Efforts to identify antibodies to γ-d-glutamyl polypeptide in sera from rabbits injected with encapsulated cells of Bacillus anthracis were unsuccessful. Antisera to a variety of antigens unrelated to B. anthracis, as well as sera from rabbits injected with B. anthracis, contained basic proteins which reacted with the polypeptide when tested by the usual serologic techniques including the precipitin, agar diffusion, and complement fixation reactions. The nonspecific reactions occurred most strongly in water and decreased in sensitivity with increasing concentrations of NaCl. Positive reactions were also given by all these techniques when egg white lysozyme was substituted for antiserum. DNA precipitated most of the material in serum that reacted with polypeptide and similarly, polypeptide precipitated the material that reacted with DNA. The complexes formed between DNA and serum proteins or egg white lysozyme also fixed complement.
Most of the serum protein that reacted with γ-D-glutamyl polypeptide could be removed by adsorbing on Bentonite. The amount of nonspecific protein precipitable with γ-d-glutamyl polypeptide increased in serum following injection of a variety of antigens. Serum lysozyme is believed to account for part of the nonspecific protein.
The use of egg white lysozyme conjugated with fluorescent dye for staining encapsulated cells of B. anthracis is described. The reaction with egg white lysozyme can be used for the rapid detection of low concentrations of glutamyl polypeptide.