Risk of chronic pancreatitis in carriers of the c.180C>T (p.Gly60=) CTRC variant: case-control studies and meta-analysis

Chymotrypsin C (CTRC) is a digestive serine protease produced by the pancreas that regulates intrapancreatic trypsin activity and provides a defensive mechanism against chronic pancreatitis (CP). CTRC exerts its protective effect by promoting degradation of trypsinogen, the precursor to trypsin. Loss-of-function missense and microdeletion variants of CTRC are found in around 4% of CP cases and increase disease risk by approximately 3-7-fold. In addition, a commonly occurring synonymous CTRC variant c.180C>T (p.Gly60=) was reported to increase CP risk in various cohorts but a global analysis of its impact has been lacking. Here, we analyzed the frequency and effect size of variant c.180C>T in Hungarian and pan-European cohorts, and performed meta-analysis of the new and published genetic association data. When allele frequency was considered, meta-analysis revealed an overall frequency of 14.2% in patients and 8.7% in controls (allelic odds ratio (OR) 2.18, 95% confidence interval (CI) 1.72-2.75). When genotypes were examined, c.180TT homozygosity was observed in 3.9% of CP patients and in 1.2% of controls, and c.180CT heterozygosity was present in 22.9% of CP patients and in 15.5% of controls. Relative to the c.180CC genotype, the genotypic OR values were 5.29 (95% CI 2.63-10.64), and 1.94 (95% CI 1.57-2.38), respectively, indicating stronger CP risk in homozygous carriers. Finally, we obtained preliminary evidence that the variant is associated with reduced CTRC mRNA levels in the pancreas. Taken together, the results indicate that CTRC variant c.180C>T is a clinically relevant risk factor, and should be considered when genetic etiology of CP is investigated.

Faster recovery and bowel movement after early oral feeding compared to late oral feeding after upper GI tumor resections: a meta-analysis

Background

There were more than 1 million new cases of stomach cancer concerning oesophageal cancer, there were more than 600,000 new cases of oesophageal cancer in 2020. After a successful resection in these cases, the role of early oral feeding (EOF) was questionable, due to the possibility of fatal anastomosis leakage. It is still debated whether EOF is more advantageous compared to late oral feeding. Our study aimed to compare the effect of early postoperative oral feeding and late oral feeding after upper gastrointestinal resections due to malignancy.

Methods

Two authors performed an extensive search and selection of articles independently to identify randomized control trials (RCT) of the question of interest. Statistical analyses were performed including mean difference, odds ratio with 95% confidence intervals, statistical heterogeneity, and statistical publication bias, to identify potential significant differences. The Risk of Bias and the quality of evidence were estimated.

Results

We identified 6 relevant RCTs, which included 703 patients. The appearance of the first gas (MD = -1.16; p = 0.009), first defecation (MD = -0.91; p < 0.001), and the length of hospitalization (MD = -1.92; p = 0.008) favored the EOF group. Numerous binary outcomes were defined, but significant difference was not verified in the case of anastomosis insufficiency (p = 0.98), pneumonia (p = 0.88), wound infection (p = 0.48), bleeding (p = 0.52), rehospitalization (p = 0.23), rehospitalization to the intensive care unit (ICU) (p = 0.46), gastrointestinal paresis (p = 0.66), ascites (p = 0.45).

Conclusion

Early postoperative oral feeding, compared to late oral feeding has no risk of several possible postoperative morbidities after upper GI surgeries, but has several advantageous effects on a patient's recovery.

Systematic Review Registration

identifier, CRD 42022302594.

Common calcium-sensing receptor (CASR) gene variants do not modify risk for chronic pancreatitis in a Hungarian cohort

The calcium-sensing receptor (CASR) is expressed in the pancreas where it might regulate calcium concentrations in pancreatic secretions. Two independent studies reported conflicting results claiming that commonly occurring missense variants of the CASR gene are risk factors for chronic pancreatitis (CP). Here, we attempted to replicate the association between CASR variants and CP. We analyzed 337 patients and 840 controls from the Hungarian National Pancreas Registry either by direct sequencing of exon 7 and the flanking noncoding regions or by TaqMan SNP genotyping assays. We identified two common missense variants, c.2956G>T (p.A986S), and c.2968A>G (p.R990G), three low-frequency variants, c.3031C>G (p.Q1011E), c.2610G>A (p.E870=) and c.∗60T>A, and 8 rare variants including the novel variant c.1895G>A (p.G632D). When allelic or genotype distributions were considered, none of the CASR variants associated with CP. Subgroup analysis of nonalcoholic versus alcoholic patients revealed no disease association either. Our results demonstrate that common CASR variants do not modify the risk for CP and should not be considered as genetic risk factors in the clinical setting.

Electrophysiologic perturbations and arrhythmogenic activity caused by activation of the Fas receptor in murine ventricular myocytes: role of the inositol trisphosphate pathway

INTRODUCTION

Experimental evidence suggests a major role for Fas receptor activation in a wide range of myocardial pathologies. Because clinical situations, which are likely to be associated with Fas activation, are accompanied by a variety of ventricular arrhythmias, the major goal of this study was to investigate the ionic mechanisms responsible for these phenomena.

METHODS AND RESULTS

To delineate the origin of Fas-mediated electrophysiologic perturbations, the transient outward K+ current I(to) and the L-type Ca2+ current I(Ca,L) were studied in murine ventricular myocytes treated with the Fas-activating monoclonal antibody Jo2. Jo2 decreased I(to) (4.36 +/- 1.2 pA/pF vs 17.48 +/- 2.36 pA/pF in control, V(M) = +50 mV; P < 0.001) and increased I(Ca,L) (-13.17 +/- 1.38 pA/pF vs -3.94 +/- 0.78 pA/pF in control, V(M) = 0 mV; P < 0.001). Pretreatment of ventricular myocytes with ryanodine or thapsigargin prevented the electrophysiologic effects of Jo2, suggesting that [Ca2+]i elevation is important for Fas-mediated action. In agreement with our previous studies demonstrating dependence of Fas-based myocyte dysfunction on an intact inositol trisphosphate (1,4,5-IP3) pathway, the effects of Jo2 on I(to) and I(Ca,L) were prevented by the phospholipase C (generates 1,4,5-IP3) blocker U73122, and by xestospongin C (tested with I(to)), a specific blocker of IP3-operated sarcoplasmic reticulum Ca2+ release channels. Furthermore, intracellular perfusion with 1,4,5-IP3, but not with 1,3,4-IP3, caused electrophysiologic effects resembling those of Jo2.

CONCLUSION

Decreased I(to) and increased I(Ca,L) underlie Fas-induced action potential alterations and arrhythmias in murine ventricular myocytes, effects that appear to be mediated by 1,4,5-IP3-induced intracellular calcium release.

Vocal cord augmentation with cultured autologous fibroblasts

Bovine collagen is an acceptable agent for vocal cord medialization; however, it produces only a temporary effect. As a foreign protein bovine collagen is susceptible to host collagenase and can induce immune response. Autologous collagen has become recently available, but it is less effective as a medialization agent. The study examines human skin fibroblasts growing in culture. Human skin bioptates were taken from the retroauricular area. Fibroblasts in culture were tested for scar contractility and ability to produce type I collagen (by flow cytometry with labeled antibodies). After five passages in culture the cells produced normal type I collagen, exhibited normal contractility, and did not induce no tumors in nude mice.

Tumor immunity in perforin-deficient mice: a role for CD95 (Fas/APO-1)

CTL and NK cells use two distinct cytocidal pathways: 1) perforin and granzyme based and 2) CD95L/CD95 mediated. The former requires perforin expression by the effectors (CTL or NK), whereas the latter requires CD95 (Fas/APO-1) expression by the target. We have investigated how these two factors contribute to tumor immune surveillance by studying the immunity of perforin-deficient mice against the progressor C57BL/6 Lewis lung carcinoma 3LL, which expresses no CD95 when cultured in vitro. Unexpectedly, the results indicated that the perforin-independent CD95L/CD95 pathway of CTL/NK plays a role in acting against D122 and Kb39.5 (39.5) high and low metastatic sublines, respectively, derived from the 3LL tumor. Although no membrane-bound CD95 was detected on cultured D122 and 39. 5 cells, surface CD95 expression on both D122 and 39.5 was considerably up-regulated when the tumors were grown in vivo. A similarly enhanced expression of CD95 was observed with three additional tumors; LF-, BW, and P815, injected into syngeneic and allogeneic mice. The finding of up-regulated CD95 expression on tumor cells placed in vivo suggests that a CD95-based mechanism plays a role in tumor immunity at early stages of tumor growth. Consequently, the progressive down-regulation of CD95 expression during tumor progression may indeed be an escape mechanism as previously reported. Together, these results suggest a role for CD95-dependent, perforin-independent immunity against certain tumors.

Cardiac dysfunction in murine autoimmune myocarditis

We have investigated the pathophysiological basis of cardiac dysfunction in autoimmune myocarditis and in the resulting dilated cardiomyopathy. To this end we utilized the myosin-induced autoimmune myocarditis model in BALB/c mice. Myocarditis has been found to be associated with massive ventricular lymphocyte infiltration and a 50% reduction in tail artery blood flow, reflecting the depressed cardiac function in myocarditis. Action potential characteristics of control and diseased isolated ventricular myocytes were (mean+/-SEM): resting potential: -68.1+/-1. 1,-68.3+/-0.7 mV; action potential amplitude: 96.5+/-10.4, 92.3+/-4. 4 mV; action potential duration at 80% repolarization (APD80) 38+/-5, 116+/-24* ms; * P<0.05. We utilized the whole cell voltage clamp technique to explore ion currents involved in APD prolongation and arrhythmogenic activity, and found that in diseased myocytes the transient outward current (Ito) was markedly attenuated. At a membrane potential of +40 mV, in control and in diseased myocytes, I(to) current density was 14.7+/-1.5 and 6.5+/-1.4 pA/pF, respectively, P<0.005. In contrast, the L-type Ca2+current (ICa,L) remained unchanged. To further explore the basis for cardiac impairment, we simultaneously measured [Ca2+]i transient and contraction in isolated normal and diseased myocytes. The major findings indicated that both the relaxation kinetics of [Ca2+]i transients and myocyte contraction were significantly faster in the diseased myocytes. In conclusion, substantial, potentially reversible, electrophysiological and mechanical perturbations in ventricular myocytes from mice with myosin-induced autoimmune myocarditis appear to contribute to disease-related cardiac dysfunction.

The regulation of CD95 ligand expression and function in CTL

Previous studies with CTL lines and CTL hybridomas have suggested that functional CD95 (APO-1/Fas)-ligand (CD95L) expression on effector CTLs is a consequence of specific CTL-target recognition and TCR triggering of newly transcribed CD95L. Such a control on the expression of CD95L could provide a double safeguard for killing only cognate target cells. Here the regulation of CD95L expression and function was tested in in vivo primed, alloreactive peritoneal exudate CTL (PEL) from perforin-deficient (P0) mice. CD95L-based, PEL-mediated cytotoxicity was blocked by brefeldin A, an inhibitor of intracellular protein transport, but not by the protein synthesis inhibitor emetine, the immunosuppressive drug cyclosporin A, or the DNA transcription inhibitor actinomycin D. CD95L mRNA transcripts in freshly isolated PEL were shown by RT-PCR; CD95L surface expression was evident by staining with Fas-Fc as well as CD95L Abs. Undiminished CD95L expression and cytocidal activity were found in PEL incubated for 48 h in culture, without adding Ag, mitogen, or cytokines. PEL expressed functional CD95L, yet exhibited target cell-specific killing, except when encountering high CD95-expressing cells. The results indicate that PEL use CD95L probably expressed in the Golgi and/or on the cell surface and do not require newly transcribed CD95L upon target cell conjugation. Hence the TCR-triggered recruitment of preformed CD95L, rather than its biosynthesis, controls CD95L-based specific lysis induced by CTL.

Fas (CD95/Apo-1)-mediated damage to ventricular myocytes induced by cytotoxic T lymphocytes from perforin-deficient mice: a major role for inositol 1,4,5-trisphosphate

Cytotoxic T lymphocytes (CTLs) that infiltrate the heart are important immune effectors implicated in heart transplant rejection, myocarditis, and other cardiomyopathies. To investigate the mechanism(s) underlying CTL damage to the myocardium through activation of the Fas receptor (Fas/CD95/Apo-1) by the Fas ligand, we explored the interaction between peritoneal exudate CTLs (PELs), derived from perforin gene-knockout (P-/-) mice, and murine ventricular myocytes. Fas expression on isolated ventricular myocytes was demonstrated immunohistochemically. Action potentials, [Ca2+]i transients, and contractions of myocytes conjugated to P-/- PELs or treated with the apoptosis-inducing anti-Fas monoclonal antibody Jo2 were recorded. Action potential characteristics of nonconjugated myocytes and myocytes conjugated with P-/- PELs were, respectively, as follows: Vm, -73.2+/-1.5 and -53.6+/-6.4 mV (mean+/-SEM); action potential amplitude, 117.9+/-3.9 and 74.3+/-21.2 mV; and action potential duration at 80% repolarization, 17+/-6 and 42+/-13 milliseconds (all P<.05). P-/- PELs also induced early and delayed afterdepolarizations as well as arrhythmogenic activity. Diastolic [Ca2+]i increased during the cytocidal interaction with P-/- PELs, from a fluorescence ratio of 0.82+/-0.05 (n=7) to 1.98+/-0.09 (n=13) (P<.05). All of the effects caused by P-/- PELs were reproduced by incubating the myocytes with Jo2. Heparin (50 microg/mL), an antagonist of inositol trisphosphate (IP3)-operated sarcoplasmic reticulum Ca2+ channels, or U-73122 (2 micromol/L), a phospholipase C inhibitor, but not the inactive agonist U-73343, prevented Fas-mediated myocyte dysfunction. Additionally, intracellular application (through the patch pipette) of the active IP3 analogue, inositol 1,4,5-trisphosphate, but not the inactive analogue, inositol 1,3,4-trisphosphate, caused electrophysiological changes resembling those resulting from P-/- PELs and Jo2, suggesting that CTL-induced Fas-based myocyte dysfunction is mediated by IP3. We conclude that a Fas-based perforin-independent mechanism of CTL action can account for the immunopathology seen in the allotransplanted heart, myocarditis, and dilated cardiomyopathy.

Activation of influenza-specific memory cytotoxic T lymphocytes by Concanavalin A stimulation

Traditionally, the in vitro activation of virus-specific memory cytotoxic T lymphocytes (CTLs) has been achieved by stimulating the CTLs with antigen-presenting cells (APCs) infected with an appropriate virus or pulsed with virus-specific antigenic peptides. Here, we describe the utilization of the polyclonal activator Concanavalin A (ConA) for in vitro restimulation of memory CTLs from virus-primed mice. Using this simple method, the activation of splenocytes with ConA for 3 days (i) eliminates the need to stimulate with virus-pulsed APCs and (ii) generates CD8+ CTLs that exhibit virus specificity and MHC-restricted lytic activity similar to CTLs obtained by conventional viral restimulation. In vitro ConA stimulation of splenocytes from BALB/c mice primed with the A/Texas/77 or A/Japanese/57 strain of influenza virus and from C57L/J mice infected with the A/Texas strain, generated CTLs with specific lytic activity. Hence reactivation of memory CTLs by this method is a general phenomenon rather than a mouse or viral strain-specific one. The ConA stimulation method used here had a recall of long-term (1 year) memory CTLs that effectively lysed virally infected targets. Further ConA-stimulated effector lymphocytes from virally primed animals have been shown to recognize and subsequently lyse target cells pulsed with virus or virus-derived peptides. The ConA reactivation of specific anti-viral CTLs may facilitate (i) studying anti-viral CTL responses and (ii) identifying of viral epitopes when unknown or when appropriate viral stimulation is impossible.

Channel formation and [Ca2+]i accumulation induced by perforin N-terminus peptides: comparison with purified perforin and whole lytic granules

Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells express the pore forming protein perforin, which contributes to lymphocytotoxicity. The hallmark of perforin action is opening high-conductance transmembrane channels that enable massive influx of Ca2+ ions (deleterious to many cell types), as well as granzymes, which may trigger the apoptotic pathway. To explore the functional domains in the perforin molecule, we investigated in PN71 lymphocytes, the ability of perforin N-terminus synthetic peptides (compared to purified perforin and perforin-containing lytic granules), to cause intracellular Ca2+ ([Ca2+]i) accumulation and open transmembrane channels. To this end, we used the whole cell recording technique and Indo 1 fluorescence to measure membrane currents and [Ca2+]i, respectively. We have demonstrated that the N-terminus peptide Hu-34 (amino acids 1-34) closely resembled perforin action, reflected by [Ca2+]i accumulation and channel activity, while shorter peptides (e.g., Hu-16) generated mostly short-lived channels but no [Ca2+]i elevation. Hence, the first 34 amino acids of the perforin N-terminus sequence are sufficient for the perforin action.

Involvement of the IP3 cascade in the damage to guinea-pig ventricular myocytes induced by cytotoxic T lymphocytes

We have shown previously that the interaction between cytotoxic T lymphocytes (CTL) and ventricular myocytes, an in vitro model for heart transplant rejection, results in electrophysiological and morphological alterations indicative of overload of the intracellular [Ca2+] ([Ca2+]i). Since these deleterious effects cannot be accounted for by increased L-type Ca2+ current (ICa,L), we hypothesize that [Ca2+]i overload due to Ca2+ release from intracellular stores, e.g. sarcoplasmic reticulum (SR), is initiated by CTL-induced activation of the inositol trisphosphate (IP3) cascade. Patch-clamp and fura-2-fluorescence techniques were utilized to record transmembrane potentials and [Ca2+]i from ventricular myocytes bound to peritoneal exudate CTL (PEL). In ventricular myocyte-PEL conjugates (after 60 min), resting potential was reduced (compared with the nonconjugated state) from -80.9 +/- 0.7 to -59.9 +/- 2.5 mV, action potential amplitude from 139.5 +/- 1.4 to 80.6 +/- 1.7 mV and action potential duration to 50% repolarization (APD50) from 797 +/- 97 to 52 +/- 12 ms. The ratio of fluorescence at 340 and 380 nm (R340/380) increased from a control value (in nonconjugated myocytes) of 0.71 +/- 0.02 to 2.07 +/- 0.03, 30 min, after conjugate formation, and exceeded 4.0 at 60 min, before myocyte destruction. Heparin (50 micrograms/ml), an antagonist of IP3-induced Ca2+ release from SR channels, or U-73122 (2 microM), a phospholipase C (PLC) inhibitor (drugs were included in the pipette solution), prevented PEL-induced morphological and electrophysiological alterations. Accordingly, heparin attenuated the PEL-induced increase in [Ca2+]i; after 60 min of PEL-myocyte interaction, R340/380 was 1.15 +/- 0.09 (compared with approximately 4.0 in the absence of heparin). The results indicate that CTL-mediated damage to ventricular myocytes is, at least partially, mediated by PLC activation and IP3-induced Ca2+ release from intracellular stores. Pharmacological targeting of IP3 in heart transplant rejection is thus suggested.

Fluorescence depolarization as an early measure of T lymphocyte stimulation

We have used the Cellscan, an apparatus capable of measuring optical properties of individual cells, to study changes in fluorescence polarization associated with T cell stimulation. We show that the fluorescence polarization of human peripheral blood lymphocytes (PBL) labeled with fluorescein diacetate (FDA) is markedly reduced upon exposure to the mitogenic lectins phytohemagglutinin (PHA), concanavalin A (ConA), or to phorbol esters. Methyl alpha-D-mannopyranoside (alphaMM) is able to reverse the depolarizing effect induced by ConA as long as the cells are not committed to proliferate. H7 and staurosporin, both inhibitors of protein kinase C (PKC), inhibit the depolarization induced by PHA. The mitogen-induced depolarization is dependent on metabolic energy. The results support the use of fluorescence depolarization of FDA-labeled PBL, monitored by the Cellscan, as a sensitive means of measuring early lymphocyte stimulation.

Killing mechanisms of cytotoxic lymphocytes

Killer lymphocytes are primary immune effectors of virus, certain bacteria, and tumor immunity and play a role in autoimmunity and transplant rejection. This article reviews progress in deciphering the mechanisms by which they kill target cells through induction of apoptosis by either the secretory, perforin/granzyme-based pathway or the nonsecretory pathway, (i.e., by triggering the cell-surface death receptor Fas (CD95) by the membrane-bound Fas ligand of the killer).

Abnormal glutathione and sulfate levels after interleukin 6 treatment and in tumor-induced cachexia

Excessive urea excretion associated with a negative nitrogen balance and massive loss of skeletal muscle mass (cachexia) is a frequent life threatening complication in malignancies and HIV infection. As these patients have often elevated interleukin-6 (IL-6) and abnormally low cystine levels, we have now determined the intracellular levels of glutathione and other cysteine derivatives in the liver and muscle tissue of IL-6-treated or tumor-bearing C57BL/6 mice. IL-6 treatment or inoculation of the MCA-105 fibrosarcoma caused a significant increase in hepatic gamma-glutamyl-cysteine synthetase activity and a decrease in the sulfate level, glutamine/urea ratio, and glutamine/glutamate ratio, suggesting that a decrease of the proton generating cysteine catabolism in the liver may increase carbamoyl-phosphate synthesis and urea formation at the expense of net glutamine synthesis. Treatment with cysteine, conversely, caused an increase in sulfate, glutamine/urea ratios, and glutamine/glutamate ratios and may thus be a useful therapeutic tool in clinical medicine. In contrast to the liver, muscle tissue of tumor-bearing mice showed decreased glutathione and increased sulfate levels, suggesting that the cysteine pool may be drained by an increased cysteine catabolism in this tissue. The findings indicate that tumor cachexia is triggered initially by IL-6 and is later sustained by processes driven by an abnormal cysteine metabolism in different organs.-Hack, V., Gross, A., Kinscherf, R., Bockstette, M., Fiers, W., Berke, G., and Dröge, W. Abnormal glutathione and sulfate levels after interleukin 6 treatment and in tumor-induced cachexia.

Cell-mediated cytotoxicity results from, but may not be critical for, primary allograft rejection

Tumor cells insensitive to lysis through the Fas and TNF pathways were injected either subcutaneously or into the peritoneal cavities of allogeneic perforin-less (P0) and perforin wild-type (P2) mice. In three of four cases, the tumors were rejected equally rapidly in both strains of mice. Rejection was accompanied by vigorous in vitro cytotoxicity in P2, but not in P0 mice. The rapid clearance of allografted cells in mice where all three known cytolytic pathways are seriously compromised raises important questions about the involvement of cell-mediated cytotoxicity, as defined by current assay techniques, in primary allograft rejection.

Cell-mediated cytotoxicity results from, but may not be critical for, primary allograft rejection

Tumor cells insensitive to lysis through the Fas and TNF pathways were injected either subcutaneously or into the peritoneal cavities of allogeneic perforin-less (P0) and perforin wild-type (P2) mice. In three of four cases, the tumors were rejected equally rapidly in both strains of mice. Rejection was accompanied by vigorous in vitro cytotoxicity in P2, but not in P0 mice. The rapid clearance of allografted cells in mice where all three known cytolytic pathways are seriously compromised raises important questions about the involvement of cell-mediated cytotoxicity, as defined by current assay techniques, in primary allograft rejection.

Interaction of cytotoxic T lymphocytes and guinea pig ventricular myocytes. Pharmacological modulation by blocking K+ currents in cytotoxic T lymphocytes

Infiltrating cytotoxic T lymphocytes (CTLs) are important immune effectors that damage the myocardium during heart transplant rejection as well as in cardiomyopathy and Chagas' heart disease. We have previously shown that in an in vitro model of murine-derived peritoneal exudate CTL (PEL)-guinea pig ventricular myocyte interaction, PEL induced in conjugated myocytes reduction of resting membrane potential and action potential (AP) amplitude, shortening of AP duration, delayed afterdepolarizations (DADs), and myocyte contracture and destruction. Since these findings indicated that cytotoxicity was largely caused by [Ca2+]i overload, in the present study we tested the hypothesis that blocking the L-type Ca2+ current (ICa,L) in the myocyte will eliminate the trigger for Ca2+ release from intracellular stores and will reduce [Ca2+]i overload and subsequent myocyte deterioration. CoCl2 (3 mmol/L) prevented PEL-induced AP changes, induction of DADs, and myocyte destruction. Since verapamil (2 mumol/L) was ineffective, indicating that the CoCl2 protection was not due to block of ICa,L, we tested whether the different action of these Ca2+ channel blockers was due to their differential effect on the PEL's K+ current (IK), previously shown to participate in lymphocyte activation and cytotoxicity. In agreement with their protective efficacy, CoCl2 but not verapamil blocked IK in PELs, suggesting that this is the mechanism for the protection provided by CoCl2. To support this notion, we tested the effect of the scorpion-derived peptide margatoxin (10 nmol/L), a specific K+ channel blocker in lymphocytes, on PEL-myocyte interaction and on PEL's IK; margatoxin prevented PEL-induced cytotoxicity and also blocked IK in PEL. Based on these findings, an alternative modality for attenuating CTL-induced lymphocytotoxicity is proposed.

Regression of established murine carcinoma metastases following vaccination with tumour-associated antigen peptides

The cure of micrometastases following surgery is the major goal of cancer immunotherapy. We have recently isolated tumour-associated antigen (TAA) peptides, MUT 1 and MUT 2, derived from a mutated connexin 37 gap-junction protein, from the malignant 3LL-D122 murine lung carcinoma. We now report that synthetic MUT 1 or MUT 2 induces effective antitumour cytoxic T lymphocytes. Peptide vaccines protect mice from spontaneous metastases of 3LL-D122 tumours. Moreover, peptide vaccines reduce metastatic loads in mice carrying pre-established micrometastases. Tumour-specific immunity was primarily mediated by CD8+ T cells. This is the first evidence that peptide therapy may be effective in treatment of residual tumours and provides a rationale for the development of peptide vaccines as a modality for cancer therapy.

PELs and the perforin and granzyme independent mechanism of CTL-mediated lysis

The central role of CTLs in immunopathology accounts for the increasing interest in deciphering the mechanism whereby they kill at the molecular level. Recent studies show that CTLs have two molecularly distinct lytic mechanisms at their disposal. The first involves the direct effect(s) of the pore-forming protein perforin, possibly in conjunction with granzymes. In recent years, experiments conducted in our laboratory led to an alternative pathway, of receptor-mediated mechanism for CTL killing, involving neither the secretion nor the lytic action of the pore-forming protein perforin or of granzymes. By this mechanism, engagement of a CTL membrane ligand and an apoptosis-inducing target cell surface receptor triggers the disintegration of the CTL-bound target cell. Cross-linking of apoptosis-inducing target cell surface molecules (e.g. Fas), induced upon binding of CTL ligands (e.g. Fas-L), may be required and sufficient to trigger target cell apoptosis. Intracellular lethal signals emanating from the cross-linked intracellular death domain of Fas are postulated.

Lytic reaction of in vivo primed peritoneal exudate CTL. Induction of high-conductance single channels in the target cell membrane

CTL, primary effectors in immune responses, deliver a "lethal hit" signal to target cells, causing their destruction. The precise membrane events associated with the lethal hit remain elusive. We investigated the signal(s) mediating destruction of tumor target cells (EL4) by perforin-deficient peritoneal exudate CTL (PEL). We utilized patch clamp techniques to record electrophysiological events associated with the cytolytic interaction of PEL and EL4 in isolated conjugates. PEL-EL4 interaction resulted in induction in EL4 cells, of single channels (followed by EL4 destruction), with a mean conductance of 437 pS and a reversal potential of -1.0 mV, suggestive of nonselective pathways. Similar channels were induced in EL4 cells conjugated with perforin-rich PEL blasts (PEB), by perforin, postnuclear extract from PEL (pnPEL) and from other cytotoxic lymphocytes, but not from noncytolytic lymphocytes. As similar channels were induced by pnPEL in EL4 membrane patches, we propose that these channels result from a direct effect of PEL-derived channel-forming substance(s) on the target cell's membrane. Importantly, postnuclear extracts from perforin-devoid cytotoxic PEL-hybridomas induced similar channels, suggesting the presence of a nonperforin, channel-forming activity in PEL and PEL-hybridomas. Based on the present study, we conclude that the delivery of the lethal hit by cytolytic PEL and PEL-hybridoma is associated with induction in the target cell of high-conductance channels, which most likely mediate its destruction. We propose that these channels are related to the Fas pathway of lymphocytotoxicity.

Lytic reaction of in vivo primed peritoneal exudate CTL. Induction of high-conductance single channels in the target cell membrane

CTL, primary effectors in immune responses, deliver a "lethal hit" signal to target cells, causing their destruction. The precise membrane events associated with the lethal hit remain elusive. We investigated the signal(s) mediating destruction of tumor target cells (EL4) by perforin-deficient peritoneal exudate CTL (PEL). We utilized patch clamp techniques to record electrophysiological events associated with the cytolytic interaction of PEL and EL4 in isolated conjugates. PEL-EL4 interaction resulted in induction in EL4 cells, of single channels (followed by EL4 destruction), with a mean conductance of 437 pS and a reversal potential of -1.0 mV, suggestive of nonselective pathways. Similar channels were induced in EL4 cells conjugated with perforin-rich PEL blasts (PEB), by perforin, postnuclear extract from PEL (pnPEL) and from other cytotoxic lymphocytes, but not from noncytolytic lymphocytes. As similar channels were induced by pnPEL in EL4 membrane patches, we propose that these channels result from a direct effect of PEL-derived channel-forming substance(s) on the target cell's membrane. Importantly, postnuclear extracts from perforin-devoid cytotoxic PEL-hybridomas induced similar channels, suggesting the presence of a nonperforin, channel-forming activity in PEL and PEL-hybridomas. Based on the present study, we conclude that the delivery of the lethal hit by cytolytic PEL and PEL-hybridoma is associated with induction in the target cell of high-conductance channels, which most likely mediate its destruction. We propose that these channels are related to the Fas pathway of lymphocytotoxicity.

The CTL's kiss of death

The potent and specific lytic activity of CTLs can occur by at least two distinct pathways. In the secretion and perforin-mediated pathway, the direct effect(s) on the target cell membrane of the pore-forming agent perforin, probably in conjunction with granzymes, also secreted from the CTLs, causes the target's demise. Intercytoplasmic transfer of granzymes is believed to be involved in inducing target apoptosis. In the Fas-mediated pathway, engagement of a CTL membrane ligand with an apoptosis-inducing target cell surface receptor, such as the FasL with Fas, triggers programmed disintegration of the CTL-bound target; secretion of granzymes and pore formation by perforin are not involved in this receptor-mediated mechanism. Despite the fundamental differences in their onset for both pathways, the downstream sequence of events that culminate in target cell apoptosis appears to be similar. Further studies will resolve this enigma.

The binding and lysis of target cells by cytotoxic lymphocytes: molecular and cellular aspects

The characteristics of cytotoxic T lymphocyte (CTL) and natural killer (NK) cell recognition of and binding to target cells (conjugate formation), and the precise mechanism(s) by which the target cells are triggered to undergo apoptotic cell lysis are now being deciphered at the cellular and molecular levels. Involvement of a multitude of cell surface molecules, in addition to T cell receptor (TCR)-major histocompatibility (MHC)-peptide complexes, in the binding and signalling for lymphocyte-mediated lysis has been demonstrated. Two proposed mechanisms of lymphotoxicity currently appear to be valid: (i) a membranolytic one initiated by the formation of pores in target cell membranes by secreted molecules of lymphocyte origin, such as perforin and granzymes, and (ii) a nonsecretory one initiated by receptor-mediated triggering of apoptosis-inducing target cell surface molecules, but not involving the secretion of pore-forming agents and granzymes. Perforin and granzymes are probably involved in lymphocyte activation and are likely mediators of the membranolytic pathway of lymphotoxicity. Existence of the nonsecretory and receptor-triggered lytic mechanism was indicated by (i) the prelytic fragmentation of the target cell's DNA, which precedes release of intracellular (51Cr-labeled) components, (ii) the demonstration of cytolytic effector cells that are either devoid of or express background levels of lytic granules and perforin, and (iii) the observation that some CTL lyse target cells under conditions at which perforin and granzymes are neither secreted nor lytic, e.g. [Ca2+]o < 1 micromolar. These two mechanisms are not mutually exclusive and are probably used by different types of effector cells or by the same effector cells at different stages of differentiation. In fact, recent perforin gene knock-out experiments support the existence of both.

Mechanisms whereby cytotoxic T lymphocytes damage guinea-pig ventricular myocytes in vitro

We studied possible mechanisms whereby cytotoxic T lymphocytes (CTL) damage the myocardium during the immunological rejection of the transplanted heart, by investigating the in vitro interaction between CTL and cardiac myocytes. We utilized the patch-clamp technique to record membrane currents and action potentials from concanavalin A-treated guinea-pig ventricular myocytes conjugated to mouse peritoneal exudate CTL (PEL). PEL-myocyte interaction reduced action potential duration at 50% repolarization (APD50) from 731.7 +/- 57.8 to 195.3 +/- 58.0 ms, action potential amplitude from 134.9 +/- 1.9 to 104.2 +/- 6.2 mV and resting membrane potential (Vm) from -80.9 +/- 0.5 to 72.5 +/- 1.5 mV. These changes were accompanied by generation of delayed afterdepolarizations, indicative of intracellular [Ca2+] overload. The electrophysiological alterations were associated with myocyte shortening (within 28.9 +/- 2.8 min) followed by complete cell destruction (within 43.5 +/- 4.3 min). To determine whether intracellular Ca2+ stores were involved in PEL-induced myocyte damage, the protective effects of ryanodine and caffeine were investigated. While ryanodine (10 microM) delayed the electrophysiological and morphological alterations, caffeine (5 mM) provided significant protection, suggesting that Ca2+ release from intracellular stores contributes to PEL-induced damage to the myocytes. Based on our findings, we suggest that the functional derangements seen in myocyte-lymphocyte conjugates can contribute to the overall decline in cardiac function during heart transplant rejection.

CTL induction by a tumour-associated antigen octapeptide derived from a murine lung carcinoma

Many mouse and human tumours express major histocompatibility complex (MHC) class I-associated antigens that constitute targets for syngeneic cytotoxic T lymphocytes (CTL). Genes encoding such antigens were isolated from a mouse mastocytoma and from human melanomas by genetic methods. Isolation and characterization of MHC class I-associated peptides has enabled specific anchor residues to be identified that are typical of peptides that bind to distinct class I molecules. Moreover, CTL specific to particular MHC-peptide combinations have been used to identify naturally occurring antigenic peptides in cell extracts and enabled them to be sequenced directly. Most known MHC ligands are of viral origin or are self peptides derived from normal proteins. Here we use total acid extraction and repeated fractionation to isolate and sequence Lewis lung carcinoma (3LL)-specific peptide(s), which shows sequence homology to the connexin 37 protein. Synthetic octamers based on these sequences bind to 'empty' H-2Kb molecules on RMA-S cells, sensitize RMA-S cells to lysis by specific anti-3LL CTL, and induce anti-tumour CTL. The tumour-associated peptide originates from mutated connexin 37 expressed in 3LL.

Effects of purified perforin and granzyme A from cytotoxic T lymphocytes on guinea pig ventricular myocytes

OBJECTIVE

Involvement of cytotoxic T lymphocytes (CTL) in heart transplant rejection as well as in viral myocarditis is well established, but the precise mechanisms whereby infiltrating CTL damage the myocardium are unknown. The aim of the study was to investigate how CTL derived perforin, the serine protease granzyme A, and the combination of both, damage guinea pig ventricular myocytes.

METHODS

Action potentials and membrane currents were recorded by means of the whole cell configuration from guinea pig ventricular myocytes.

RESULTS

Resembling the effects of CTL derived lytic granules, perforin caused gradual myocyte shortening and contracture, leading to complete loss of the rod shaped morphology and to cell destruction. These changes were preceded by shortening of action potential duration and reduction of resting potential and action potential amplitude, followed by complete inexcitability. Granzyme A alone was ineffective, but accelerated the deleterious effects of perforin on the morphological and electrophysiological properties of myocytes. The effects of perforin were further evaluated by measuring membrane currents by means of the whole cell voltage clamp. Perforin induced discrete changes in membrane current, reminiscent of single ion channels, with large conductance and open time of up to several seconds. Linear regression analysis of the channel I-V relations resulted in a conductance of 890 pS and a reversal potential of -7.6 mV. These results suggest that perforin induces large non-selective channels, which can account for most of the observed adverse effects.

CONCLUSIONS

As CTL participate in the immunological rejection of the transplanted heart, it is conceivable, but remains to be shown, that part of this damage is inflicted by perforin containing lytic granules.

The binding and lysis of target cells by cytotoxic lymphocytes: molecular and cellular aspects

The characteristics of cytotoxic T lymphocyte (CTL) and natural killer (NK) cell recognition of and binding to target cells (conjugate formation), and the precise mechanism(s) by which the target cells are triggered to undergo apoptotic cell lysis are now being deciphered at the cellular and molecular levels. Involvement of a multitude of cell surface molecules, in addition to T cell receptor (TCR)-major histocompatibility (MHC)-peptide complexes, in the binding and signalling for lymphocyte-mediated lysis has been demonstrated. Two proposed mechanisms of lymphotoxicity currently appear to be valid: (i) a membranolytic one initiated by the formation of pores in target cell membranes by secreted molecules of lymphocyte origin, such as perforin and granzymes, and (ii) a nonsecretory one initiated by receptor-mediated triggering of apoptosis-inducing target cell surface molecules, but not involving the secretion of pore-forming agents and granzymes. Perforin and granzymes are probably involved in lymphocyte activation and are likely mediators of the membranolytic pathway of lymphotoxicity. Existence of the nonsecretory and receptor-triggered lytic mechanism was indicated by (i) the prelytic fragmentation of the target cell's DNA, which precedes release of intracellular (51Cr-labeled) components, (ii) the demonstration of cytolytic effector cells that are either devoid of or express background levels of lytic granules and perforin, and (iii) the observation that some CTL lyse target cells under conditions at which perforin and granzymes are neither secreted nor lytic, e.g. [Ca2+]o < 1 micromolar. These two mechanisms are not mutually exclusive and are probably used by different types of effector cells or by the same effector cells at different stages of differentiation. In fact, recent perforin gene knock-out experiments support the existence of both.

Calcium channel blockers modify electrophysiological effects induced by lytic granules from cytotoxic T lymphocytes in guinea pig ventricular myocytes

Damage to myocytes by infiltrating cytotoxic lymphocytes, containing lytic granules and the pore-forming protein, perforin, thereof, probably contribute to the immunological rejection of the transplanted heart, to autoimmune diseases and possibly to congestive heart failure associated with myocarditis. In the present study we investigated whether electrophysiological and morphological changes induced in guinea pig ventricular myocytes by lytic granules extracted from cytotoxic T lymphocytes, are modified by L-type Ca++ channel blockers. The organic blockers, verapamil (2 microM) and nisoldipine (500 microM) were unable to prevent or inhibit any of the deleterious effects of lytic granule on action potential and myocyte morphology, and the granule-induced increase in the membrane current measured at the end of 300-msec clamp pulse. In contrast, the inorganic blockers CoCl2 (3 mM) and NiCl2 (4 mM) provided considerable protection against the granule actions mentioned above, but an equally potent Ca++ blocker, CdCl2 (3 mM) was ineffective. The protective efficacy of CoCl2 (and probably that of NiCl2) was most likely due to its capacity to reduce or block the generation by lytic granules/perforin of large-conductance (approximately 1400 pS) channels responsible for inducing Ca++ overload and cell destruction. We consider these studies of importance because they direct further studies aimed at developing effective means for attenuating cytotoxic T lymphocyte-induced tissue damage, for example during transplant rejection or in autoimmune diseases.

Mechanism of lymphocyte-mediated cytolysis: functional cytolytic T cells lacking perforin and granzymes

Involvement of the lytic protein perforin (c. 65,000 MW) and of granule proteases (granzymes) in cell lysis induced by cytolytic T lymphocytes (CTL) has been suggested, but is still controversial. For example, in vivo-primed peritoneal exudate CTL (PEL) have been found to express perforin and granzyme activity in amounts comparable to those found in non-lytic lymphocytes, although PEL are the most potent of all CTL. Exploiting several cloned CTL hybridomas developed in this laboratory and newly available molecular probes for detecting perforin, granzymes, protein and mRNA, we now directly demonstrate killer T lymphocytes which kill effectively and specifically, but are free from perforin, lytic granules and granzymes, all three of which have been postulated to be involved in lymphocyte-mediated killing. The CTL hybridomas are completely devoid of perforin and granzymes prior to, during, and after activation by antigen, mitogen or interleukin-2 (IL-2). The induction of lytic granules, perforin, and granzymes in the in vivo-primed PEL, but not in the cloned CTL hybridomas, upon cultivation in IL-2, further suggests the involvement of these constituents in antigen/lymphokine-induced CTL activation and differentiation rather than directly in their cytocidal activity. Together, these findings support a perforin- and granzyme-independent CTL lytic mechanism.

Mechanisms whereby lytic granules from cytotoxic T lymphocytes damage guinea pig ventricular myocytes

During immunological rejection of the transplanted heart, cytotoxic T lymphocytes (CTL) infiltrate the myocardium and by damaging the myocytes contribute to loss of function. To address one important aspect of heart transplant rejection, we investigated in guinea pig ventricular myocytes how CTL-derived lytic granules containing the pore-forming protein perforin reduce the membrane potential (VM) and cause cell damage. The reduction in VM was biphasic; within 8.4 +/- 1.9 min VM was reduced from a control value of -78.4 +/- 1.9 mV to -69.9 +/- 3.5 mV. Subsequently, within 6.7 +/- 2.1 min VM declined to -3.4 +/- 1.2 mV, associated with a progressive contracture. Under whole cell voltage clamp, in myocytes held at their resting potential (VM = -76.2 +/- 0.9 mV), granules induced discrete inward current steps (resembling 'single channel' activity), with a mean amplitude of -86.8 +/- 1.4 pA and open times lasting from seconds up to several minutes. The mean conductance and reversal potential calculated from the linear regression analysis of the I-V relations were 1390 pS and -6.8 mV, respectively. The probable non-selectivity of these 'channels' and the resultant loss of membrane K+ selectivity can account for the reduction in VM. At the same time, opening of these pores leads to Ca2+ overload, resulting in contracture and cell damage.

Peritoneal exudate lymphocyte and mixed lymphocyte culture hybridomas are cytolytic in the absence of cytotoxic cell proteinases and perforin

We have utilized the sensitive polymerase chain reaction (PCR) to determine whether cytotoxic T lymphocyte (CTL) hybridomas generated from peritoneal exudate lymphocytes (PEL) and mixed lymphocyte cultures (MLC) express transcripts for perforin and the cytotoxic cell proteinases CCP1 to CCP5. We could readily detect less than one transcript per cell using this methodology. Cytolytic activity could be induced to varying levels in four of the five hybridoma clones tested. With the exception of low level CCP2 expression in the MLC hybridoma MD45 following antigen stimulation, all of the hybridomas could be stimulated to function as potent cytolytic cells in the complete absence of perforin or CCP transcripts. PCR analysis utilizing actin primers indicated that all samples contained material which could be reverse transcribed and PCR-amplified. These results support the argument that populations of lymphocytes do exist that are capable of target cell lysis by an alternative mechanism not involving perforin and CCP.

Delineation of tissue damage mechanisms in experimental autoimmune encephalomyelitis (EAE). II. Characteristics of astrocyte detachment mediated by myelin basic protein (MBP) specific CD4+ T lymphocytes

We have shown that encephalitogenic, myelin basic protein (MBP)-specific CD4+ T cells can cause astrocyte and oligodendrocyte detachment in vitro. Similar processes may damage the central nervous system (CNS) in vivo by causing disorganization and destruction of brain tissue structure. The finding that 'bystander' allogeneic fibrosarcoma cells were detached by MBP-specific CD4+ T cells only when syngeneic astrocytes were present, suggested that a soluble cell-detaching factor (CDF) is released during the specific astrocyte-CD4+ effector interaction. In this study, CDF activity was detected in the supernatants of MBP-reactive CD4+ T cells incubated with concanavalin A or astrocytes. Lymphocyte-induced astrocyte lysis, but not detachment, was inhibited by the protein synthesis inhibitors, cycloheximide and puromycin, indicating that de novo protein synthesis is required for this type of lysis, but not for detachment. Astrocyte detachment was not inhibited, but rather augmented, by the trypsin inhibitors, soybean trypsin inhibitor (SBTI) and alpha-1-antitrypsin (alpha 1), suggesting that the CDF activity is not due to tryptic serine proteases, although it may be protease susceptible. The heparanase inhibitor, heparin, inhibited CD4+ T cell-mediated astrocyte detachment at low doses, but augmented detachment at higher doses, indicating that detaching activity is not due to heparanases. The actin microfilament disrupting agent, cytochalasin B (CB), inhibited astrocyte detachment induced by MBP-specific CD4+ T cells. CB pretreatment of the target astrocytes, but not of the effector CD4+ T cells, inhibited astrocyte detachment, suggesting that the integrity of the target's, but not the effector's, cytoskeleton is required for astrocyte detachment. The results herein suggest that during astrocyte interaction with MBP-specific CD4+ T cells, soluble factors are released that trigger an intrinsic astrocyte detachment mechanism.

Delineation of tissue damage mechanisms in experimental autoimmune encephalomyelitis (EAE). I. Cell detachment and lysis induced by encephalitogenic CD4+ T lymphocytes

Myelin basic protein (MBP) reactive CD4+ T lymphocytes, capable of inducing experimental autoimmune encephalomyelitis (EAE), were examined for their ability to damage target cells of central nervous system (CNS) origin. Damage was assessed by monitoring detachment of adherent astrocytes from substratum and astrocyte lysis. MBP-specific, but non-encephalitogenic CD4+ T cells mediated astrocyte detachment but not lysis. However, encephalitogenic CD4+ T cell lines were more efficient in causing astrocyte detachment and could also cause astrocyte lysis. The detachment and lytic activities of the MBP-reactive T cell lines tested were often independent of the presence of specific antigen, and were not restricted to syngeneic major histocompatibility (MHC) antigens. MBP often augmented the detaching and, if lytic, lytic activities of these T cells. The encephalitogenic CD4+ T cells also detached and lysed allogeneic 'bystander' fibroblasts in the presence of unlabelled syngeneic astrocytes, suggesting the involvement of a soluble mediator(s). Although MBP is essential for the initiation of EAE, the presence of MBP on cells of CNS origin, such as astrocytes and oligodendrocytes, does not appear to be necessary for their damage by MBP-specific CD4+ T cells. Immune CD4+ T cells, which penetrate the CNS, may disorganize brain tissue structure by lysing astrocytes directly and by damaging other brain cells indirectly by soluble mediators. Thus cellular detachment, in addition to cell lysis, mediated by MBP-specific CD4+ cells may contribute to EAE pathogenesis.

Immunological rejection of heart transplant: how lytic granules from cytotoxic T lymphocytes damage guinea pig ventricular myocytes

We investigated the mechanism by which lytic granules extracted from cytotoxic T lymphocytes (CTL) damage guinea pig ventricular myocytes in order to determine whether their actions can be related to the overall immunological rejection of the transplanted heart. Granule-induced myocyte morphological changes and final destruction were preceded by shortening of action potential duration (APD) and reductions of the resting potential and the action potential amplitude. APD shortening was probably caused by a granule-induced increase in outward current (most likely non-specific). Ryanodine, which blocks Ca2+ release from the sarcoplasmic reticulum, did not interfere with the morphological and electrophysiological effects of lytic granules. Fura-2 imaging indicated that [Ca2+]i initially increased about 2-fold from 90.0 +/- 11.5 nM, while cell length decreased less than 5% from a mean value of 99.0 +/- 9.0 microns. A further increase in [Ca2+]i (greater than 10 fold) was associated with progressive contracture and destruction, suggesting that the structural damage inflicted by lytic granules is caused by [Ca2+]i overload. The results indicate that the cytocidal action of CTL-derived lytic granules may be involved in immunologically induced damage, even to the extent of rejection of the transplanted heart.

T-cell-mediated cytotoxicity

There are two competing theories to explain the mechanism(s) by which cytolytic T lymphocytes kill target cells: granule exocytosis of a pore-forming protein, and contact-induced internal disintegration. Accumulated evidence supports alternative pathways in lymphocytoxicity, possibly reflecting distinct effector functions expressed by different killer cells and cells at different stages of activation.

Early structural changes in vascularized periosteal flaps studied in situ

This study examines the very early stages of osteogenesis in vascularized periosteal flaps and completes a characterization of their behavior after decortication. Pleuroperiosteal flaps based on the intercostal artery were developed in nine dogs and studied in situ by histologic and tetracycline fluorescence methods over periods varying from 1 to 7 days. The earliest changes were noted at 72 hours and were characterized by cellular and capillary proliferation, osteoid deposition, and bright fluorescence. The potential function of retained osseous spiculae was investigated separately. It was concluded that microscopic fragments of mature bone trapped within the flaps appear to assist and consolidate new bone formation.

The lysis of cytotoxic T lymphocytes and their blasts by cytotoxic T lymphocytes

After binding to their targets, cytotoxic T lymphocytes (CTL) deliver a lethal hit signal, ultimately leading to target cell lysis, and then can recycle to lyse additional targets, without themselves being destroyed. If non-specific secreted lytic mediators are involved in such lysis. CTL survival would not be expected unless the effectors are immune to CTL-mediated lysis. Therefore the lytic susceptibilities of alloimmune peritoneal exudate lymphocytes (PEL), containing up to 50% CTL, and of the cytolytic PEL blasts (PEB), obtained by culturing with interleukin-2 (IL-2), were examined. 51Cr-labelled BALB/c (H-2d) anti-EL4 (H-2b) (d alpha b) PEL were lysed 88%, 78%, and 48% by C3H/eb (H-2k) anti-P815 (H-2d) (k alpha d) PEL, C57BL/6 (H-2b) anti-P815 (b alpha d) PEL and b alpha d PEB, respectively. Similarly, b alpha d PEL were lysed 82% and 21% by d alpha b PEL and PEB, respectively. b alpha d PEB were lysed 82%, 28-39% and 39-51% by k alpha d PEL, b alpha d PEL and b alpha d PEB, respectively, b alpha d PEB were lysed 29-55% by d alpha b PEL. Furthermore, the CTL-containing populations were no less susceptible to lysis than normal lymphocytes. Since the majority (80-90%) of cells in these two types of CTL-containing populations can be directly and specifically lysed by appropriately immunized PEL CTL, we conclude that both the lytic granule and perforin lacking (PEL) and containing (PEB) CTL are not a priori immune to CTL-mediated lysis. These findings are in accord with theories proposing lysis to be induced by receptor-mediated contact between effector CTL and target cells, and challenge those suggesting the involvement of secreted lytic mediators.

T cell activation: independent induction of killing activity and interleukin 2 secretion in cytolytic hybridomas

Memory-like cytotoxic T lymphocytes (CTL) hybridomas exhibiting inducible killing activity and IL2 production were used to analyze the anamnestic response of CTL. Four activating agents were examined; anti-Thy-1 monoclonal antibody G7, staphylococcal enterotoxin B, interferon (IFN)-alpha/beta and IFN-gamma. These agents seemed to affect CTL activities in three distinct ways. Anti-Thy-1 monoclonal antibody, like specific antigen, was found to be a potent inducer of specific killing and IL2 production, whereas staphylococcal enterotoxin B induced IL2 production, but not cytolytic activity. On the other hand, IFN-alpha/beta and IFN-gamma effectively stimulated cytotoxicity without inducing IL2 production. The independent triggering of specific killing and IL2 secretion in the monoclonal cytolytic hybridomas suggests that in CTL distinct signals stimulate killing activity and IL2 production. The results also suggest that IFN-alpha/beta and IFN-gamma trigger the cytolytic program through an alternative activation pathway which does not involve the T cell receptor.

The cytolytic T lymphocyte and its mode of action

While the binding step of cytolytic T lymphocyte (CTL) target cell interaction resulting in conjugate formation is a well-characterized event, there seems to be more than one mechanism whereby lymphocytes kill the target. In recent years, infliction of complement (C)-like "holes" (I.D. 10-20 nm) on the target cell membrane, believed to be produced by the Ca2+-dependent lytic protein(s) perforin/cytolysin of secretory lytic granule origin has been proposed to be the mechanism of lymphocytotoxicity. More recent evidence, however, suggests that Ca2+-dependent exocytosis of lytic granules (where detectable) is not involved in lymphocyte-mediated cytolysis. Furthermore, neither formation of C-like "holes" in targets exposed to CTL, nor higher-than-background levels of lytic granules, perforin or BLT-esterases, have been detected in highly potent, peritoneal exudate CTL (PEL) derived directly from the animal or in cytocidal PEL-hybridomas. Hence exocytosis of perforin and formation of the above pores may apply to certain effector cells, particularly those grown in vitro in IL-2, but not to in vivo primed CTL such as PEL. On the other hand, work from this laboratory with Ca2+ probes has shown that lysis induced by CTL such as PEL-not involving lytic granules, perforin or formation of the above "holes"-is preceded by a marked prelytic elevation of cytosolic Ca2+ in the target. CTL-induced target cell membrane perturbation--a direct result of receptor-mediated effector-to-target interaction or through a membrane-bound or secreted effector component(s)--may be responsible for triggering the prelytic influx of Ca2+ from external sources, or its mobilization from internal stores in the target. We propose that CTL-induced, persistent elevation of cytosolic Ca2+, above a critical level, rather than formation of 10-20 nm pores, is responsible for the catastrophic prelytic events observed in the target, such as bleb formation, metabolic exhaustion and DNA degradation, ultimately leading to lysis.