting T-cell stimulation, and the measurement of neopterin, a secretory product of activated macrophages, allows the simple, quick and reliable monitoring of the immune status of transplant recipients.