“Allorestriction” should be distinguished from “alloreactivity”

The case for allele-specific recognition by the TCR

There is a sharp difference in how one views TCR structure-function-behaviour dependent on whether its recognition of major histocompatibility complex-encoded restriction elements (R) is germline selected or somatically generated. The generally accepted or Standard model is built on the assumption that recognition of R is by the V regions of the αβ TCR, which is not driven by allele specificity, whereas the competing model posits that recognition of R is allele-specific. The establishing of allele-specific recognition of R by the TCR would rule out the Standard model and clear the road to a consideration of a competing construct, the Tritope model. Here, the case for allele-specific recognition (germline selected) is detailed making it obvious that the Standard model is untenable.

TCR-pMHC interactions: Two peptide repertoires-one signal

The peptide (P) ligand seen by the TCR is presented by an MHC-encoded restricting element (R). Peptide is viewed from two perspectives, that of the TCR and that of R. The TCR looks at P using an anti-P site that is somatically generated and selected, whereas R looks at P using a binding site that is germline generated and selected. The two segments of P, the one viewed by the TCR, the other viewed by R divide P into two repertoires, Ptcr and Pr that are recognized independently but function cooperatively. The consequences of this for an understanding of TCR specificity and signalling as well as the role of differential processing are analysed. It is ironic that from the point of view of the immunologist, the TCR is highly polyreactive recognizing over a million peptides, whereas from the point of view of the immune system, the TCR is highly specific recognizing essentially only one epitope.

Signaling interactions predicted by the Tritope model of the TCR

As the data accumulates, it becomes obvious that the Standard Model of TCR structure-function relationships is in jeopardy. The proposed Tritope model has become more meaningful and, in any case, is richer in prediction and explanation. This is illustrated here by using the signaling interactions of the TCR as examples. An unsuspected signaling pathway for positive selection, and for alloreactivity, is predicted. Further, crucial data needed to elucidate the structural elements that distinguish signaling for restrictive- versus allo-reactivity are identified.

Core principles characterizing immune function

The immune system is an anticipatory mechanism designed by evolution to protect the individual against noxious agents and harmful cellular debris. In order to recognize substances that it has never encountered, the immune system somatically generates an appropriately sized random (with respect to self and nonself [NS]) recognitive repertoire that is coupled to a biodestructive and ridding output. Consequently, a Self-NS discrimination is required in order to avoid autoimmunity. This essay is an attempt to highlight the core principles upon which this anticipatory mechanism depends in order to function.

Contemplating Bretscher's View that the Tritope Model is 'Implausible'

There is, at present, only two models of the TCR structure-function relationship. These are referred to here as the Standard (Centric) model and the Tritope model. While I have argued that the Standard model is untenable and proposed the Tritope to replace it, Bretscher has argued that the Tritope model is 'implausible' and throws his support for the Standard model. This essay analyses the implausibility argument concluding that it is unfounded.

Challenging the Tritope Model of T cell receptor structure-function relationships with classical data on 'super' and 'allo-MHC' antigens

The response of the immune system to allo-MHC-encoded antigens and Mls 'superantigens' has been experimentally analysed in detail, but the data have not been coupled to a theoretical framework. It should therefore be instructive to see how well the newly proposed Tritope Model of TCR structure-function relationships deals with the signalling interactions between the TCR and the above antigens. We will pay heed to William Bateson's admonition, 'treasure the exceptions', by showing how a meaningful theory interrogates the data with the same validity that the data interrogate the theory. The concordances, as well as the contradictions, with the Tritope Model are a test of its heuristic value.