Induction of CD4 T cell changes in murine AIDS is dependent on costimulation and involves a dysregulation of homeostasis

Homeostatic proliferation of mature T cells

Under normal circumstances, the secondary lymphoid tissues contain a predictable number of T cells with a diverse T cell receptor (TCR) repertoire. Such a T cell pool must be of sufficient size to confer maximum protection of the host from infectious pathogens and cancer, but small enough not to overburden the host. The T cell pool is maintained by a combination of de novo T cell production by the thymus and by the long-term survival and gradual turnover of mature T cells in the periphery. The latter process, termed homeostatic proliferation, has been intensely investigated over the past 20 years, and a few techniques have been developed to facilitate these studies. In this chapter, we describe the experimental procedures that allow conspicuous visualization of homeostatic proliferation, which have been instrumental in facilitating recent advances in the study of T cell homeostasis.

Influence of surface topography on osteoblast response to fibronectin coated calcium phosphate thin films

The ability to engineer biomaterial surfaces that are capable of a dynamic interaction with cells and tissues is central to the development of medical implants with improved functionality. An important consideration in this regard is the role played by the extracellular proteins that bind to an implant surface in vivo. Deliberate use of an ad-layer of such proteins on an implant surface has been observed to guide and direct cell response. However, the role that changes in surface topography might play in determining the nature of this cell-protein-surface interaction has not been investigated in detail. In this study, calcium phosphate (CaP) thin films have been deposited onto substrates with varying topography such that this is reflected in the (conformal) CaP surface features. A fibronectin (FN) ad-layer was then deposited from solution onto each surface and the response of MG63 osteoblast-like cells investigated. The results revealed that in all cases, the presence of the adsorbed FN layer on the CaP thin films improved MG63 cell adhesion, proliferation and promoted early onset differentiation. Moreover, the nature and scale of the response were shown to be influenced by the underlying CaP surface topography. Specifically, MG63 cell on FN-coated CaP thin films with regular topographical features in the nanometer range showed statistically significant differences in focal adhesion assembly, osteocalcin expression and alkaline phosphase activity compared to CaP thin films that lacked these topographical features. As such, these data indicate that surface topography can be used to further influence cell adhesion and downstream differentiation by enhancing the effects of a surface adsorbed FN layer.

T cell-intrinsic role of Nod2 in promoting type 1 immunity to Toxoplasma gondii

Nod2 belongs to the (NOD)-like receptor (NLR) family of proteins, which function as intracellular pathogen sensors in innate immune cells. Nod2-deficiency results in an impaired immune response against bacterial pathogens. However, our understanding of how this protein promotes host defense against intracellular parasites is unknown. Here we found that Nod2^−/− mice showed reduced clearance of Toxoplasma gondii and decreased interferon-γ production. Reconstitution of T-cell deficient mice with Nod2^−/− T cells followed by T. gondii infection revealed a T cell-intrinsic defect. Nod2^−/− CD4⁺ T cells displayed poor helper T cell differentiation, which was associated with impaired IL-2 production and nuclear accumulation of c-Rel. These data revealed a T cell-intrinsic role of Nod2 signaling that is critical for host defense against T. gondii.

The role of CD4 T cells in the pathogenesis of murine AIDS

LP-BM5, a retroviral isolate, induces a disease featuring retrovirus-induced immunodeficiency, designated murine AIDS (MAIDS). Many of the features of the LP-BM5-induced syndrome are shared with human immunodeficiency virus-induced disease. For example, CD4 T cells are critical to the development of MAIDS. In vivo depletion of CD4 T cells before LP-BM5 infection rendered genetically susceptible B6 mice MAIDS resistant. Similarly, MAIDS did not develop in B6.nude mice. However, if reconstituted with CD4 T cells, B6.nude mice develop full-blown MAIDS. Our laboratory has shown that the interaction of B and CD4 T cells that is central to MAIDS pathogenesis requires ligation of CD154 on CD4 T cells with CD40 on B cells. However, it is not clear which additional characteristics of the phenotypically and functionally heterogeneous CD4 T-cell compartment are required. Here, in vivo adoptive transfer experiments using B6.nude recipients are employed to compare the pathogenic abilities of CD4 T-cell subsets defined on the basis of cell surface phenotypic or functional differences. Th1 and Th2 CD4 T cells equally supported MAIDS induction. The rare Thy1.2(-) CD4 subset that expands upon LP-BM5 infection was not necessary for MAIDS. Interestingly, CD45RB(low) CD4 T cells supported significantly less disease than CD45RB(high) CD4 T cells. Because the decreased MAIDS pathogenesis could not be attributed to inhibition by CD45RB(low) CD25(+) natural T-regulatory cells, an intrinsic property of the CD45RB(low) cells appeared responsible. Similarly, there was no evidence that natural T-regulatory cells played a role in LP-BM5-induced pathogenesis in the context of the intact CD4 T-cell population.

A role for T lymphocytes in mediating cardiac diastolic function

The induction of T helper (TH) lymphocytes by distinct TH ligands results in a differentiation to TH1/TH2 subsets based on their unique pattern of cytokine secretion and effector functions. We hypothesized that the relative proportion of TH1/TH2 directly relates to cardiac fibroblast (CF) function and thereby cardiac extracellular matrix (ECM) composition and cardiac diastolic function in the absence of injury or altered wall stress. We compared the effect of selective TH1 with TH2 inducers on cardiac gene expression, ECM composition, and diastolic function in C57BL/J mice. Twelve weeks after immune modulation, the left ventricular stiffness (beta) was significantly increased in the TH1 group and decreased in the TH2 group (P < 0.01). The TH2 group also demonstrated significantly increased end-diastolic and end-systolic volumes (P < 0.01). Cardiac gene expression patterns for pro-matrix metalloproteinase (MMP)-9 and -13 were increased by greater than fivefold in the TH2 group and significantly decreased in the TH1 group (P < 0.05). The total cardiac collagen and cross-linked collagen were significantly increased in the TH1 group and decreased in the TH2 group (P < 0.01). Coculturing lymphocytes harvested from the treated mice with naive primary CF demonstrated a direct control of the lymphocytes on CF pro-collagen, pro-MMP gene expression, and MMP activity. These results suggest that the TH phenotype differentially affects diastolic function through modulating CF pro-collagen and pro-MMP gene expression, MMP activity, and cardiac collagen cross-linking, resulting in altered ECM composition. Thus modulation of TH lymphocyte function could promote adaptive remodeling in heart failure and postmyocardial infarction.