Oxazolone-specific cytophilic antibodies in the sera of non-immune CBA mice and mice contact-sensitized with oxazolone, were studied with a rosette test employing peritoneal exudate macrophages and oxazolone-coupled sheep erythrocytes. Macrophage rosettes, produced by direct or indirect cytophilic antibodies, were found to depend on optimally hapten-coupled erythrocytes. Sera obtained 1 week after contact sensitization with oxazolone contained principally 7S IgG2a cytophilic antibodies. Monomeric 7S IgM antibodies cytophilic for macrophages may have been present as well. Primary contact sensitization and boosting was found uniquely to lead to high titres of hyperimmune oxazolone cytophilic antibodies predominantly binding to trypsin-sensitive macrophage receptors.
It has been previously shown that specifically sensitized macrophages mediate a component of delayed skin reactions in mice contact sensitized with oxazolone. Since these reactions can be transferred by immune serum or by normal macrophages coated with immune serum, and since acquisition of this passive sensitization can be abolished by prior trypsinization of these cells, it is suggested that 7S IgG2a and/or 7S IgM cytophilic oxazolone antibodies attaching to trypsin-sensitive macrophage receptors, mediate the specific macrophage component of contact sensitivity in mice.