This article describes the development and validation of a scintillation proximity assay (SPA) sensitive for guinea-pig
interleukin-5 (IL-5). SPA beads were coated with TRFK-5, a
monoclonal antibody directed against mouse
IL-5, which is known also to bind guinea-pig
IL-5. The assay is a simple competitive binding assay between [125I]-rh-IL-5 and the
IL-5, in a sample of guinea-pig bronchoalveolar lavage fluid (BALF), for the binding site on the TRFK-5-coated beads.
IL-5 levels in BALF ([IL-5]BALF) were shown to increase in guinea-pigs sensitized to
ovalbumin (OvA) and challenged with an OvA inhalation. This occurred at a time (24 h) after challenge when there was also a marked
eosinophilia. The assay was validated by treating guinea-pigs with a second antibody, Genzyme 2374-01, directed against
IL-5. Treatment with this antibody resulted in a significant reduction of the
antigen-induced
eosinophilia and concentration of [IL-5]BALF. This observation confirms that the
IL-5 identified in BALF also cross-reacts with the antibody Genzyme 2374-01. Interestingly, plasma from sensitized, but unchallenged, guinea-pigs also contained detectable levels of
IL-5, and the stimulation of
plasma protein extravasation (PPE) within the airways with inhaled
histamine also induced a rise in [IL-5]BALF. These observations suggest that the plasma may be an additional source of the
IL-5 present in the airways of
antigen-challenged guinea-pigs.