Double diffusion in agarose: precipitin lines which are not the result of antigen--antigody reactions.

Precipitin lines were observed in double diffusion tests between mouse gut tissue homogenates and serum from the same animal. Other tissues failed to produce this result. The line-forming components of the tissue are lipoidal while serum reactants are free of lipid. Purified γ-globulin, IgG, does not react with tissue constituents. An IgM component can be identified as one reactant. Lipopolysaccharides extracted from E. coli 014, Forssman antigen and Kidd—Friedewald antigen could not be demonstrated as reactants. It appears that certain tissue components which may be lipoproteins, and lipid free serum components, one of which is IgM, react in a way which resembles immunological interactions but which are believed not to be so.