Influence of pro-inflammatory (IL-1 alpha, IL-6, TNF-alpha, IFN-gamma) and anti-inflammatory (IL-4) cytokines on chondrocyte function

Chondrocyte death by apoptosis is associated with cartilage matrix degradation

OBJECTIVES

To investigate the frequency of chondrocyte apoptosis in equine articular cartilage (AC) specimens and to examine the relationship between the process of cell death and the degree of cartilage degradation using a direct quantification of numbers of apoptotic cells and expression of active caspase-3.

METHODS

AC from equine metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints was used and each joint was graded macroscopically for cartilage degradation (macroscopic osteoarthritis (OA) score). Cartilage sections were graded using a 'modified' Mankin scoring system. Apoptosis of chondrocytes in cartilage sections was assessed morphologically by appearance of apoptotic features (direct method) and by expression of active caspase-3 using indirect immunohistochemistry.

RESULTS

The extent of apoptosis assessed by the direct method did not show any relationship with increasing severity of OA (P=0.72). However, there was a significant positive correlation between 'modified' Mankin score and apoptosis determined by caspase-3, with the extent of apoptosis found to increase linearly with increasing severity of OA (r=0.44, P=0.0043). Caspase-3 expression was found to be significantly higher in the superficial and middle zones than in the deep zone (P<0.001). In the superficial, middle and deep zones, expression of caspase-3 was significantly higher in the MCP joint than in the PIP joint (P=0.013, P=0.0018 and P=0.029, respectively). Within the MCP joints, apoptosis was higher in the lateral compartment compared to the medial (P=0.053).

CONCLUSIONS

The data presented in this study demonstrate that chondrocyte apoptosis is positively associated with degree of cartilage matrix damage and that the extent of apoptosis varies with cartilage zones and mechanical loading environment of the joint.

Cellular events leading to chondrocyte death after cartilage impact injury

OBJECTIVE

We undertook this study to test our postulate that leukocytes extend the zone of injury in cartilage after acute mechanical trauma.

METHODS

Fresh cadaveric canine femoral condyles were subjected to 20-25-MPa impact injury. Condyle explants or dispersed chondrocytes were cultured with autologous blood mononuclear leukocytes (MNLs). Viability of chondrocytes at varying distances from the impact site was assessed by trypan blue exclusion.

RESULTS

Mechanical injury caused a significant loss of viable chondrocytes over 7 days, even in cartilage >10 mm from the impact site. After biomechanical stress, death of cells within 10 mm of the impact could be largely prevented by addition of N(G)-monomethyl-L-arginine to inhibit nitric oxide (NO) generation. Chondrocytes within 10 mm of the impact were also susceptible to killing by living MNLs, but not by incubation with the supernatants of endotoxin-activated MNLs. Chondrocytes in this vulnerable zone expressed intercellular adhesion molecule 1 (ICAM-1) (CD54), facilitating attachment of MNLs that localized adjacent to the chondrocytes. Leukocytes killed dispersed chondrocytes harvested from the impact zone by generation of reactive oxygen species. Leukocyte-mediated killing could be blocked by desferoxamine or by antibodies to CD18, which prevent attachment of leukocytes to ICAM-1-expressing chondrocytes.

CONCLUSION

Our data suggest that after mechanical injury, chondrocytes distant from the site may be killed through the generation of NO. Inflammatory leukocytes further extend the zone of chondrocyte death by adhering to chondrocytes expressing ICAM-1 and by inducing the accumulation of free oxygen radicals in the chondrocyte cytoplasm. Patients may benefit from therapies that reduce infiltration of inflammatory leukocytes into acutely injured cartilage.

Gross, histologic, and gene expression characteristics of osteoarthritic articular cartilage of the metacarpal condyle of horses

OBJECTIVE

To identify patterns and correlations of gross, histologic, and gene expression characteristics of articular cartilage from horses with osteoarthritis.

ANIMALS

10 clinically normal horses and 11 horses with osteoarthritis of the metacarpal condyles.

PROCEDURES

Metacarpophalangeal joints were opened and digitally photographed, and gross lesions were scored and quantified. Representative cartilage specimens were stained for histologic scoring. Total RNA from dorsal and palmar articular surfaces was processed on an equine gene expression microarray.

RESULTS

Histologic scores were greater in both regions of osteoarthritic joints, compared with corresponding regions in control joints. Cartilage from the palmar aspect of diseased joints had the highest histologic scores of osteoarthritic sites or of either region in control joints. A different set of genes for dorsal and palmar osteoarthritis was identified for high and low gene expression. Articular cartilage from the dorsal region had surface fraying and greater expression of genes coding for collagen matrix components and proteins with anti-apoptotic function, compared with control specimens. Articular cartilage from the palmar region had greater fraying, deep fissures, and less expression of genes coding for glycosaminoglycan matrix formation and proteins with anti-apoptotic function, compared with cartilage from disease-free joints and the dorsal aspect of affected joints.

CONCLUSIONS AND CLINICAL RELEVANCE

Metacarpal condyles of horses with naturally occurring osteoarthritis had an identifiable and regional gene expression signature with typical morphologic features.

Sphingosine-1-phosphate stimulates rat primary chondrocyte proliferation

Rat primary chondrocytes express the sphingosine-1-phosphate (S1P) receptor, S1P(2), S1P(3), S1P(4), but not S1P(1). When chondrocytes were stimulated with S1P or phytosphingosine-1-phosphate (PhS1P, an S1P(1)- and S1P(4)-selective agonist), phospholipase C-mediated cytosolic calcium increase was dramatically induced. S1P and PhS1P also stimulated two kinds of mitogen-activated protein kinases, extracellular signal-regulated kinase (ERK) and p38 kinase in chondrocytes. In terms of the two phospholipids-mediated functional modulation of chondrocytes, S1P and PhS1P stimulated cellular proliferation. The two phospholipids-induced chondrocyte proliferations were almost completely blocked by PD98059 but not by SB203580, suggesting that ERK but not p38 kinase is essentially required for the proliferation. Pertussis toxin almost completely inhibited the two phospholipids-induced cellular proliferation and ERK activation, indicating the crucial role of G(i) protein. This study demonstrates the physiological role of two important phospholipids (S1P and PhS1P) on the modulation of rat primary chondrocyte proliferation, and the crucial role played by ERK in the process.

Innervation, inflammation, and hypermobility may characterize pathologic disc degeneration: review of animal model data

Animal models provide important clues to the pathomechanisms of human intervertebral disc degeneration. Previous reviews on this topic have highlighted the fact that loss of nuclear volume (and, consequently, pressure) is a common trigger for tissue-remodeling and anatomic change consistent with degeneration in humans. Unfortunately, a large gap still exists in the medical knowledge base that serves to distinguish symptomatic from asymptomatic degeneration. Because disc degeneration per se is not a basis for clinical intervention, identification of specific features underlying discogenic pain is of the utmost importance to advance the current level of care and identify novel therapeutic targets. This article presents animal-model evidence that pathologic, or painful, degeneration is characterized by ineffective injury-healing of peripheral tissue. Because the disc is only vascularized at the vertebral end plate and the outer part of the anulus, these are the likely sites for focal damage, inflammation, neoinnervation, and nociceptor sensitization. Consequently, while nuclear insufficiency is likely the root of degenerative change, the end plate and peripheral part of the anulus are more likely the source of patient discomfort.

Carboxymethyl-chitosan protects rabbit chondrocytes from interleukin-1beta-induced apoptosis

Chondrocyte apoptosis is important in pathogenesis of osteoarthritis. Chitosan is a non-toxic, biodegradable and biocompatible glycosaminoglycan. In this study, the effects of carboxymethyl-chitosan (CM-chitosan), a soluble derivative of chitosan, on chondrocyte apoptosis were investigated. Primary rabbit chondrocytes were cultured and induced to apoptosis by 10 ng/ml interleukin-1beta (IL-1beta). After treatment with various concentrations of CM-chitosan (50, 100, 200 microg/ml), the apoptotic rate, mitochondrial function, nitric oxide production, and the levels of inducible nitric oxide synthase (iNOS) mRNA and reactive oxygen species in IL-1beta-induced chondrocytes were examined. The results showed that CM-chitosan could inhibit chondrocyte apoptosis in a dose-dependent manner. Furthermore, it could partly restore the levels of mitochondrial membrane potential and ATP, decrease nitric oxide production by down-regulation of iNOS mRNA expression, and scavenge reactive oxygen species in chondrocytes induced by IL-1beta. The results suggested that the inhibitory effects of CM-chitosan on IL-1beta-induced chondrocyte apoptosis were possibly due to the protection of mitochondrial function, the decline in the levels of nitric oxide and reactive oxygen species.

Polyamine depletion inhibits apoptosis following blocking of survival pathways in human chondrocytes stimulated by tumor necrosis factor-alpha

Chondrocyte apoptosis can be an important contributor to cartilage degeneration, thereby making it a potential therapeutic target in articular diseases. To search for new approaches to limit chondrocytic cell death, we investigated the requirement of polyamines for apoptosis favored by tumor necrosis factor-alpha (TNF), using specific polyamine biosynthesis inhibitors in human chondrocytes. The combined treatment of C-28/I2 chondrocytes with TNF and cycloheximide (CHX) resulted in a prompt effector caspase activation and internucleosomal DNA fragmentation. Pre-treatment of chondrocytes with alpha-difluoromethylornithine (DFMO), an ornithine decarboxylase (ODC) inhibitor, markedly reduced putrescine and spermidine content as well as the caspase-3 activation and DNA fragmentation induced by TNF and CHX. DFMO treatment also inhibited the increase in effector caspase activity provoked by TNF plus MG132, a proteasome inhibitor. DFMO decreased caspase-8 activity and procaspase-8 content, an apical caspase essential for TNF-induced apoptosis. Although DFMO increased the amount of active, phosphorylated Akt, inhibitors of the Akt pathway failed to restore the TNF-induced increase in caspase activity blunted by DFMO. DFMO also reduced the increase in caspase activity induced by staurosporine, but in this case Akt inhibition prevented the DFMO effect. Pre-treatment with CGP 48664, an S-adenosylmethionine decarboxylase (SAMDC) inhibitor markedly reduced spermidine and spermine levels, and provoked effects similar to those caused by DFMO. Finally DFMO was effective even in primary osteoarthritis (OA) chondrocyte cultures. These results suggest that the intracellular depletion of polyamines in chondrocytes can inhibit both the death receptor pathway by reducing the level of procaspase-8, and the apoptotic mitochondrial pathway by activating Akt.

An antioxidative and antiinflammatory agent for potential treatment of osteoarthritis from Ecklonia cava

Osteoarthritis is thought to be induced by the ageing-related loss of homeostatic balance between degeneration and repair mechanism around cartilage tissue in which inflammatory mediators such as reactive oxygen species, cytokines and prostaglandins are prone to over-production under undesirable physiological conditions. Phlorotannins are unique polyphenolic compounds bearing dibenzo-1,4-dioxin skeleton which are not found in terrestrial plants but found only in some brown algal species such as Ecklonia and Eisenia families. Phlorotannin-rich extracts of Ecklonia cava including LAD103 showed significant antioxidant activities such as DPPH radical scavenging, ferric ion reduction, peroxynitrite scavenging, and inhibition of LDL oxidation, indicating their possible antioxidative interference both in onset and downstream consequences of osteoarthritis. LAD103 also showed significant down regulation of PGE2 generation in LPS-treated RAW 246.7 cells, and significant inhibition of human recombinant interleukin-1alpha-induced proteoglycan degradation, indicating its beneficial involvement in pathophysiological consequences of osteoarthritis, the mechanism of which needs further investigation. Since LAD103 showed strong therapeutic potentials in arthritic treatment through several in vitro experiments, it is highly encouraged to perform further mechanistic and efficacy studies.

Anti-inflammatory effects of IL-4 and dynamic compression in IL-1β stimulated chondrocytes

Mechanical loading can counteract inflammatory pathways induced by IL-1beta by inhibiting *NO and PGE2, catabolic mediators known to be involved in cartilage degradation. The current study investigates the potential of dynamic compression, in combination with the anti-inflammatory cytokine, IL-4, to further abrogate the IL-1beta induced effects. The data presented demonstrate that IL-4 alone can inhibit nitrite release in the presence and absence of IL-1beta and partially reverse the IL-1beta induced PGE2 release. When provided in combination, IL-4 and dynamic compression could further abrogate the IL-1beta induced nitrite and PGE2 release. IL-1beta inhibited [3H]thymidine incorporation and this effect could be reversed by IL-4 or dynamic strain alone or both in combination. By contrast, 35SO4 incorporation was not influenced by IL-4 and/or dynamic strain in IL-1beta stimulated constructs. IL-4 and mechanical loading may therefore provide a potential protective mechanism for cartilage destruction as observed in OA.

Interleukin-1beta induces death in chondrocyte-like ATDC5 cells through mitochondrial dysfunction and energy depletion in a reactive nitrogen and oxygen species-dependent manner

IL-1 (interleukin-1) acts as a key mediator of the degeneration of articular cartilage in RA (rheumatoid arthritis) and OA (osteoarthritis),where chondrocyte death is observed. It is still controversial, however, whether IL-1 induces chondrocyte death. In the present study, the viability of mouse chondrocyte-like ATDC5 cells was reduced by the treatment with IL-1beta for 48 h or longer. IL-1beta augmented the expression of the catalytic gp91 subunit of NADPH oxidase, gp91phox, as well as inducible NO synthase in ATDC5 cells. Generation of nitrated guanosine and tyrosine suggested the formation of reactive nitrogen species including ONOO- (peroxynitrite), a reaction product of NO and O2-, in ATDC5 cells and rat primary chondrocytes treated with IL-1beta. Death of ATDC5 cells after IL-1beta treatment was prevented by an NADPH-oxidase inhibitor, AEBSF[4-(2-aminoethyl)benzene-sulphonyl fluoride], an NO synthase inhibitor, L-NAME (NG-nitro-L-arginine methyl ester), and a ONOO- scavenger, uric acid. The viability of ATDC5 cells was reduced by the ONOO(-)-generator 3-(4-morpholinyl)sydnonimine hydrochloride, but not by either the NO-donor 1-hydroxy-2-oxo-3-(N-methyl-2-aminopropyl)-3-methyl-1-triazene or S-nitrosoglutathione. Disruption of mitochondrial membrane potential and ATP deprivation were observed in IL-1beta-treated ATDC5 cells, both of which were restored by L-NAME, AEBSF or uric acid. On the other hand, no morphological or biochemical signs indicating apoptosis were observed in these cells. These results suggest that the death of chondrocyte-like ATDC5 cells was mediated at least in part by mitochondrial dysfunction and energy depletion through ONOO- formation after IL-1beta treatment.

Lysophosphatidic acid stimulates cell proliferation in rat chondrocytes

Rat primary chondrocytes express the lysophosphatidic acid (LPA) receptor, LPA1, LPA3, but not LPA2. When chondrocytes were stimulated with LPA, phospholipase C-mediated cytosolic calcium increase was dramatically induced. LPA also stimulated two kinds of mitogen-activated protein kinase, extracellular signal-regulated kinase (ERK) and p38 kinase in chondrocytes. In terms of the LPA-mediated functional modulation of chondrocytes, LPA stimulated cellular proliferation. We examined the signaling pathways involved in LPA-mediated cellular proliferation. LPA-induced chondrocyte proliferation was almost completely blocked by 2'-amino-3'-methoxyflavone (PD98059) but not by 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), suggesting that ERK activity is essentially required for the process. Pertussis toxin almost completely inhibited the LPA-induced cellular proliferation and ERK activation, indicating the role of G(i/o) protein(s) in the processes. This study demonstrates the physiological role of LPA on the modulation of rat primary chondrocyte proliferation, and the crucial role played by ERK in the process.

Tumor necrosis factor-alpha modulates matrix production and catabolism in nucleus pulposus tissue

STUDY DESIGN

This study examines changes in the production of extracellular matrix molecules as well as the induction of tissue degradation in in vitro formed nucleus pulposus (NP) tissues following incubation with tumor necrosis factor (TNF)alpha.

OBJECTIVE

To characterize the response of NP cells to TNF-alpha, a proinflammatory cytokine present in herniated NP tissues.

SUMMARY OF BACKGROUND DATA

TNF-alpha is a proinflammatory cytokine expressed by NP cells of degenerate intervertebral discs. It is implicated in the pain associated with disc herniation, although its role in intervertebral disc degeneration remains poorly understood.

METHODS

In vitro formed NP tissues were treated with TNF-alpha (up to 50 ng/mL) over 48 hours. Tissues were assessed for histologic appearance, proteoglycan and collagen contents, as well as proteoglycan and collagen synthesis. Reverse transcriptase polymerase chain reaction was used to determine the effect of TNF-alpha on NP cell gene expression. Proteoglycan degradation was assessed by immunoblot analysis.

RESULTS

At doses of 1-5 ng/mL, TNF-alpha induced multiple cellular responses, including: decreased expression of both aggrecan and type II collagen genes; decreases in the accumulation and overall synthesis of aggrecan and collagen; increased expression of MMP-1, MMP-3, MMP-13, ADAM-TS4, and ADAM-TS5; and induction of ADAM-TS dependent proteoglycan degradation. Within 48 hours, these cellular responses resulted in NP tissue with only 25% of its original proteoglycan content.

CONCLUSIONS

Because low levels of TNF-alpha, comparable to those present physiologically, induced NP tissue degradation, this suggests that TNF-alpha may contribute to the degenerative changes that occur in disc disease.

Influence of bisphosphonates on the production of pro-inflammatory cytokines by activated human articular chondrocytes

Bisphosphonates have anti-inflammatory effects in rheumatoid arthritis and chondroprotective effects in animal arthritis models but their influence on chondrocytes is not known. The aim of this study is to investigate whether bisphosphonates could influence the production of pro-inflammatory cytokines by activated chondrocytes. Therefore human articular cartilage explants were incubated at 48 h with clodronate, pamidronate or risedronate (10(-6) and 10(-8)mol/L), and dexamethasone (10(-8)mol/L). Subsequently, cultures were stimulated with IL-1, 10 ng/mL (n=6) or 1 ng/mL (n=10) for 48 h. Co-incubation was performed with or without bisphosphonates or dexamethasone. A flow cytometric microsphere-based immunoassay was used for the detection of the pro-inflammatory cytokines IL-6, IL-8, TNF-alpha, IL-1 and the regulatory cytokines IL-12p70 and IL-10 in the supernatants. Stimulation with IL-1 resulted in a dose dependent induction of IL-6 and IL-8, but no production of the other cytokines could be demonstrated. This production of IL-6 and IL-8 was neither inhibited nor enhanced by bisphosphonates. Only dexamethasone caused an inhibition of IL-6 production. In conclusion, there is no evidence on the level of articular cartilage cells that bisphosphonates would suppress or enhance IL-6 and IL-8 mediated joint destruction.

Retinoic acid blocks pro-inflammatory cytokine-induced matrix metalloproteinase production by down-regulating JNK-AP-1 signaling in human chondrocytes

The development of osteoarthritis (OA) has recently been implicated as a result of immune-mediated damage of chondrocytes and their supporting matrixes. Pro-inflammatory cytokines like interleukin (IL)-1 and tumor necrosis factor alpha (TNF-alpha) play pivotal roles in immunopathogenesis of OA. Because vitamins preserving anti-oxidative effects are suggested to provide protection in OA patients from joint damage, in the present study, we examined the effects and mechanisms of all-trans retinoic acid (t-RA) in suppressing pro-inflammatory cytokine-induced matrix metalloproteinases (MMPs) production in human chondrocytes. Chondrocytes were prepared from cartilage specimens of OA patients receiving total hip or total knee replacement. The protein concentration was measured by ELISA, the mRNA expression by reverse transcriptase-polymerase chain reaction, the protein expression by Western blotting, the transcription factor DNA-binding activity by electrophoretic mobility shift assay and the protein kinase activity by kinase assay. We showed that both MMP-1 and MMP-13 mRNA expression, protein production and enzyme activity induced by either IL-1 or TNF-alpha were suppressed by t-RA or different retinoid derivatives. The molecular investigation revealed that the t-RA-mediated suppression was likely through blocking p38 kinase and c-Jun N-terminal kinase-activator protein-1 signaling pathways. In contrast, t-RA had no effect on extracellular signal-regulated kinase activity, nuclear factor (kappa)B (NF-(kappa)B) DNA-binding activity and I(kappa)B(alpha) degradation. Furthermore, we showed that t-RA could reduce IL-1-induced TNF-alpha production in chondrocytes. Our results suggest that vitamin A may protect OA patients from pro-inflammatory cytokine-mediated damage of chondrocytes and their supporting matrixes.

Dose-Dependent Modulation of the In Vitro Cytokine Production of Human Immune Competent Cells by Lead Salts

Lead pollution constitutes a major health problem that has been intensively debated. To reveal its effects on the immune response, the influence of lead on the in vitro cytokine production of human peripheral mononuclear blood cells was investigated. Isolated cells were exposed to lead acetate or lead chloride for 24 h in the presence of either heat-killed Salmonella enteritidis (hk-SE) or monoclonal antibodies (anti-CD3, anti-CD28, anti-CD40) as cell activators. Our results showed that while higher lead doses are toxic, lower ones evoke immunomodulatory effects. All tested lead doses significantly reduced cell vitality and/or proliferation and affected secretion of proinflammatory, T helper cell type (T(H))1 and T(H)2 cytokines. Expression of interferon (IFN)-gamma, interleukin (IL)-1beta, and tumor necrosis factor (TNF)-alpha was reduced at lower lead doses in both models of cell stimulation. Although hk-SE failed to induce detectable IL-4 levels, monoclonal antibody-induced IL-4, IL-6, and IL-10 secretion increased in the presence of lower lead doses. Also, levels of hk-SE-induced IL-10 and IL-6 secretion were increased at lower lead doses. Thus, exposure to lower doses leads to suppression of the T(H)1 cytokine IFN-gamma and the proinflammatory cytokines TNF-alpha and IL-1beta. The elevated production of IL-4 and/or IL-10 can induce and maintain a T(H)2 immune response and might contribute to increased susceptibility to pathologic agents as well as the incidence of allergic hypersensitivity and/or T(H)2-dominated autoimmune diseases.

Acute CD4+ T lymphocyte-dependent interleukin-1-driven arthritis selectively requires interleukin-2 and interleukin-4, joint macrophages, granulocyte-macrophage colony-stimulating factor, interleukin-6, and leukemia inhibitory factor

OBJECTIVE

To further investigate the effects of interleukin-1 (IL-1) in immune-mediated joint inflammation, we examined the role of IL-2, Th1 interferon-gamma (IFNgamma), and Th2 (IL-4) cytokines, joint macrophages, and macrophage-derived cytokines (IL-12 p40, IL-6, leukemia inhibitory factor [LIF], oncostatin M [OSM], and granulocyte-macrophage colony-stimulating factor [GM-CSF]) in a CD4+ T lymphocyte-dependent model of acute arthritis.

METHODS

Methylated bovine serum albumin (mBSA)/IL-1-induced arthritis was elicited in wild-type, gene-knockout, and monoclonal antibody-treated mice. Synovial lining macrophages were selectively depleted by intraarticular injection of clodronate liposomes prior to disease induction. The severity of arthritis was assessed histologically.

RESULTS

Mice deficient in IL-2 were almost completely protected from arthritis, and neutralization of IL-4 reduced the severity of disease. In contrast, arthritis severity and resolution appeared to be independent of IFNgamma. Synovial lining macrophage depletion markedly reduced arthritis severity. IL-6 or LIF deficiency was only modestly protective, although as previously reported, GM-CSF deficiency conferred profound disease resistance. IL-12 p40-deficient mice (which lack IL-12 and IL-23) and OSM receptor-deficient mice were susceptible to mBSA/IL-1-induced arthritis.

CONCLUSION

Acute mBSA/IL-1-induced arthritis is dependent on IL-2 and IL-4, but not IFNgamma. In vivo, the Th1/Th2 paradigm may be distorted by the presence of macrophage-derived cytokines such as IL-1. Synovial lining macrophages are essential in mBSA/IL-1-induced arthritis. However, the requirement for macrophage-derived cytokines is selective; that is, IL-6, LIF, and especially GM-CSF are necessary, but IL-12, IL-23, and OSM are dispensable. IL-1 may therefore influence both adaptive and innate immune mechanisms in acute inflammatory arthritis.

Chondrosarcoma cell differentiation

A mixed population of lymphocytes from a healthy donor co-existed with an established culture of allogeneic chondrosarcoma cells, during which time the tumor cells changed from malignantly transformed to benign fibroblast-like morphology; from multilayered to a monolayered growth pattern; lost their potency to grow in colonies in soft agar; and showed signs of senescence. A discussion of possible molecular mechanisms for this event is offered. If there are as yet undiscovered lymphokines that can induce reversal of the malignant geno/phenotype, the cognate gene(s) should be cloned for genetic engineering and for the mass production of the corresponding molecular mediators for clinical trials.