Although the primary function of the DNA mismatch repair (MMR) system is to identify and correct base mismatches that have been erroneously introduced during DNA replication, recent studies have further implicated several MMR components in somatic hypermutation of immunoglobulin (Ig) genes. We studied the immune response in mice deficient in MutS homologue (MSH)3 and MSH6, two mutually exclusive partners of MSH2 that have not been examined previously for their role in Ig hypermutation. In Msh6−/− and Msh3−/−/Msh6−/− mice, base substitutions are preferentially targeted to G and C nucleotides and to an RGYW hot spot, as has been shown previously in Msh2−/− mice. In contrast, Msh3−/− mice show no differences from their littermate controls. These findings indicate that the MSH2–MSH6 heterodimer, but not the MSH2–MSH3 complex, is responsible for modulating Ig hypermutation.

Objective To better define the immunologic character of the T cell infiltrate in lupus nephritis. Methods We performed double immunohistochemical staining and clonotypic T cell receptor (TCR) beta-chain sequencing in multiple anatomic regions isolated by laser-capture microdissection from renal biopsies. Results SLE kidneys have a variably patterned and often extensive infiltrate of predominantly clonally expanded T cells of CD4 and CD8 lineages. CD4 T cells were prominent in nearly two-thirds of SLE biopsies, and distributed as broad periglomerular aggregates or intermixed with CD8 T cells forming periglomerular caps. Sequencing of the T cell TCR from periglomerular regions showed a predominance of clonally expanded T cells. The CD8 T cells, which were present in all biopsies, often adhered to Bowman's capsule and infiltrated the tubular epithelium. They exhibited features that suggest participation in an adaptive immune response: differentiation into CD28null memory-effector phenotype, trafficking of the same expanded clonotype to different regions of the kidney and to the peripheral blood, and clonal persistence for years in repeat biopsies. CD8 T cell tubulitis was especially associated with progressive changes. Conclusions The immunological characteristics of the infiltrating CD4 and CD8 T cells in the lupus kidney indicate they have the potential to mediate injury, which may be relevant to development of progressive renal failure. Whereas the oligoclonality of the CD4 T cell infiltrate is consistent with the paradigm of SLE as a class II-associated autoimmune disease, the finding of CD8 T cell clonality and trafficking implies participation in a distinct systemic adaptive immune response.

We sought to delineate further the immunological significance of T lymphocytes infiltrating the valve leaflets in calcific aortic stenosis (CAS) and determine whether there were associated alterations in circulating T cells. Using clonotypic TCR β-chain length and sequence analysis we confirmed the repertoire of tricuspid CAS valves contains numerous expanded T cell clones with varying degrees of additional polyclonality, which was greatest in cases with severe calcification. We now report a similar proportion of clonal expansions in the much younger bicuspid valve CAS cases. Peripheral blood flow cytometry revealed elevations in HLA-DR+ activated CD8 cells and in the CD8+CD28nullCD57+ memory-effector subset that were significantly greater in both bicuspid and tricuspid CAS cases with more severe valve calcification. Lesser increases of CD4+CD28null T cells were identified, principally in cases with concurrent atherosclerotic disease. Upon immunostaining the CD8 T cells in all valves were mainly CD28null, and CD8 T cell percentages were greatest in valves with oligoclonal repertoires. T cell clones identified by their clonotypic sequence as expanded in the valve were also found expanded in the circulating blood CD28nullCD8+ T cells and to a lesser degree in the CD8+CD28+ subset, directly supporting the relationship between immunologic events in the blood and the valve. The results suggest that an ongoing systemic adaptive immune response is occurring in cases with bicuspid and tricuspid CAS, involving circulating CD8 T cell activation, clonal expansion and differentiation to a memory-effector phenotype, with trafficking of T cells in expanded clones between blood and the valve.

Autoimmune diseases occur when the immune response is targeted to self-antigens, leading to destruction or altered function of specific cells and tissues. Although the aetiology of these diseases has not yet been fully elucidated, it is believed that genetically determined susceptibility and environmental triggers are both implicated in the detrimental immune response against the body's own tissues. Dendritic cells (DCs) are professional antigen presenting cells that play an important role in maintaining peripheral tolerance by preventing self-reactive T cells from causing autoimmune damage. Thus, alterations in the physiology of DCs are likely to be responsible for defective immune regulatory mechanisms and incomplete tolerance to self. Here, we will focus specifically on the ways in which the immunological synapse occurring at the DC-T cell interface can fine-tune the balance between tolerance and immunity and how alterations of this synapse can determine induction or perpetuation of autoimmune responses. Activating/inhibitory receptors expressed on the surface of DCs and T cells modulate the function of these cells and influence the course of the immune response. Pharmacological approaches that can modulate DC function will be also addressed as a potential antigen-specific strategy in the design of new, noninvasive therapies to prevent or to treat chronic inflammatory autoimmune disorders.

hypermutation, suggesting that cis-acting sequences outside the mutable region regulate and target mutation. However, almost nothing is known about the detailed molecular mechanisms or trans-acting proteins that are responsible for V-region hypermutation.