Biomedical subjects

Patrick Skog

Publications and source records attributed to Patrick Skog.

7 recordsLinked to original sources

PubMed2006

Split tolerance in peripheral B cell subsets in mice expressing a low level of Igkappa-reactive ligand.

Peripheral B cell tolerance differs from central tolerance in anatomic location, in the stage of B cell development, and in the diversity of Ag-responsive cells. B cells in secondary lymphoid organs are heterogeneous, including numerous subtypes such as B-1, marginal zone, transitional, and follicular B cells, which likely respond differently from one another to ligand encounter. We showed recently that central B cell tolerance mediated by receptor editing was induced in mice carrying high levels of a ubiquitously expressed kappa-macroself Ag, a synthetic superantigen reactive to Igkappa. In this study, we characterize a new transgenic line that has a distinctly lower expression pattern from those described previously; the B cell tolerance phenotype of these mice is characterized by the presence of significant numbers of immature kappa+ B cells in the spleen, the loss of mature follicular and marginal zone B cells, the persistence of kappa+ B-1 cells in the peritoneal cavity, and significant levels of serum IgM,kappa. These findings suggest distinct signaling thresholds for tolerance among peripheral B cell subsets reactive with an identical ligand.

Animals↗

PubMed2006

Effect of cell:cell competition and BAFF expression on peripheral B cell tolerance and B-1 cell survival in transgenic mice expressing a low level of Igkappa-reactive macroself antigen.

In mice carrying a synthetic Igkappa-reactive superantigen ("kappa macroself antigen"), low level expression induced split peripheral B cell tolerance in the sIgkappa+ compartment, with striking reductions in follicular and marginal zone (MZ) B cells and the retention of significant numbers of sIgkappa+ B-1a but not B-1b cells in the peritoneum. Here, we characterize the transgenic line pKkappa with this split tolerance phenotype and assess the effects of B cell competition and the survival cytokine BAFF (B cell activating factor belonging to the TNF family) on peripheral tolerance. In pKkappa mice the surviving peritoneal and splenic kappa+ B cells were largely lost in mice carrying one copy of the human Ckappa exon in place of the mouse version, a maneuver that generates additional antigen non-reactive competitor B cells in this model. Furthermore, overexpression of BAFF suppressed kappa-macroself antigen-induced deletion and promoted production of both IgM,kappa and IgA,kappa antibodies in mice with normal Igkappa alleles but not in mice carrying one copy of the human Ckappa allele. These findings suggest that BAFF overexpression has minimal effects on the survival of autoreactive B cells in a polyclonal immune system and that B cell:B cell competition plays a potent role in suppressing the survival of B-1 and splenic B cells with excessive autoreactivity.

Animals↗

PubMed2005

deltaBAFF, a splice isoform of BAFF, opposes full-length BAFF activity in vivo in transgenic mouse models.

DeltaBAFF is a novel splicing isoform of the regulator B cell-activating factor (BAFF, BLyS), a TNF family protein with powerful immunoregulatory effects. Overexpression of BAFF leads to excessive B cell accumulation, activation, autoantibodies, and lupus-like disease, whereas an absence of BAFF causes peripheral B cell immunodeficiency. Based on the ability of DeltaBAFF to multimerize with full-length BAFF and to limit BAFF proteolytic shedding from the cell surface, we previously proposed a role for DeltaBAFF in restraining the effects of BAFF and in regulating B lymphocyte homeostasis. To test these ideas we generated mice transgenic for DeltaBAFF under the control of human CD68 regulatory elements, which target expression to myeloid and dendritic cells. We also generated in parallel BAFF transgenic mice using the same expression elements. Analysis of the transgenic mice revealed that DeltaBAFF and BAFF had opposing effects on B cell survival and marginal zone B cell numbers. DeltaBAFF transgenic mice had reduced B cell numbers and T cell-dependent Ab responses, but normal preimmune serum Ig levels. In contrast, BAFF transgenic mice had extraordinarily elevated Ig levels and increases in subsets of B cells. Unexpectedly, both BAFF and DeltaBAFF appeared to modulate the numbers of B-1 phenotype B cells.

Alternative Splicing↗

PubMed2005

An immunoglobulin C kappa-reactive single chain antibody fusion protein induces tolerance through receptor editing in a normal polyclonal immune system.

Understanding immune tolerance mechanisms is a major goal of immunology research, but mechanistic studies have generally required the use of mouse models carrying untargeted or targeted antigen receptor transgenes, which distort lymphocyte development and therefore preclude analysis of a truly normal immune system. Here we demonstrate an advance in in vivo analysis of immune tolerance that overcomes these shortcomings. We show that custom superantigens generated by single chain antibody technology permit the study of tolerance in a normal, polyclonal immune system. In the present study we generated a membrane-tethered anti-Igkappa-reactive single chain antibody chimeric gene and expressed it as a transgene in mice. B cell tolerance was directly characterized in the transgenic mice and in radiation bone marrow chimeras in which ligand-bearing mice served as recipients of nontransgenic cells. We find that the ubiquitously expressed, Igkappa-reactive ligand induces efficient B cell tolerance primarily or exclusively by receptor editing. We also demonstrate the unique advantages of our model in the genetic and cellular analysis of immune tolerance.

Animals↗

PubMed2005

A role for nuclear factor kappa B/rel transcription factors in the regulation of the recombinase activator genes.

In developing B cells, expression of surface immunoglobulin is an important signal to terminate recombinase activator gene (RAG) expression and V(D)J recombination. However, autoreactive antigen receptors instead promote continued gene rearrangement and receptor editing. The regulation by B cell receptor (BCR) signaling of RAG expression and editing is poorly understood. We report that in editing-competent cells BCR ligand-induced RAG mRNA expression is regulated at the level of RAG transcription, rather than mRNA stability. In immature B cells carrying innocuous receptors, RAG expression appears to be under rapidly reversible negative regulation. Studies involving transduction of a superrepressive (sr) I kappa B alpha protein indicate that NF-kappaB/Rel proteins promote RAG transcription. Interestingly, NF kappa B1-deficient cells overexpress RAG and undergo an exaggerated receptor editing response. Our data implicate NF kappa B transcription factors in the BCR-mediated regulation of RAG locus transcription. Rapidly activated NF kappa B pathways may facilitate prompt antigen receptor-regulated changes in RAG expression important for editing and haplotype exclusion.

Animals↗

PubMed2004

Tolerance-induced receptor selection: scope, sensitivity, locus specificity, and relationship to lymphocyte-positive selection.

Receptor editing is a mode of immunological tolerance of B lymphocytes that involves antigen-induced B-cell receptor signaling and consequent secondary immunoglobulin light chain gene recombination. This ongoing rearrangement often changes B-cell specificity for antigen, rendering the cell non-autoreactive and sparing it from deletion. We currently believe that tolerance-induced editing is limited to early stages in B-cell development and that it is a major mechanism of tolerance, with a low-affinity threshold and the potential to take place in virtually every developing B cell. The present review highlights the contributions from our laboratory over several years to elucidate these features.

Animals↗

PubMed2004

Peripheral B lymphocyte tolerance.

This lecture discusses two interrelated topics, B cell tolerance in the peripheral immune system and BAFF. Using the 3-83 antibody transgenic mouse bred to mice carrying cognate antigen in the liver, we previously found that clonal elimination drastically reduced the precursor frequency of autoreactive cells. The consensus model to explain this tolerance is the 2-signal hypothesis, which proposes that in the absence of T cell help BCR stimulation is a negative signal for B cells. However, this model fails to explain how these same B cells can respond to T-independent type II (TI-2) antigens, raising the question of how they distinguish TI-2 antigens from multimeric self determinants. We propose that B cells use NK-like missing self recognition to provide the needed specificity, as foreign antigens are unlikely to carry self markers. The model has implications for the evolution of the immune system, B lymphocyte signaling, tissue specificity of autoimmunity, and microbial subversion of the immune system. Overexpression of the critical B cell survival cytokine BAFF/BLyS has been associated with autoimmunity. We have discovered a novel splice isoform that regulates BAFF activity and may play a role in limiting B cell activity. The novel form, called DBAFF, is able to heteromultimerize with normal BAFF and can suppress receptor binding and proteolytic release from the cell surface. Preliminary studies from transgenic mice overexpressing wild type or DBAFF are consistent with a possible regulatory role for DBAFF, raising the possibility that the relative expression levels of BAFF and DBAFF regulates tolerance.

Animals↗