Vδ2 T cell deficiency in granulomatosis with polyangiitis (Wegener's granulomatosis)

Tissue-Resident Immune Cells in Humans

Tissue-resident immune cells span both myeloid and lymphoid cell lineages, have been found in multiple human tissues, and play integral roles at all stages of the immune response, from maintaining homeostasis to responding to infectious challenges to resolution of inflammation to tissue repair. In humans, studying immune cells and responses in tissues is challenging, although recent advances in sampling and high-dimensional profiling have provided new insights into the ontogeny, maintenance, and functional role of tissue-resident immune cells. Each tissue contains a specific complement of resident immune cells. Moreover, resident immune cells for each lineage share core properties, along with tissue-specific adaptations. Here we propose a five-point checklist for defining resident immune cell types in humans and describe the currently known features of resident immune cells, their mechanisms of development, and their putative functional roles within various human organs. We also consider these aspects of resident immune cells in the context of future studies and therapeutics.

Pathogenetic and Clinical Aspects of Anti-Neutrophil Cytoplasmic Autoantibody-Associated Vasculitides

Anti-neutrophil cytoplasmic autoantibodies (ANCA) targeting proteinase 3 (PR3) and myeloperoxidase expressed by innate immune cells (neutrophils and monocytes) are salient diagnostic and pathogenic features of small vessel vasculitis, comprising granulomatosis with polyangiitis (GPA), microscopic polyangiitis, and eosinophilic GPA. Genetic studies suggest that ANCA-associated vasculitides (AAV) constitute separate diseases, which share common immunological and pathological features, but are otherwise heterogeneous. The successful therapeutic use of anti-CD20 antibodies emphasizes the prominent role of ANCA and possibly other autoantibodies in the pathogenesis of AAV. However, to elucidate causal effects in AAV, a better understanding of the complex interplay leading to the emergence of B lymphocytes that produce pathogenic ANCA remains a challenge. Different scenarios seem possible; e.g., the break of tolerance induced by a shift from non-pathogenic toward pathogenic autoantigen epitopes in inflamed tissue. This review gives a brief overview on current knowledge about genetic and epigenetic factors, barrier dysfunction and chronic non-resolving inflammation, necro-inflammatory auto-amplification of cellular death and inflammation, altered autoantigen presentation, alternative complement pathway activation, alterations within peripheral and inflamed tissue-residing T- and B-cell populations, ectopic lymphoid tissue neoformation, the characterization of PR3-specific T-cells, properties of ANCA, links between autoimmune disease and infection-triggered pathology, and animal models in AAV.

[Effector memory T‑cells in the pathogenesis of ANCA-associated vasculitides. German version]

Patients with antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides (AAV) have an expansion of effector memory T‑cells in peripheral blood. The enlarged effector memory cell population contains distinct cell subsets, including T‑helper type 1 (Th1) CD4+ T‑cells lacking co-stimulatory CD28 expression and Th17 cells in granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) and Th2 type and Th17 cells in eosinophilic granulomatosis with polyangiitis (EGPA). The cytokine response of autoreactive proteinase 3 (PR3)-specific effector memory T‑cells is skewed towards an increase of Th2 type, Th17 and Th22 cell fractions in GPA. Anomalous effector memory CD4+ T‑cell co-stimulation is suggested by the aberrant expression of P‑selectin glycoprotein ligand‑1, beta‑2 integrin, chemokine receptors, natural-killer group 2 member D (NKG2D) and other activating receptors. The increased expression of these receptors is accompanied by T‑cell activation and migration to inflamed tissues. The T‑cells are abundant and secrete proinflammatory cytokines in inflammatory lesions in AAV. The T‑cell mediated tissue damage correlates with renal outcome, whereas B-cell infiltration does not. Activation of lesional CD4+NKG2D+ effector memory T‑cells is independent of the antigen; moreover, CD4+NKG2D+ effector memory T‑cells display NK-cell-like cytotoxicity towards microvascular endothelial cells in vitro. Thus, effector memory T‑cells play an important role in tissue damage and disease progression in AAV. Sequentially administered or combined with B-cell depleting therapy, T‑cell-directed therapies, especially those directed against effector memory CD4+ T‑cells, may further improve the outcome and help to achieve long-term remission in AAV.

Effector memory T‑cells in the pathogenesis of ANCA-associated vasculitides

Patients with antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides (AAV) have an expansion of effector memory T‑cells in peripheral blood. The enlarged effector memory cell population contains distinct cell subsets, including T‑helper type 1 (Th1) CD4⁺ T‑cells lacking co-stimulatory CD28 expression and Th17 cells in granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) and Th2 type and Th17 cells in eosinophilic granulomatosis with polyangiitis (EGPA). The cytokine response of autoreactive proteinase 3 (PR3)-specific effector memory T‑cells is skewed towards an increase of Th2 type, Th17, and Th22 cell fractions in GPA. Anomalous effector memory CD4⁺ T‑cell co-stimulation is suggested by the aberrant expression of P‑selectin glycoprotein ligand-1, β‑2 integrin, chemokine receptors, natural-killer group 2 member D (NKG2D) and other activating receptors. The increased expression of these receptors is accompanied by T‑cell activation and migration to inflamed tissues. T‑cells are abundant and secrete proinflammatory cytokines in inflammatory lesions in AAV. The T‑cell mediated tissue damage correlates with renal outcome, whereas B‑cell infiltration does not. Activation of lesional CD4⁺NKG2D⁺ effector memory T‑cells is independent of the antigen; moreover, CD4⁺NKG2D⁺ effector memory T‑cells display NK-cell-like cytotoxicity towards microvascular endothelial cells in vitro. Thus, effector memory T‑cells play an important role in tissue damage and disease progression in AAV. Sequentially administered or combined with B‑cell depleting therapy, T‑cell-directed therapies, especially those directed against effector memory CD4⁺ T‑cells, may further improve the outcome and help to achieve long-term remissions in AAV.

Inhibition of human γδ T cell proliferation and effector functions by neutrophil serine proteases

Human peripheral blood γδ T cells expressing the Vγ9Vδ2 T cell receptor are activated by microbial or endogenous pyrophosphate antigens and indirectly by nitrogen-containing bisphosphonates. Apart from proliferation, such phosphoantigens induce proinflammatory cytokine production including TNF-α and IFN-γ and trigger cytotoxic effector function. Neutrophil granulocytes are known to modulate T cell activation. The neutrophil serine proteases proteinase 3, elastase and cathepsin G have multiple potential targets and promote microbial killing. In this study, we investigated the effect of the three serine proteases on the in vitro proliferation and effector functions of γδ T cells cultured in serum-free medium. All three proteases inhibited the proliferative activity, suppressed the cytokine production and decreased the cytotoxicity of γδ T cells. Further studies indicated that proteolytic cleavage of IL-2 and modulation of butyrophilin 3A1 (CD277) expression might contribute to the overall inhibition.