InVivoMAb anti-mouse/human VLA-4 (CD49d)

Recent studies have shown that the quantity of donor-reactive memory T cells is an important factor in determining the relative heterologous immunity barrier posed during transplantation. Here, we hypothesized that the quality of T cell memory also potently influences the response to costimulation blockade-based immunosuppression. Using a murine skin graft model of CD8+ memory T cell-mediated costimulation blockade resistance, we elicited donor-reactive memory T cells using three distinct types of pathogen infections. Strikingly, we observed differential efficacy of a costimulation and integrin blockade regimen based on the type of pathogen used to elicit the donor-reactive memory T cell response. Intriguingly, the most immunosuppression-sensitive memory T cell populations were composed primarily of central memory cells that possessed greater recall potential, exhibited a less differentiated phenotype, and contained more multi-cytokine producers. These data, therefore, demonstrate that the memory T cell barrier is dependent on the specific type of pathogen infection via which the donor-reactive memory T cells are elicited, and suggest that the immune stimulation history of a given transplant patient may profoundly influence the relative barrier posed by heterologous immunity during transplantation.

Integrin-ligand interactions between germinal center (GC) B cells and Ag-presenting follicular dendritic cells (FDCs) have been suggested to play central roles during GC responses, but their in vivo requirement has not been directly tested. In this study, we show that, whereas integrins alphaLbeta2 and alpha4beta1 are highly expressed and functional on mouse GC B cells, removal of single integrins or their ligands had little effect on B cell participation in the GC response. Combined beta2 integrin deficiency and alpha4 integrin blockade also did not affect the GC response against a particulate Ag. However, the combined integrin deficiency did cause B cells to be outcompeted in splenic GC responses against a soluble protein Ag and in mesenteric lymph node GC responses against gut-derived Ags. Similar findings were made for beta2-deficient B cells in mice lacking VCAM1 on FDCs. The reduced fitness of the GC B cells did not appear to be due to decreased Ag acquisition, proliferation rates, or pAKT levels. In summary, our findings provide evidence that alphaLbeta2 and alpha4beta1 play overlapping and context-dependent roles in supporting interactions with FDCs that can augment the fitness of responding GC B cells. We also find that mouse GC B cells upregulate alphavbeta3 and adhere to vitronectin and milk-fat globule epidermal growth factor VIII protein. Integrin beta3-deficient B cells contributed in a slightly exaggerated manner to GC responses, suggesting this integrin has a regulatory function in GC B cells.

Effector CD8(+) T cells (CD8 TE) play a key role during hepatotropic viral infections. Here, we used advanced imaging in mouse models of hepatitis B virus (HBV) pathogenesis to understand the mechanisms whereby these cells home to the liver, recognize antigens, and deploy effector functions. We show that circulating CD8 TE arrest within liver sinusoids by docking onto platelets previously adhered to sinusoidal hyaluronan via CD44. After the initial arrest, CD8 TE actively crawl along liver sinusoids and probe sub-sinusoidal hepatocytes for the presence of antigens by extending cytoplasmic protrusions through endothelial fenestrae. Hepatocellular antigen recognition triggers effector functions in a diapedesis-independent manner and is inhibited by the processes of sinusoidal defenestration and capillarization that characterize liver fibrosis. These findings reveal the dynamic behavior whereby CD8 TE control hepatotropic pathogens and suggest how liver fibrosis might reduce CD8 TE immune surveillance toward infected or transformed hepatocytes.

Selection of the primary antibody repertoire takes place in pro-/pre-B cells, and subsequently in immature and transitional B cells. At the first checkpoint, mu heavy (muH) chains assemble with surrogate light (SL) chain into a precursor B-cell receptor. In mice lacking SL chain, muH chain selection is impaired, and serum autoantibody levels are elevated. However, whether the development of autoantibody-producing cells is due to an inability of the resultant B-cell receptors to induce central and/or peripheral B-cell tolerance or other factors is unknown. Here, we show that receptor editing is defective, and that a higher proportion of BM immature B cells are prone to undergoing apoptosis. Furthermore, transitional B cells are also more prone to undergoing apoptosis, with a stronger selection pressure to enter the follicular B-cell pool. Those that enter the marginal zone (MZ) B-cell pool escape selection and survive, possibly due to the B-lymphopenia and elevated levels of B-cell activating factor. Moreover, the MZ B cells are responsible for the elevated IgM anti-dsDNA antibody levels detected in these mice. Thus, the SL chain is required for central and peripheral B-cell tolerance and inhibits anti-DNA antibody production by MZ B cells.