Isolated late cutaneous skin test response to ampicillin: a distinct entity.

A case presentation describes a young woman with a history of two reactions to ampicillin therapy and a reproducible skin test reaction of intermediate timing that disappeared within 48 hours. The skin test response was to ampicillin only and not to other penicillin-related skin test reagents. Tests for serum IgE and IgG antibody to ampicillin were negative. The histology was that of a mononuclear and neutrophilic cellular infiltrate with neutrophil margination in the vessels. There was no immunoglobulin, complement, or fibrin deposition. The skin test reaction began and ended earlier than would be expected for a classic delayed hypersensitivity reaction. It is considered to be an isolated late cutaneous response but cannot yet be designated a late cutaneous allergic response. Reactants characteristic of an Arthus reaction were not present, and no alternative immunologic basis was confirmed.