A two-particle turbidometric latex immunoassay for the detection of specific IgM antibodies.

A simple two stage assay using latex particles as a reaction indicator has been developed for the detection of IgM antibodies to Trichinella spiralis. In the first stage, magnetic polystyrene beads (Dynabeads) coated with T. spiralis antigen were incubated for 30 min with the test serum. After washing, in the second stage, the assay was developed for 1 h using anti-mu-coated latex particles. After sedimentation of the Dynabeads the turbidity of the resultant latex suspension was measured spectrophotometrically at a wavelength of 400 nm. A decrease in turbidity of more than 20% from that of the control, unreacted, suspension was considered positive. Using an IgM phosphorylcholine-binding monoclonal antibody which was reactive with T. spiralis, the sensitivity of the assay was determined to be 110 ng/ml of antibody. This was 20-fold less than the sensitivity achieved in an indirect enzyme-linked immunosorbent assay (ELISA). When the assay was applied to sera obtained from CBA/N or BALB/c mice, which were either normal or immunized against T. spiralis, the expected results were obtained with titers up to 1/640 observed, and confirmed (r = 0.93, P less than 0.001) in the ELISA.