Fig 1. Viral enhancement of hapten drugs (amoxicillin):
Hapten drugs like amoxicillin bind by covalent bonds to many proteins in the peripheral blood/tissue, and drug-modified peptides enter the HLA-class I and class II antigen presentation pathway. Nevertheless, no immune response to the modified proteins is developed, probably because co-stimulatory signals, necessary for mounting an immune response, are missing.
A viral infection enhances the expression of immune receptors (TCR, HLA) and costimulatory molecules (e.g., CD80, CD86, CD40).
When the patient is treated with a hapten drug like amoxicillin during such a viral stimulation, the same cell presenting viral peptides may also present amoxicillin-modified peptides in the context of costimulatory molecules. Thus, not only viral-specific T cells are activated, but also amoxicillin-specific T cells, as the costimulation serves both virus and amoxicillin reactions. Immunity to virus and amoxicillin means DH can develop.