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Figure 1 | World Allergy Organization Journal

Figure 1

From: The p-i Concept: Pharmacological Interaction of Drugs With Immune Receptors

Figure 1

The p-i concept. A schematic representation of the p-i concept in comparison with the hapten concept. A, In the p-i concept, the drug (eg, SMX) binds to the TCR and provides some initial signal. In most instances, this signal is insufficient to induce T-cell activation with cytokine synthesis and proliferation. The signal is strengthened by the additional interaction with HLA molecules. It seems to be rather independent of the type of peptide embedded and sometimes even from the HLA allele. Drug binding and HLA interactions stimulate T cells like a normal peptide/HLA complex. Because this way of T-cell stimulation does not follow the rules of the development of a normal immune response, the subsequent activations appear clinically and upon in vitro analysis often chaotic and uncoordinated. B, In the hapten hypothesis, the hapten-modified peptide is recognized and stimulates T cells. The hapten may also have the ability to activate the innate immune system, for example, dendritic cells.

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