On a key postulate of T-cell receptor restrictive function: the V-gene loci act as a single pool encoding recognition of the polymorphic alleles of the species major histocompatibility complex

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.

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.

Ten experiments that would make a difference in understanding immune mechanisms

Jacques Monod used to say, "Never trust an experiment that is not supported by a good theory." Theory or conceptualization permits us to put order or structure into a vast amount of data in a way that increases understanding. Validly competing theories are most useful when they make testably disprovable predictions. Illustrating the theory-experiment interaction is the goal of this exercise. Stated bleakly, the answers derived from the theory-based experiments described here would impact dramatically on how we understand immune behavior.

On the logic of restrictive recognition of peptide by the T-cell antigen receptor

This essay provides an analysis of the inadequacy of the current view of restrictive recognition of peptide by the T-cell antigen receptor. A competing model is developed, and the experimental evidence for the prevailing model is reinterpreted in the new framework. The goal is to contrast the two models with respect to their consistency, coverage of the data, explanatory power, and predictability.

Why rethink the structure-function relationships regulating TCR behavior?

Although the generally accepted (Standard) Model of the TCR has powered the accumulation of a large body of crucial data, it is lacking because of the failure of its basic tenet that allele-specific recognition of MHC-encoded restricting elements can be derived by somatic selection on a random repertoire. The limitations of the Standard Model due to this tenet and a glimpse at what a competing model might look like add up to yield a surprising new view of the structure-function relationships of the TCR. A published experiment illustrating this is discussed.

A hypothesis accounting for the paradoxical expression of the D gene segment in the BCR and the TCR

The D gene segment expressed in both the TCR and the BCR has a challenging behavior that begs interpretation. It is incorporated in three reading frames in the rearranged transcription unit but is expressed in antigen-selected cells in a preferred frame. Why was it so important to waste 2/3 of newborn cells? The hypothesis is presented that the D region is framework playing a role in both the TCR and the BCR by determining whether a signal is transmitted to the cell upon interaction with a cognate ligand. This assumption operates in determining haplotype exclusion for the BCR and in regulating the signaling orientation for the TCR. Relevant data as well as a definitive experiment challenging the validity of this hypothesis, are discussed.

What does the T-cell receptor recognize when it docks on an MHC-encoded restricting element?

The postulate is analyzed that single V-gene segments encode recognition of the allele-specific determinants (a) required for the restrictive response of the alphabeta TCR to peptide. The consequence of this is that the positively selected V-domain, Valpha or Vbeta, engages an allele-specific determinant (a) on one subunit or domain of the MHC-encoded restricting element. The entrained V-domain docks on an invariant determinant (i) on the complementing subunit or domain. Consequently, each functional V-domain expresses an anti-a site and an anti-i site, and all subunits or domains of MHC-encoded restricting elements express an a- and i-determinant. The evidence, both biological and structural, discussed here strongly supports this postulate which has far reaching consequences.