Attributes of gammadelta intraepithelial lymphocytes as suggested by their transcriptional profile.

gammadelta T lymphocytes in the intestinal intraepithelial layer (gammadelta IELs) are thought to contribute to immune competence, but their actual function remains poorly understood. Here we used DNA microarrays to study the gene expression profile of gammadelta IELs in a Yersinia infection system to better define their roles. To validate this approach, mesenteric lymph node CD8(+) alphabeta T cells were similarly analyzed. The transcription profiles show that, whereas lymph node CD8(+) alphabeta T cells must be activated to become cytotoxic effectors, gammadelta IELs are constitutively activated and appear to use different signaling cascades. Our data suggest that gammadelta IELs may respond efficiently to a broad range of pathological situations irrespective of their diverse T cell antigen receptor repertoire. gammadelta IELs may modulate local immune responses and participate in intestinal lipid metabolism, cholesterol homeostasis, and physiology. This study provides a strong basis for further investigations of the roles of these cells as well as mucosal immune defense in general.

A genomic view of immunology.

The outstanding problems facing immunology are whole system issues: curing allergic and autoimmune disease and developing vaccines to stimulate stronger immune responses against pathogenic organisms and cancer. We hope that the human genome sequence will reveal the molecular checks and balances that ensure both an effective immunogenic response against pathogenic microorganisms and a suitably tolerogenic response to self antigens and innocuous environmental antigens. Three synergistic approaches--sequence homology searches, messenger RNA expression profiling on microarrays, and mutagenesis in mice--provide the best opportunities to reveal, in the genome sequence, key proteins and pathways for targeting by new immunomodulatory treatments.

A population of murine gammadelta T cells that recognize an inducible MHC class Ib molecule.

Although gammadelta T cells are implicated in regulating immune responses, gammadelta T cell-ligand pairs that could mediate such regulatory functions have not been identified. Here, the expression of the major histocompatibility complex (MHC) class Ib T22 and the closely related T10 molecules is shown to be activation-induced, and they confer specificity to about 0.4% of the gammadelta T cells in normal mice. Thus, the increased expression of T22 and/or T10 might trigger immunoregulatory gammadelta T cells during immune responses. Furthermore, the fast on-rates and slow off-rates that characterize this receptor/ligand interaction would compensate for the low ligand stability and suggest a high threshold for gammadelta T cell activation.

Induction of rapid T cell activation and tolerance by systemic presentation of an orally administered antigen.

To understand how orally introduced antigen regulates peripheral immune responses, we fed cytochrome c protein to mice transgenic for the beta chain of a cytochrome c-specific TCR and followed the antigen-specific T cell responses with a cyt c/I-Ek tetramer staining reagent. We find that within 6 hr of cytochrome c administration, antigen-specific systemic T cell activation is induced, and spleen cells gain the ability to stimulate cytochrome c-specific T cell responses. Feeding multiple low doses of cytochrome c down-regulates the systemic immune response, which can be correlated with a reduction of antigen-specific T cells and not with immune deviation. These results suggest that systemic distribution of antigen contributes significantly to oral tolerance induction.

Analysis of the requirements for class II-restricted T cell recognition of a single determinant reveals considerable diversity in the T cell response and degeneracy of peptide binding to I-Ed.

The amino acid sequences recognized by five I-E(d)-restricted and one E alpha A beta d-restricted murine T cell clones were determined. The clones had been raised to a synthetic peptide representing amino acids 305-328 of influenza virus hemagglutinin. It was found that although all of the T cell clones recognized a single 10-residue region of the peptide, 307KYVKQNTLKL316, different clones could recognize minimal ("core") determinants spanning 8, 9, or 10 of these amino acids. To see whether particular amino acids within the sequence 307-316 were universally important for T cell recognition, the six clones were assayed for their ability to tolerate single amino acid substitutions of the 10 residue peptide. In all, 190 analogues of the peptide in which each amino acid in the sequence was replaced, in turn, by each of the other 19 naturally occurring amino acids were tested. It was shown that 1) the six T cell clones had very different requirements for recognition of the peptide, 2) substitutions at every single position within the peptide could be shown to affect recognition in a T cell-specific manner, and 3) every single position within the peptide could be replaced by a large number of amino acids and still be recognized by at least one T cell clone. These results demonstrate the great diversity exhibited by the T cell repertoire in recognizing a 10-amino acid determinant, as well as the degeneracy of peptide binding to I-E(d).