Activation of primary T lymphocytes results in lysosome development and polarized granule exocytosis in CD4+and CD8+subsets, whereas expression of lytic molecules confers cytotoxicity to CD8+T cells

Transcription factor networks drive perforin activity in the anti-bacterial immune response of tilapia

Perforin, produced by natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), is one of the effectors of cell-mediated cytotoxicity (CMC) in vertebrates, playing a paramount role in killing target cells. However, whether and how perforin is involved in adaptive immune responses in early vertebrates remains unclear. Using Nile tilapia (Oreochromis niloticus) as a model, we investigated the characteristics of perforin in early vertebrates. Oreochromis niloticus perforin (OnPRF) possesses 2 conserved functional domains, membrane attack complex/perforin (MACPF) and protein kinase C conserved region 2 (C2) domains, although they share low amino acid sequence similarity with other homologs. OnPRF was widely expressed in various immune tissues and could respond to lymphocyte activation and T-cell activation in vitro at both the transcriptional and protein levels, indicating that it may be involved in adaptive immune responses. Furthermore, after infection with Edwardsiella piscicida and Aeromonas hydrophila, the mRNA and protein levels of OnPRF were significantly up-regulated within the adaptive immune response period. Additionally, we revealed that many transcription factors were involved in the transcriptional regulation of OnPRF, including p65, c-Fos, c-Jun, STAT1 and STAT4, and there was a synergy among these transcription factors. Overall, these findings demonstrate the involvement of OnPRF in T-cell activation and adaptive immune response in tilapia, thus providing new evidence for comprehending the evolution of immune response in early vertebrates.

CD3-engaging bispecific antibodies trigger a paracrine regulated wave of T-cell recruitment for effective tumor killing

The mechanism of action of bispecific antibodies (bsAbs) directing T-cell immunity to solid tumors is incompletely understood. Here, we screened a series of CD3xHER2 bsAbs using extracellular matrix (ECM) embedded breast cancer tumoroid arrays exposed to healthy donor-derived T-cells. An initial phase of random T-cell movement throughout the ECM (day 1-2), was followed by a bsAb-dependent phase of active T-cell recruitment to tumoroids (day 2-4), and tumoroid killing (day 4-6). Low affinity HER2 or CD3 arms were compensated for by increasing bsAb concentrations. Instead, a bsAb binding a membrane proximal HER2 epitope supported tumor killing whereas a bsAb binding a membrane distal epitope did not, despite similar affinities and intra-tumoroid localization of the bsAbs, and efficacy in 2D co-cultures. Initial T-cell-tumor contact through effective bsAbs triggered a wave of subsequent T-cell recruitment. This critical surge of T-cell recruitment was explained by paracrine signaling and preceded a full-scale T-cell tumor attack.

Intra- and Extracellular Effector Vesicles From Human T And NK Cells: Same-Same, but Different?

Cytotoxic T lymphocytes (CTL) and Natural Killer (NK) cells utilize an overlapping effector arsenal for the elimination of target cells. It was initially proposed that all cytotoxic effector proteins are stored in lysosome-related effector vesicles (LREV) termed "secretory lysosomes" as a common storage compartment and are only released into the immunological synapse formed between the effector and target cell. The analysis of enriched LREV, however, revealed an uneven distribution of individual effectors in morphologically distinct vesicular entities. Two major populations of LREV were distinguished based on their protein content and signal requirements for degranulation. Light vesicles carrying FasL and 15 kDa granulysin are released in a PKC-dependent and Ca²⁺-independent manner, whereas dense granules containing perforin, granzymes and 9 kDa granulysin require Ca²⁺-signaling as a hallmark of classical degranulation. Notably, both types of LREV do not only contain the mentioned cytolytic effectors, but also store and transport diverse other immunomodulatory proteins including MHC class I and II, costimulatory and adhesion molecules, enzymes (i.e. CD26/DPP4) or cytokines. Interestingly, the recent analyses of CTL- or NK cell-derived extracellular vesicles (EV) revealed the presence of a related mixture of proteins in microvesicles or exosomes that in fact resemble fingerprints of the cells of origin. This overlapping protein profile indicates a direct relation of intra- and extracellular vesicles. Since EV potentially also interact with cells at distant sites (apart from the IS), they might act as additional effector vesicles or intercellular communicators in a more systemic fashion.

IgE cross-linking induces activation of human and mouse mast cell progenitors

BACKGROUND

The concept of innate and adaptive effector cells that are repleted by maturing inert progenitor cell populations is changing. Mast cells develop from rare mast cell progenitors populating peripheral tissues at homeostatic conditions, or as a result of induced recruitment during inflammatory conditions.

OBJECTIVE

Because FcεRI-expressing mast cell progenitors are the dominating mast cell type during acute allergic lung inflammation in vivo, we hypothesized that they are activated by IgE cross-linking.

METHODS

Mouse peritoneal and human peripheral blood cells were sensitized and stimulated with antigen, or stimulated with anti-IgE, and the mast cell progenitor population analyzed for signs of activation by flow cytometry. Isolated peritoneal mast cell progenitors were studied before and after anti-IgE stimulation at single-cell level by time-lapse fluorescence microscopy. Lung mast cell progenitors were analyzed for their ability to produce IL-13 by intracellular flow cytometry in a mouse model of ovalbumin-induced allergic airway inflammation.

RESULTS

Sensitized mouse peritoneal mast cell progenitors demonstrate increased levels of phosphorylation of tyrosines on intracellular proteins (total tyrosine phosphorylation), and spleen tyrosine kinase (Syk) phosphorylation after antigen exposure. Anti-IgE induced cell surface-associated lysomal-associated membrane protein-1 (LAMP-1) in naive mast cell progenitors, and prompted loss of fluorescence signal and altered morphology of isolated cells loaded with lysotracker. In human mast cell progenitors, anti-IgE increased total tyrosine phosphorylation, cell surface-associated LAMP-1, and CD63. Lung mast cell progenitors from mice with ovalbumin-induced allergic airway inflammation produce IL-13.

CONCLUSIONS

Mast cell progenitors become activated by IgE cross-linking and may contribute to the pathology associated with acute allergic airway inflammation.

Circulating mature granzyme B+ T cells distinguish Crohn's disease-associated axial spondyloarthritis from axial spondyloarthritis and Crohn's disease

BACKGROUND

Axial spondyloarthritis (axSpA) has strong connections with intestinal inflammation as occurs in Crohn's disease (CD). However, the immunologic mechanisms that distinguish axSpA, CD, and those with features of both diseases (CD-axSpA) are unknown. This study aimed to address this question by initial unbiased single cell RNA-sequencing (scRNAseq) on a pilot cohort followed by validating findings using flow cytometry and ELISA in a larger cohort.

METHODS

Two individuals each with CD, axSpA, CD-axSpA, and healthy controls (HC) were recruited for a pilot discovery scRNAseq cohort, and the validation cohort consisted of 18 axSpA, 24 CD, 13 CD-axSpA, and 17 HC that was evaluated by flow cytometry on PBMCs and ELISAs for plasma cytokines.

RESULTS

Uniquely, PBMCs from subjects with CD-axSpA demonstrated a significant increase in granzyme B+ T cells of both CD4+ and CD8+ lineages by both scRNAseq and flow cytometry. T cell maturation was also greater in those with CD-axSpA, particularly the CD4+ granzyme B+ population. Pathway analysis suggested increased interferon response genes in all immune cell populations within CD-axSpA. Although IFN-γ was elevated in the plasma of a subset of subjects with CD-axSpA, IL-6 was also significantly elevated.

CONCLUSIONS

Our findings support the presence of a chronic interferonopathy in subjects with CD-axSpA characterized by interferon signaling by pathway analysis and an expansion of mature, cytotoxic T cells. These data indicate fundamental immunological differences between CD-axSpA and both of the putative "parent" conditions, suggesting that it is a distinct disease with unique natural history and treatment needs.

Lysosome activation in peripheral blood mononuclear cells and prognostic significance of circulating LC3B in COVID-19

Coronavirus disease 2019 (COVID-19) has spread rapidly worldwide, causing significant mortality. There is a mechanistic relationship between intracellular coronavirus replication and deregulated autophagosome–lysosome system. We performed transcriptome analysis of peripheral blood mononuclear cells (PBMCs) from COVID-19 patients and identified the aberrant upregulation of genes in the lysosome pathway. We further determined the capability of two circulating markers, namely microtubule-associated proteins 1A/1B light chain 3B (LC3B) and (p62/SQSTM1) p62, both of which depend on lysosome for degradation, in predicting the emergence of moderate-to-severe disease in COVID-19 patients requiring hospitalization for supplemental oxygen therapy. Logistic regression analyses showed that LC3B was associated with moderate-to-severe COVID-19, independent of age, sex and clinical risk score. A decrease in LC3B concentration <5.5 ng/ml increased the risk of oxygen and ventilatory requirement (adjusted odds ratio: 4.6; 95% CI: 1.1–22.0; P = 0.04). Serum concentrations of p62 in the moderate-to-severe group were significantly lower in patients aged 50 or below. In conclusion, lysosome function is deregulated in PBMCs isolated from COVID-19 patients, and the related biomarker LC3B may serve as a novel tool for stratifying patients with moderate-to-severe COVID-19 from those with asymptomatic or mild disease. COVID-19 patients with a decrease in LC3B concentration <5.5 ng/ml will require early hospital admission for supplemental oxygen therapy and other respiratory support.

Peculiar Phenotypic and Cytotoxic Features of Pulmonary Mucosal CD8 T Cells in People Living with HIV Receiving Long-Term Antiretroviral Therapy

People living with HIV have high burdens of chronic lung disease, lung cancers, and pulmonary infections despite antiretroviral therapy (ART). The rates of tobacco smoking by people living with HIV vastly exceed that of the general population. Furthermore, we showed that HIV can persist within the lung mucosa despite long-term ART. As CD8 T cell cytotoxicity is pivotal for controlling viral infections and eliminating defective cells, we explored the phenotypic and functional features of pulmonary versus peripheral blood CD8 T cells in ART-treated HIV⁺ and uninfected controls. Bronchoalveolar lavage fluid and matched blood were obtained from asymptomatic ART-treated HIV⁺ smokers (n = 11) and nonsmokers (n = 15) and uninfected smokers (n = 7) and nonsmokers (n = 10). CD8 T cell subsets and phenotypes were assessed by flow cytometry. Perforin/granzyme B content, degranulation (CD107a expression), and cytotoxicity against autologous Gag peptide-pulsed CD4 T cells (Annexin V⁺) following in vitro stimulation were assessed. In all groups, pulmonary CD8 T cells were enriched in effector memory subsets compared with blood and displayed higher levels of activation (HLA-DR⁺) and exhaustion (PD1⁺) markers. Significant reductions in proportions of senescent pulmonary CD28^-CD57⁺ CD8 T cells were observed only in HIV⁺ smokers. Pulmonary CD8 T cells showed lower perforin expression ex vivo compared with blood CD8 T cells, with reduced granzyme B expression only in HIV⁺ nonsmokers. Bronchoalveolar lavage CD8 T cells showed significantly less in vitro degranulation and CD4 killing capacity than blood CD8 T cells. Therefore, pulmonary mucosal CD8 T cells are more differentiated, activated, and exhausted, with reduced killing capacity in vitro than blood CD8 T cells, potentially contributing to a suboptimal anti-HIV immune response within the lungs.

The effects of BAFF on T lymphocytes in chronic obstructive pulmonary disease

Background

It has been reported that B cell activating factor belonging to the tumor necrosis factor family (BAFF) expression is increased in chronic obstructive pulmonary disease (COPD). However its role in this chronic inflammatory disease is not fully understood. Previous studies have suggested that BAFF also affects T cell function. We therefore investigated the effects of BAFF on T lymphocytes in COPD.

Methods

BAFF was detected in the cells of sputum and the plasma. Peripheral blood mononuclear cells (PBMCs) were isolated from COPD patients and treated with BAFF or BAFF plus BR3-Fc (BAFF antagonist). The apoptosis of CD4⁺ cells and CD8⁺ cells was analyzed by flow cytometry. CD4⁺ cells and CD8⁺ cells were isolated from peripheral blood of COPD patients respectively and treated with BAFF or BAFF plus BR3-Fc. Interferon-γ (IFN-γ) and interleukin-4 (IL-4) were detected in the CD4⁺ cells, and perforin and granzyme B were detected in the CD8⁺ cells.

Results

BAFF expression was increased in the cells of sputum and the plasma from COPD patients compared with control subjects. The plasma BAFF levels were inversely correlated with FEV₁ percentage of predicted in patients with COPD. BAFF did not significantly alter the apoptosis of CD4⁺ cells, however it significantly inhibited the apoptosis of CD8⁺ cells from COPD patients. BAFF increased IFN-γ expression in the CD4⁺ cells from COPD patients, while it did not significantly alter the expresson of IL-4 in these cells. BAFF increased the expression of perforin and granzyme B in the CD8⁺ cells from COPD patients.

Conclusions

Our findings indicate that BAFF may be involved in the inflammatory response in COPD via affecting T lymphocytes, suggesting a possible role of BAFF in the pathogenesis of COPD.

Cytotoxic Tph-like cells are involved in persistent tissue damage in IgG4-related disease

OBJECTIVES

The aim of this study was to determine pathological features of T peripheral helper (Tph)-like (PD-1⁺CXCR5^-CD4⁺ T) cells in IgG4-related disease (IgG4-RD).

METHODS

Tph-like cells in the blood and submandibular glands (SMGs) from IgG4-RD patients were analyzed by flow cytometry. Correlations between level of a Tph-like cell subset and clinical parameters of IgG4-RD were investigated. The cytotoxic capacity of Tph-like cells was also examined. Expression profiles of a molecule related to a Tph-like cell subset in IgG4-RD SMGs were assessed by immunohistochemistry.

RESULTS

Tph-like cells from IgG4-RD patients highly expressed a fractalkine receptor, CX3CR1. Percentages of circulating CX3CR1⁺ Tph-like cells were significantly correlated with clinical parameters including IgG4-RD Responder Index, number of involved organs, and serum level of soluble IL-2 receptor. CX3CR1⁺ Tph-like cells abundantly possessed cytotoxic T lymphocyte-related molecules such as granzyme A, perforin, and G protein-coupled receptor 56. Functional assays revealed their cytotoxic potential against vascular endothelial cells and ductal epithelial cells. Immunohistochemistry showed that fractalkine was markedly expressed in vascular endothelial cells and ductal epithelial cells in IgG4-RD SMGs.

CONCLUSION

CX3CR1⁺ Tph-like cells are thought to contribute to persistent tissue injury in IgG4-RD and are a potential clinical marker and/or therapeutic target for inhibiting progression of IgG4-RD.

Mechanistic peculiarities of activation-induced mobilization of cytotoxic effector proteins in human T cells

It is widely accepted that cytotoxic T and NK cells store effector proteins including granzymes, perforin and Fas ligand (FasL) in intracellular granules, often referred to as secretory lysosomes. Upon target cell encounter, these organelles are transported to the cytotoxic immunological synapse, where they fuse with the plasma membrane to release the soluble effector molecules and to expose transmembrane proteins including FasL on the cell surface. We previously described two distinct species of secretory vesicles in T and NK cells that differ in size, morphology and protein loading, most strikingly regarding FasL and granzyme B. We now show that the signal requirements for the mobilization of one or the other granule also differ substantially. We report that prestored FasL can be mobilized independent of extracellular Ca2+, whereas the surface exposure of lysosome-associated membrane proteins (Lamps; CD107a and CD63) and the release of granzyme B are calcium-dependent. The use of selective inhibitors of actin dynamics unequivocally points to different transport mechanisms for individual vesicles. While inhibitors of actin polymerization/dynamics inhibit the surface appearance of prestored FasL, they increase the activation-induced mobilization of CD107a, CD63 and granzyme B. In contrast, inhibition of the actin-based motor protein myosin 2a facilitates FasL-, but impairs CD107a-, CD63- and granzyme B mobilization. From our data, we conclude that distinct cytotoxic effector granules are differentially regulated with respect to signaling requirements and transport mechanisms. We suggest that a T cell might 'sense' which effector proteins it needs to mobilize in a given context, thereby increasing efficacy while minimizing collateral damage.

Impact of Pegylated Interferon-alfa-2a on Perforin Level in Patients With Chronic Hepatitis B; Preliminary Study

BACKGROUND

Chronic hepatitis B is one of the most common causes of cirrhosis and hepatocellular toxicity in many countries, including Iran. Cytotoxic T lymphocyte (CTL) and Natural killer (NK) cells are the two of main cell populations considered as cytotoxic cells. One of the distinct pathways CTL and NK cells exert cytotoxicity is perforin/granzyme. After the cytotoxic cell/target cell junction, perforin is released from granules by exocytosis. Once it is anchored, perforin forms cylindrical pores through which granzymes and granulysin enter and induce apoptosis.

OBJECTIVES

Large controlled trials have demonstrated the efficacy of PEG-IFN-α-2a in treatment of chronic hepatitis B. This study was aimed to examine whether the enhancement of cytotoxicity by PEG-IFN-α-2a is mainly due to the perforin pathway.

PATIENTS AND METHODS

This research work was performed on 50 patients and five healthy people. Patients with chronic hepatitis B were further subdivided into two groups: patients with inactive chronic hepatitis B (carriers, n = 30), and those with active chronic hepatitis B who were under treatment with PEG-IFN-alfa-2a (n = 20) for minimum six and maximum 12 months. Serum perforin level was measured using ELISA method (CUSABIO Company), HBV viral load was assessed using COBAS Taq-man, and we used Elecsys hepatitis B surface antigen (HBs Ag) II quantitative assay method for HBs Ag determination. HBeAg was evaluated by ELISA method, and AST and ALT were measured by routine laboratorymethods.

RESULTS

Based on the results obtained serum perforin level in healthy group was 0.64 ng/mL, the mean of serum perforin level in inactive HBs Ag carriers was 2.63ng/mL, and 4.63 ng/mL in patients with active chronic hepatitis B under treatment with PEG-IFN-α-2a. The mean of serum perforin level in patients with and without virologic response to treatment were 5.45 ng/mL,and 3.4 ng/mL respectively. Finally in patients with virologic response and seroconverted serum perforin level was 7.23 ng/mL.

CONCLUSIONS

Based on our results higher perforin level in patients under treatment with PEG-IFN-α-2a, could be an indication of elevated cytotoxicity via perforin/granzyme pathway.

Characterisation of the T cell and dendritic cell repertoire in a murine model of mucopolysaccharidosis I (MPS I)

BACKGROUND

Mucopolysaccharidosis I (MPS I) is a metabolic disorder caused by α-L-Iduronidase (IDUA) deficiency, resulting in lysosomal accumulation of heparan (HS) and dermatan sulphate (DS). This has been reported in microglia, yet currently the effect of IDUA deficiency on T cells and dendritic cells (DC) and their functionality in disease pathogenesis remains unclear.

METHODS

Peripheral blood was collected from 3 month old C57BL/6 MPS I (n = 11) and wildtype (WT) (n = 6) mice. T cell and DC phenotype and functional characteristics were identified by flow cytometry.

RESULTS

MPS I mice exhibited a reduction in DC (p = <0.001) along with CD8+ cytotoxic (p = 0.01) and CD4+ T helper (p = 0.032) cells, compared to WT controls. MPS I DC displayed a significant decrease in cell surface CD123 (p = 0.02) and CD86 (p = 0.006) expression. Furthermore, CD45RB expression was significantly reduced on T helper cells in the MPS I population (p = 0.019).

CONCLUSION

We report a reduction in circulating DC and T cells in the MPS I mouse; indicative of adaptive immune dysfunction. DC reduction may occur in response to down-regulation of the IL-3 receptor (CD123), necessary for DC survival. We also report down-regulation of cell surface CD86, a molecule required for T cell co-stimulation. T helper cell down-regulation of CD45RB is redolent of an anti-inflammatory phenotype with poor proliferative capacity. The definitive causes of our findings and the consequences and role that these findings play in the pathogenesis of MPS are unclear, but may be in response to lysosomal storage of unmetabolized HS and DS.

The human cathelicidin, LL-37, induces granzyme-mediated apoptosis in cytotoxic T lymphocytes

LL-37 is a human cationic host defense peptide (antimicrobial peptide) belonging to the cathelicidin family of peptides. In this study, LL-37 was shown to kill stimulated CD8(+) T cells (Cytotoxic T lymphocytes; CTLs) via apoptosis, while having no cytotoxic effect on non-stimulated CD8(+) or CD4(+) T cells or stimulated CD4(+) T cells. Of interest, the CD8(+) cells were much more sensitive to LL-37 than many other cell types. LL-37 exposure resulted in DNA fragmentation, chromatin condensation, and the release of both granzyme A and granzyme B from intracellular granules. The importance of granzyme family members in the apoptosis of CTLs following LL-37 treatment was analyzed by using C57BL/6 lymphocytes obtained from mice that were homozygous for null mutations in the granzyme B gene, the granzyme A gene, or both granzymes A and B. Granzymes A and B were both shown to play an important role in LL-37-induced apoptosis of CTLs. Further analysis revealed that apoptosis occurred primarily through granzyme A-mediated caspase-independent apoptosis. However, caspase-dependent cell death was also observed. This suggests that LL-37 induces apoptosis in CTLs via multiple different mechanisms, initiated by the LL-37-induced leakage of granzymes from cytolytic granules. Our results imply the existence of a novel mechanism of crosstalk between the inflammatory and adaptive immune systems. Cells such as neutrophils, at the site of a tumor for example, could influence the effector, activity of CTL through the secretion of LL-37.

Blistering skin diseases: a bridge between dermatopathology and molecular biology

Although dermatopathology and molecular biology are often considered to be separate laboratory disciplines, the respective approaches are far from mutually exclusive. This is certainly the case for understanding the pathology of blistering skin diseases, both acquired and inherited. For example, in toxic epidermal necrolysis, dermatopathology in isolation may provide few clues to disease pathogenesis. There is widespread keratinocyte apoptosis and a variable infiltrate of cytotoxic T cells, but morphology alone offers little insight into what causes the epidermal destruction. In contrast, molecular biology studies have revealed several key processes that help explain the keratinocyte death, including increased expression of death receptors and their ligands on keratinocyte cell membranes as well as the presence of local or systemic immunocyte-derived cytolytic granules. For some inherited blistering diseases, however, such as epidermolysis bullosa, the molecular pathology is complex and difficult to unravel in isolation, yet the addition of dermatopathology is helpful in focusing molecular investigations. Notably, immunolabelling of cell adhesion proteins using specific antibody probes can identify reduced or absent immunoreactivity for candidate genes/proteins. Bridging dermatopathology and molecular biology investigations facilitates a greater understanding of disease processes, improves diagnostic accuracy, and provides a basis for the development and appraisal of new treatments.

Divergent effects of norepinephrine, dopamine and substance P on the activation, differentiation and effector functions of human cytotoxic T lymphocytes

Background

Neurotransmitters are important regulators of the immune system, with very distinct and varying effects on different leukocyte subsets. So far little is known about the impact of signals mediated by neurotransmitters on the function of CD8⁺ T lymphocytes. Therefore, we investigated the influence of norepinephrine, dopamine and substance P on the key tasks of CD8⁺ T lymphocytes: activation, migration, extravasation and cytotoxicity.

Results

The activation of naïve CD8⁺ T lymphocytes by CD3/CD28 cross-linking was inhibited by norepinephrine and dopamine, which was caused by a downregulation of interleukin (IL)-2 expression via Erk1/2 and NF-κB inhibition. Furthermore, all of the investigated neurotransmitters increased the spontaneous migratory activity of naïve CD8⁺ T lymphocytes with dopamine being the strongest inducer. In contrast, activated CD8⁺ T lymphocytes showed a reduced migratory activity in the presence of norepinephrine and substance P. With regard to extravasation we found norepinephrine to induce adhesion of activated CD8⁺ T cells: norepinephrine increased the interleukin-8 release from endothelium, which in turn had effect on the activated CXCR1⁺ CD8⁺ T cells. At last, release of cytotoxic granules from activated cells in response to CD3 cross-linking was not influenced by any of the investigated neurotransmitters, as we have analyzed by measuring the β-hexosamidase release.

Conclusion

Neurotransmitters are specific modulators of CD8⁺ T lymphocytes not by inducing any new functions, but by fine-tuning their key tasks. The effect can be either stimulatory or suppressive depending on the activation status of the cells.

Calcium influx and signaling in cytotoxic T-lymphocyte lytic granule exocytosis

Cytotoxic T lymphocytes (CTLs) kill targets by releasing cytotoxic agents from lytic granules. Killing is a multi-step process. The CTL adheres to a target, allowing its T-cell receptors to recognize antigen. This triggers a signal transduction cascade that leads to the polarization of the microtubule cytoskeleton and granules towards the target, followed by exocytosis that occurs specifically at the site of contact. As with cytokine production by helper T cells (Th cells), target cell killing is absolutely dependent on Ca2+ influx, which is involved in regulating both reorientation and release. Current evidence suggests that Ca2+ influx in CTLs, as in Th cells, occurs via depletion-activated channels. The molecules that couple increases in Ca2+ to reorientation are unknown. The Ca2+/calmodulin-dependent phosphatase calcineurin, which plays a critical role in cytokine production by Th cells, is also involved in lytic granule exocytosis, although the relevant substrates remain to be identified and calcineurin activation is only one Ca2+-dependent step involved. There are thus striking similarities and important differences between Ca2+ signals in Th cells and CTLs, illustrating how cells can use similar signal transduction pathways to generate different functional outcomes.

Zinc transporter ZIP8 (SLC39A8) and zinc influence IFN-gamma expression in activated human T cells

The zinc transporter ZIP8 is highly expressed in T cells derived from human subjects. T cell ZIP8 expression was markedly up-regulated upon in vitro activation. T cells collected from human subjects who had received oral zinc supplementation (15 mg/day) had higher expression of the activation marker IFN-gamma upon in vitro activation, indicating a potentiating effect of zinc on T cell activation. Similarly, in vitro zinc treatment of T cells along with activation resulted in increased IFN-gamma expression with a maximum effect at 3.1 microM. Knockdown of ZIP8 in T cells by siRNA decreased ZIP8 levels in nonactivated and activated cells and concomitantly reduced secretion of IFN-gamma and perforin, both signatures of activation. Overexpression of ZIP8 by transient transfection caused T cells to exhibit enhanced activation. Confocal microscopy established that ZIP8 is localized to the lysosome where ZIP8 abundance is increased upon activation. Loss of lysosomal labile zinc in response to activation was measured by flow cytometry using a zinc fluorophore. Zinc between 0.8 and 3.1 microM reduced CN phosphatase activity. CN was also inhibited by the CN inhibitor FK506 and ZIP8 overexpression. The results suggest that zinc at low concentrations, through inhibition of CN, sustains phosphorylation of the transcription factor CREB, yielding greater IFN-gamma expression in T cells. ZIP8, through control of zinc transport from the lysosome, may provide a secondary level of IFN-gamma regulation in T cells.

Protein kinase Cdelta regulates antigen receptor-induced lytic granule polarization in mouse CD8+ CTL

Lytic granule exocytosis is the major pathway used by CD8+ CTL to kill virally infected and tumor cells. Despite the obvious importance of this pathway in adaptive T cell immunity, the molecular identity of enzymes involved in the regulation of this process is poorly characterized. One signal known to be critical for the regulation of granule exocytosis-mediated cytotoxicity in CD8+ T cells is Ag receptor-induced activation of protein kinase C (PKC). However, it is not known which step of the process is regulated by PKC. In addition, it has not been determined to date which of the PKC family members is required for the regulation of lytic granule exocytosis. By combination of pharmacological inhibitors and use of mice with targeted gene deletions, we show that PKCdelta is required for granule exocytosis-mediated lytic function in mouse CD8+ T cells. Our studies demonstrate that PKCdelta is required for lytic granule exocytosis, but is dispensable for activation, cytokine production, and expression of cytolytic molecules in response to TCR stimulation. Importantly, defective lytic function in PKCdelta-deficient cytotoxic lymphocytes is reversed by ectopic expression of PKCdelta. Finally, we show that PKCdelta is not involved in target cell-induced reorientation of the microtubule-organizing center, but is required for the subsequent exocytosis step, i.e., lytic granule polarization. Thus, our studies identify PKCdelta as a novel and selective regulator of Ag receptor-induced lytic granule polarization in mouse CD8+ T cells.