Determination of interleukin-2 in cerebrospinal fluid by a sensitive enzyme-linked immunosorbent assay

A sensitive technique was developed for the quantitative detection of intrathecal production of interleukin-2 (IL-2). Concentrations of IL-2 in paired cerebrospinal fluid (CSF) and serum samples were measured by an enzyme-linked immunosorbent assay using a monoclonal antibody and an affinity purified polyclonal antibody. The assay produced a linear response with respect to IL-2 concentration, and could readily detect levels of IL-2 as low as 1.5 international units/ml. Concentrations of IL-2 in CSF and serum samples were standardised by calculating their ratio to albumin concentration in order to correct for passive transudation of IL-2 across blood-CSF barriers. CSF IL-2/albumin ratios higher than concomitant serum ratios were considered indicative of intrathecal IL-2 production. The technique provides a sensitive, specific, and reproducible method for the determination of in vivo synthesis of IL-2 within the central nervous system.