Paul M. Allen, Ph.D.

Robert L. Kroc Professor
Pathology and Immunology

Immunology Program

  • 314-362-8758

  • 314-747-2046

  • 314-362-8888

  • 8118

  • 8607 BJCIH


  • alloreactivity, autoimmunity, immunological synapse, major histocompatibility complex, rheumatoid arthritis, T cells

  • Recognition of antigen by T cells

Research Abstract:

The fate and function of T cells is mediated by the T cell receptor (TCR) recognizing a peptide/MHC complex on the surface of an antigen presenting cell. This critical recognition event is highly specific, but paradoxically relatively low affinity. The research in our laboratory is centered upon elucidating how the TCR recognizes antigen, and its relationship to the development and function of T cells. There are four major focus areas: the Hb(64-76)/I-Ek antigen system, a murine model of rheumatoid arthritis, alloreactivity, and self-peptides and positive selection of T cells.

We have developed and extensively characterized a model antigen system based on the Hb(64-76)/I-Ek epitope. This system includes TCR transgenic mice, a series of ligands with defined affinities, transgenic mice expressing the ligands as neo-self antigens, and crystal structures. From studies using these reagents we have been able to define kinetic thresholds for T cell development and tolerance in the thymus and explored the function of the co-receptor molecule, CD4. Using the Hb(64-76)/I-Ek, we have also visualized and quantified the formation of the immunological synapse, a critical structure formed between a T cell and an APC. Using a novel yeast display system, we are now performing directed evolution of TCRs, making them higher affinity and/or with changed specificity, and then determining what functional, structural, and biophysical changes have occurred. We are also exploring the role of key signaling molecules in T cell development and activation, including Ca2++, PLC-theta, and L-plastin. These studies with the Hb(64-76)/I-Ek will provide new insights into how the fascinating TCR recognizes antigen.

The immune system is normally tolerant to self-antigens; however, failure to do so can result in autoimmunity. We utilize a murine model of rheumatoid arthritis (K/BxN) in which transgenic CD4 T cells provide help to B cells in the generation of autoantibodies against glucose 6-phosphate isomerse (GPI)resulting in an inflammatory process similar to human rheumatoid arthritis. The inflammation is joint specific disease, despite GPI being a ubiquitously expressed self protein. Using micro positron emission tomography (microPET), we have shown that the antibodies within 7 minutes specifically localized to the affected joints. We have further delineated the stages involved in the development of arthritis, showing that the localization depended upon mast cells, neutrophils, Fc Receptors, immune complexes, but not C5. We are now investigating how the GPI autoantigen is localized to the joints, and what products of the neutrophils and mast cells are essential for disease induction. To study B cell tolerance in this model, we have generated anti-GPI IgG transgenic mice and found that MZ B cells are spontaneously activated whereas, LN B cells require T cell help. We have developed a chronic transfer model, based on the KRN system, which permits being able to definitely assess how, when, and where are T cells involved in the initiation,maintenance of chronic arthritis, and interactions with monocytes and neutrophils.

Alloreactivity is the ability of a T cell to recognize foreign MHC molecules, to which the T cell had never been exposed, and is observed in vivo as graft rejection, graft versus host disease, and in vitro by a mixed lymphocyte reaction (MLR). The phenomenon of alloreactivity has been known for a long time; however, the precise molecular basis for it is yet to be fully defined. Using a large scale T cell and peptide screening approach, we identified naturally processed allopeptides identified by 9 I-Ek alloreactive T cells. Three of these T cells recognized multiple distinct peptides, which shared no sequence homology. The alloreactive T cells recognized each pMHC specifically, and utilized a distinct constellation of I-Ek contact residues for each interaction. These studies make the novel finding that each alloreacti ve T cell has a germline encoded capacity to recognize multiple distinct ligands, thereby displaying polyspecificity, not degeneracy. These findings provide an explanation for the high frequency of alloreactivity.

Self-peptides are an integral part of the development and maintenance of T cells, which we have determined to be in the mM affinity range. We are exploring the nature of the peptides that are involved in these interactions by utilizing a large self-peptide library we have identified by mass spectrometry of I-Ek bound peptides. The identity and specificity of the peptides that are involved in positive selection of thymocytes and co-agonist activity of mature T cells, will help us elucidate how T cells can productively interact with these low affinity, but essential, ligands.

Selected Publications:

Persaud SP, Donermeyer DL, Weber KS, Kranz DM, Allen PM. High-affinity T cell receptors differentiates cognate peptide-MHC and altered peptide ligands with distinct kinetics and thermodynamics. Mol Immunol. 2010 May;47(9):1793-801. Epub 2010 Mar 23.

Felix NJ, Donermeyer DL, Horvath S, Walters JJ, Gross ML, Suri A, Allen PM. Alloreactive T cells specifically recognize multiple distinct peptide/MHC ligands. Nat Immunol 2007 8:388-397.

Donermeyer DL, Weber KS, Kranz DM, Allen PM. The study of high-affinity TCRs reveals duality in T cell recognition of antigen: Specificity and degeneracy. J Immunol 2006 177:6911-6919.

Mandik-Nayak L, Racz JL, Sleckman BP, Allen PM. Autoreactive MZ B cells are spontaneously activated but LN B cells require T cell help. J Exp Med 2006 203:1985-1998.

Kao H, Allen PM. An antagonist peptide mediates positive selection and CD4 lineage commitment of MHC class II-restricted T cells in the absence of CD4. J Exp Med 2005 201:149-158.

Last Updated: 8/3/2011 1:00:09 PM

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