The line blot: an immunoassay for monoclonal and other antibodies. Its application to the serotyping of gram-negative bacteria.

A procedure is described for assaying antibodies based on the application of antigen to nitrocellulose as a line with an ink pen point. The method requires no expensive apparatus, is easy to perform, and requires less than 0.25 micrograms of antigen per assay. More than 45 antigens can be assayed simultaneously with a single antibody. Antigens can be applied as purified proteins, extracts, or sodium dodecyl sulfate solubilized extracts. The application of the line blot assay for the detection of monoclonal antibodies which recognize heat-sensitive and insensitive epitopes on the typhus rickettsia surface protein antigen is described. A new serotyping assay for Gram-negative bacteria is also described in which sodium dodecyl sulfate solubilized antigens are applied as lines with and without prior proteinase K digestion. The value of the line blot serotyping assay is demonstrated with Proteus. Rickettsia, Rochalimaea, and Legionella antigens. The line blot immunoassay is a simple, but powerful and flexible, alternative to dot and cross-dot immunoassays.