Induction of delayed-type hypersensitivity with BCG-associated proteins.

Microgram quantities of bovine serum albumin (BSA) and hen egg albumin (OA) associate spontaneously with living BCG in aqueous suspension. The association is stable insofar as bound protein cannot be readily dissociated from the organism by repeated washing. Association of BSA or OA is dependent upon the concentration of specific protein or competing protein in the incubation mixture, pH and the amount of protein already bound to the organisms. Washed BCG "complexes" containing either BSA or OA are potent inducers of delayed-type hypersensitivity (DTH). The same soluble proteins are far less effective inducers of DTH, even when injected with BCG. The capacity of OA-BCG complexes to provoke a cell-mediated response seems to be related, at least in part, to "stabilization" of the antigen on an appropriate carrier and its concentration at the site of BCG injection.