Immunologic features of penicillin sensitivity in patients with the four major forms of clinical allergic reactions to penicillin and in appropriate control subjects have been studied. The clearest picture in terms of mechanism is available for the immediate (including anaphylactic) and serum sickness types of reactions. Both of these appear to be mediated by circulating skin-sensitizing antibodies. Among the delayed clinical reactions, maculopapular eruptions in some instances are associated with delayed skin test reactions to penicillin. The evidence suggesting a possible mitigating effect of circulating IgG antibodies in delayed penicillin sensitivity and the observed occurrence of desensitization following exposure to a large dose of penicillin indicates that the mechanism in these reactions is complex.
Fellner MJ. An Immunologic Study of Selected Penicillin Reactions Involving the Skin. Arch Dermatol. 1968;97(5):503-519. doi:10.1001/archderm.1968.01610110011002