Reduction of heat-shock protein-70 after prolonged treatment with retinoids: biological and clinical implications

Heat shock proteins (HSPs) are a group of highly conserved polypeptides involved in cellular response to heat or other physical or chemical stresses. It has been recently reported that HSPs could play a role in cellular differentiation. In this study we have evaluated, by a cytofluorimetric method, the presence of HSP-70 in HL-60 cells during treatment with all-trans retinoic acid (ATRA), 9-cis retinoic acid (9-cis RA), and 13-cis retinoic acid (13-cis RA). After 1 and 3 days of incubation at 10(-7) M, HSP-70 did not show any variation compared to control; prolonging the exposure, together with the appearance of cellular differentiation along the granulocytic pathway and apoptosis, a progressive decrease of HSP-70 was observed that, after 8 days of treatment, was reduced by 40% with ATRA and by 28% with 9-cis RA compared to untreated samples, while only minimal changes were evident by incubating the cells with 13-cis RA. Reduction of HSP-70 was not associated with decreased protein synthesis, as demonstrated by [3H] leucine incorporation. Double labeling with propidium iodide showed a decrease in HSP-70 in all the phases of the cell cycle concomitant with a reduced percentage of cycling cells in ATRA-treated samples. Dot blot and Northern blot analysis demonstrated no change in HSP-70 mRNA after retinoid treatment, thus suggesting a post-transcriptional regulation of the phenomenon. This reduced production of HSP-70 caused by ATRA and by 9-cis RA, though to a lesser extent, could render the cells more sensitive to cytotoxic agents and could provide the rationale for the efficacy of ATRA + chemotherapy combinations.

Adenoviral mediated gene transfer can be accomplished in human myeloid cell lines and is inhibited by all-trans retinoic acid-induced differentiation

BACKGROUND AND OBJECTIVE

Gene transfection could potentially represent a useful therapeutic tool for genetic and neoplastic hematological diseases. After having long been considered poorly able to transfect myeloid cells, adenoviral vectors have recently been demonstrated to be capable of introducing foreign DNA into purified CD34+ cells from human bone marrow or cord blood. In the present study we evaluated the feasibility of adenoviral-mediated gene transfer in two human leukemic cell lines, both at baseline and after differentiation induction by all-trans retinoic acid (ATRA).

METHODS

We used a recombinant adenovirus expressing beta-galactosidase (Ad-RSV-beta-gal) to transfect K562 and HL-60 cell lines. The effects of 10(-6)M ATRA were evaluated after 8 days of exposure. The efficacy of transfection was verified by X-gal staining.

RESULTS

Ad-RSV-beta-gal was able to transfect both the HL-60 and, to a minor extent, the K562 cell lines. The addition of ATRA had no effect on transfection of K562 cells, while a lower percentage of beta-gal-positive cells was detected in HL-60, which underwent differentiation upon ATRA treatment.

INTERPRETATION AND CONCLUSIONS

These data suggest that adenoviral-mediated gene transfer could be feasible in myeloid leukemia cell lines and that it is inhibited by ATRA in differentiation-sensitive cells. The latter effect merits further investigation in order to verify whether this represents an ATRA-related or a differentiation-related phenomenon.

Opiate signaling regulates microglia activities in the invertebrate nervous system

1. Evidence supporting the presence in the invertebrate nervous system of a class of glial cells resembling vertebrate microglia was obtained in the freshwater snail Planorbarius corneus. These cells are easily identified by their immunopositivity to anti-pro-opiomelanocortin (POMC)-derived peptide antibodies. 2. Invertebrate microglia, as in vertebrates, exhibit macrophage-like activity in vivo and in cell cultures. These cells respond to the trauma of ganglionic excision and their organotypic culture by leaving their location around neurons and moving to the lesion site from which they migrate in the culture dish. 3. In vitro, these microglia undergo conformational changes and show phagocytic properties in the presence of bacteria or lipopolysaccharide. The activated cells also express tumor necrosis factor-alpha-like material and an increase in nitric oxide synthase, as shown by immunocytochemistry. 4. The inhibitory effect of morphine on the mobility and phagocytic activity of invertebrate microglia provide additional functional evidence for a possible role of opiate-like compounds in downregulating immunoregulatory processes, as also observed in the circulating immunocytes.

Loxoribine affects fludarabine activity on freshly isolated B-chronic lymphocytic leukemia cells

Purine analogues like fludarabine have been shown to be superior to conventional therapy for B-cell chronic lymphocytic leukemia (B-CLL). In order to improve the activity of fludarabine, we tested its combination with loxoribine, a guanine ribonucleotide derivative, known to enhance the sensitivity of B-CLL cells to cytotoxic drugs. B-CLL cells from 6 patients were studied; co-incubation with loxoribine 100 microM increased the activity of fludarabine by 12% to 48%, as demonstrated by XTT colorimetric assay; while 1000 microM loxoribine exerted a protective effect. Accordingly, fludarabine-induced apoptosis was enhanced by the addition of loxoribine 1000 microM (39% increase). These results indicate that the combination of loxoribine and fludarabine could be of interest in B-CLL.

Effects of homoharringtonine alone and in combination with alpha interferon and cytosine arabinoside on 'in vitro' growth and induction of apoptosis in chronic myeloid leukemia and normal hematopoietic progenitors

Homoharringtonine (HHT) is a cephalotaxine alkaloid that showed clinical efficacy in the chronic phase of chronic myeloid leukemia (Ph1+CML). As a single agent, it resulted in effectively controlling leukocytosis and in producing sporadic karyotypic conversions; its clinical use in combination with interferon (IFN-alpha) for the treatment of CML could thus be considered. In this study we evaluated the growth inhibition and the induction of apoptosis determined by HHT alone and in combination with IFN-alpha and cytosine arabinoside (Ara-C) on normal and CML (both in chronic, CML-CP and in blastic phase; CML-BP) hematopoietic progenitors. HHT is able to determine a dose-dependent cell growth inhibition; evaluation of cytotoxic activity on semisolid cultures showed an activity significantly higher on CML-CP than on normal cells (P = 0.02 for HHT 50 ng/ml and P = 0.01 for HHT 200 ng/ml). HHT exerted a synergistic effect with IFN-alpha, Ara-C and IFN-alpha + Ara-C in inhibiting CML-CP colony growth; the same activity was demonstrated by the combination of HHT with Ara-C and by the triple combination, but not by HHT + IFN-alpha, on normal myeloid progenitors. The triple combination only was able to exert a synergistic effect in CML-BP. The induction of apoptosis resulted HHT dose-dependent in CML-CP and normals; at higher drug concentrations (100-200-1000 ng/ml), HHT induced a significant increase of apoptotic cells (for normals: P = 0.04, P = 0.02 and P = 0.04; for CML-CP: P = 0.01, P = 0.01 and P = 0.04, respectively); no significant changes were observed in CML-BP. In conclusion, the differences in cytotoxic effect and apoptosis induction observed, depending on the various phases of CML, add experimental evidence to the different clinical results between the chronic phase, where the clone is responsive to HHT, and the acute phase, where the drug is ineffective. The in vitro synergism of HHT with Ara-C and IFN-alpha in CML-CP suggests further evaluation in the clinical setting.

The expression of proliferation and quiescence associated antigens in acute myeloid leukemia correlates with survival duration: analysis of 15 refractory cases

In this study, blast cells from 15 patients with acute myeloid leukemia resistant to induction therapy were examined with two monoclonal antibodies that identify, respectively, the nuclear protein specifically expressed in non proliferating cells (statin) and the proliferating cell nuclear antigen (PCNA). We found that statin values varied widely, ranging from 0.6% to 14.7% (mean value 6.4%). When the patients were subdivided according to the mean value, those presenting with higher statin values survived for a shorter period of time than the ones characterized by lower levels (p = 0.003). We observed a wide variation in the range of PCNA values; however, if an agreement between survival duration and at least one of the proposed markers was considered, all but one case displayed concordance between survival duration and PCNA and/or statin values (in addition, 4/15 cases showed agreement for both markers). These preliminary data could indicate a possible discriminating prognostic factor between categories of patients characterized by different aspects of resistance, perhaps susceptible to different salvage therapy approaches.

Effect of PDGF and TGF-beta on the release of biogenic amines from invertebrate immunocytes and their possible role in the stress response

PDGF-AB and TGF-beta 1 intervene in molluscan stress response, the former inhibiting and the latter inducing the release of norepinephrine and epinephrine from hemocytes. These amines are down-regulated even when TGF-beta 1 is added to hemolymph pre-incubated with PDGF-AB. The opposite behaviour is observed if the growth factors are reversed. The dopamine response is not affected in either case, even after the addition of CRH or ACTH. After pre-incubation with PDGF-AB or TGF-beta 1 in the presence of CRH or ACTH, norepinephrine and epinephrine release falls. These findings suggest that when the interaction is between growth factors, the order of combination is crucial, while in cases where the interaction is between growth factors and other peptides, such as CRH and ACTH, the order is of no importance.

Evolution of neuroendocrine thymus: studies on POMC-derived peptides, cytokines and apoptosis in lower and higher vertebrates

In previous papers, we showed that neuroendocrine cells reactive to anti-POMC-derived peptides and cytokines are present in the thymus of a fish and an anuran amphibian. Here we report that this phenomenon is general, as neuroendocrine cells positive to anti-POMC-derived peptides (ACTH, beta-endorphin, alpha-MSH) and cytokines (IL-1 alpha, IL-2, IL-6, TNF-alpha) are also present in the thymus of chicken and rat. However, the number and the intrathymic localization and distribution of these cells varies in the different species examined. An analysis of apoptotic cells or cells involved in apoptosis, such as interdigitating cells and macrophages, in fish, frog, chicken and rat thymus, using an immunocytochemical method and anti-DNA mAb conjugated with peroxidase (anti-DNA-POD), showed that cells positive to anti-DNA-POD mAb are present in the same thymic areas in which POMC-derived peptides and cytokines were found. In conclusion, these data on apoptotic cells in the thymus of lower and higher vertebrates are compatible with the hypothesis that neuroendocrine cells might play a role in the selection and apoptosis of thymic lymphocytes, a phenomenon which could vary slightly in different species and taxa.

Neutral endopeptidase-24.11 (NEP)-like activity in molluscan hemocytes

Using a spectrofluorimetric procedure, we found that the plasma membrane from hemocytes of two freshwater snails, Planorbarius corneus and Viviparus ater, shows neutral endopeptidase-24.11 (NEP)-like activity. Moreover, the addition of ACTH(1-24) to the hemolymph provokes an increase in NEP-like activity. This increased NEP-like activity is blocked by phosphoramidon, a potent inhibitor of mammalian NEP. These findings suggest that this peptidase has been well conserved in the course of evolution and plays an important role in immune-neuroendocrine mechanisms.

Pro-opiomelanocortin-derived peptides, cytokines, and nitric oxide in immune responses and stress: an evolutionary approach

In vertebrates, including man, the study of stress has contributed substantially to unravelling the complex relationship between immune-neuroendocrine interactions and the systems involved. On the basis of data on the presence and distribution of the main actors (POMC products, cytokines, biogenic amines, and steroid hormones) in different species and taxa from invertebrates to vertebrates, we argue that these responses have been deeply connected and interrelated since the beginning of life. Moreover, the study of nitric oxide suggests that the inflammatory reaction is located precisely between the immune and stress responses, sharing the same fundamental evolutionary roots. The major argument in favor of this hypothesis is that the immune, stress, and inflammation responses appear to be mediated by a common pool of molecules that have been conserved throughout evolution and that from a network of adaptive mechanisms. One cell type, the macrophage, appears to emerge as that most capable of supporting this network critical for survival; it was probably a major target of selective pressure. All these data fit the unitarian hypothesis we propose, by which evolution favors what has been conserved, rather than what has changed, as far as both molecules and functions are concerned.

Presence of casein immunoreactive epitopes in molluscs, fish and frog

The presence of a group of peptides derived from milk proteins (caseins) was examined by immunocytochemistry in various tissues from invertebrates and lower vertebrates. Phagocytic hemocytes from different species of molluscs, and cells located in the intestine wall or in related glands of invertebrates and lower vertebrates showed immunoreactivity to antibodies to whole casein and related fragments. Several functional tests (cell migration, inhibition test, phagocytosis) using these peptides were performed on the mollusc hemocytes. Only ovine caseinoglycopeptide was able to increase the phagocytic activity of the hemocytes towards bacteria.

Induction of ACTH- and TNF-alpha-like molecules in the hemocytes of Calliphora vomitoria (Insecta, Diptera)

Three basic cell types are described in the hemolymph of newly enclosed adult Calliphora vomitoria: prohemocytes, plasmatocytes, and granular cells. In addition, anucleate cellular fragments with some inclusions are observed. Cell division is found only in the prohemocytes. Plasmatocytes and granular cells are capable of in vitro bacterial phagocytosis and take part in capsule formation. Adrenocorticotropin hormone (ACTH)-like molecules are found in both cell types. The staining of the plasmatocytes is related to the functional activation of the cells. Indeed, positive staining is only observed during capsule formation, suggesting an induction of ACTH expression. The behaviour of tumor necrosis factor (TNF)-alpha-like molecules is similar. In conclusion, these data provide further support for the close, evolutionary relationship between the immune and the neuroendocrine systems.

All-trans retinoic acid and in vitro cytokine production by acute promyelocytic leukemia cells

Leukemic cells spontaneously secrete cytokines involved in the proliferation of the clone; in this study we evaluated the effects of all-trans retinoic acid (ATRA) on the in vitro autocrine production of cytokines by acute myeloid leukemia cells. Thirty acute nonlymphoid leukemia cases (ANLL) (10 APL and 20 ANLL of other cytotypes than APL) were studied; the in vitro secretions of IL-1 alpha, IL-3, IL-4, IL-6, IL-10, G-CSF, GM-CSF, TNF-alpha were tested with and without ATRA addition. After 5 d exposure to ATRA 10(-6) M APL-treated samples showed a significant reduction of IL-6 (p = 0.008) and GM-CSF (p = 0.03) and a significant increase of IL-1 alpha (p = 0.01) production, if compared to untreated APL samples. No difference was seen in IL-3, IL-10 and IL-4 productions; G-CSF production resulted absent in all but 3 APL cases, in which addition of ATRA determined increase in the production. Interestingly, the 3 G-CSF-producing cases did not obtain clinical remission with ATRA; GM-CSF and IL-6 were spontaneously produced by all the cases, and 7 of 10 APL patients subsequently obtained complete remission after induction. TNF-alpha was produced only in 1 case. No statistical difference was seen in all the productions obtained from other than promyelocytic acute leukemic cells, both with and without ATRA addition. However, it is noteworthy that the production of IL-6 was more than twice as high in ANLL non-APL than in APL cases. In conclusion, these data could thus suggest possible complementary mechanisms of the exhaustion of the leukemic clone upon treatment with ATRA.

Immunocytochemical evidence of PDGF- and TGF-beta-like molecules in invertebrate and vertebrate immunocytes: an evolutionary approach

Immunoreactive platelet-derived growth factor-AB and transforming growth factor-beta 1 were demonstrated in invertebrate and vertebrate immunocytes by an immunocytochemical procedure. These factors are only present in phagocytic cells among invertebrate immunocytes, whereas in vertebrate immunocytes they are found in monocytes, granulocytes, lymphocytes, thrombocytes and platelets. These results, in agreement with previous reports, represent further evidence in favour of the hypothesis that Nature has followed a conservative strategy in using a common pool of signal molecules that have been highly conserved throughout evolution.

Retinoids increase idarubicin cytotoxicity in human myeloid leukemia cell lines

All-trans-retinoic acid (ATRA) has proven useful in acute promyelocytic leukemia (APL). In order to reduce the side effects and to improve the efficacy of this compound, conventional chemotherapy, and anthracyclines in particular, are frequently added either during remission induction or in consolidation therapy. In this study we aimed at investigating the rationale of the combination of ATRA plus idarubicin in two human leukemic cell lines, HL-60 and K562, that display a different sensitivity to ATRA treatment. The effects of ATRA were compared with those of two clinically active retinoids, 13-cis-retinoic acid (13-cis-RA) and 9-cis-retinoic acid (9-cis-RA). Both in HL-60 and in K562 cells, the majority of the combinations of ATRA and idarubicin were synergistic, while the combinations with 9-cis-RA and 13-cis-RA were more effective in HL-60 and K562 cells, respectively. A 72 h pre-incubation with retinoids was able to further increase the cytotoxicity of ATRA plus idarubicin in the two cell lines. Intracellular idarubicin accumulation was enhanced by retinoids, as demonstrated by a cytofluorimetric method. Our results could contribute to provide a rationale for ATRA plus idarubicin combinations not only in APL but also in acute leukemia of other cytotypes.

Biological and clinical significance of in vitro prednisolone resistance in adult acute lymphoblastic leukaemia

It has been reported that in vitro prednisolone (PDN) resistance provides a prognostic value in childhood acute lymphoblastic leukaemia (ALL). This study aimed at investigating the biological and clinical significance of in vitro PDN resistance in adult ALL. Blast cells from 30 patients were exposed to PDN (0.1 microM-35 microM) and cytotoxicity was determined by the soluble tetrazolium formazan 2,3-bis (2-methoxy-4-nitro-5-sulphophenyl)-5-[(phenylamino) carbamyl]-2H-tetrazolium hydroxyde (XTT) colorimetric assay. The IC50 (defined as the drug concentration that results in 50% growth inhibition) varied greatly among the samples, from 0.3 microM to > 35 microM; 15 microM was subsequently chosen as IC50-cut-off point between in vitro resistant and sensitive cases. PDN-induced cytotoxicity was significantly related to apoptosis, as demonstrated by regression analysis; in sensitive cases, however, the percentage of apoptotic cells after in vitro PDN treatment was significantly increased compared with control (p = 0.002). Immunofluorescence evaluation of intracellular BCL-2 protein showed an equal percentage of positive cells in the two groups, but in resistant cells a higher mean fluorescence intensity (p = 0.04) was demonstrated. In vitro sensitive and resistant patients did not display differences in clinical characteristics, in cytological, karyotypic and immunophenotypic features and in the outcome of induction therapy. Disease-free survival (DFS), however, was significantly better in sensitive patients (p = 0.02).

Nuclear translocation of protein kinase C-alpha and -zeta isoforms in HL-60 cells induced to differentiate along the granulocytic lineage by all-trans retinoic acid

We investigated whether members of the protein kinase C (PKC) family of enzymes were involved in the nuclear events underlying granulocytic differentiation induced by 10(-6) M all-trans retinoic acid (ATRA) in HL-60 cells. PKC activity was analysed by using a serine substituted specific peptide which enabled the evaluation of the whole catalytic activity of both Ca2+ -dependent and Ca2+ -independent PKC isoforms. In parallel, the subcellular distribution of various PKC isoforms was evaluated by Western blot, immunoprecipitation and in situ immunocytochemistry analyses. The level of PKC catalytic activity in the nuclei of HL-60 cells significantly (P < 0.01) and progressively increased from 1 h of ATRA treatment onwards. Consistently, PKC-alpha and -zeta showed a striking and selective accumulation inside the nucleus upon treatment with ATRA. On the other hand, PKC-beta I and -beta II, the only two other isoforms present at nuclear level, did not show any significant modification upon ATRA treatment. The remaining PKC isoforms were not detectable inside the nucleus and showed only modest and non-significant variations, also in whole cell homogenates, upon ATRA treatment, except PKC-delta which showed a progressive down-regulation. Our data suggest that a selective nuclear translocation of PKC-alpha and -zeta might be involved in the process of granulocytic differentiation induced by ATRA in HL-60 cells.

FLAG (fludarabine, cytarabine, G-CSF) as a second line therapy for acute lymphoblastic leukemia with myeloid antigen expression: in vitro and in vivo effects

Thirteen consecutive adult patients with primary refractory (n = 5) or relapsed (n = 8) acute lymphoblastic leukemia (ALL) were treated by an induction schedule (FLAG) consisting of Fludarabine (30 mg/sqm/d) plus high dose Cytarabine (HD-ara-C: 2 g/sqm/d) (d 1-5) and G-CSF (from d O to polymorphonuclear recovery). Patients achieving complete remission (CR) were administered a second FLAG course as consolidation and were then submitted to an individualized program of post-remission therapy, depending on the patient's age and performance status. CR was achieved in 8/12 evaluable cases (67%). The median CR duration was 22.5 w. CR attainment was significantly related to the co-expression of lymphoid and myeloid antigens. ALL/My+ patients achieved CR in 6/6 evaluable cases vs. 2/6 for ALL/My+. In vitro 3H ara-C incorporation into cellular DNA resulted significantly increased by Fludarabine (in 7/9 tested cases) and, furthermore, by the association of Fludarabine G-CSF in 5 evaluable ALL/My+ cases; in contrast, no effect of G-CSF addition to Fludarabine was observed in 4 ALL/My. Myelosuppression was observed in all patients: the median time to neutrophils > 0.5 x 10(9)/1 was 16.3 d (range 13-22) and 16.2 d (range 9-29) to platelets > 20 x 10(9)/1. Nonhematological toxicity was minimal. In conclusion, FLAG is an active and tolerable combination in refractory ALL, particularly in cases with myeloid antigen expression where G-CSF appears to improve efficacy, probably increasing ara-C incorporation into the DNA of leukemic cells.

In vitro culture with prednisolone increases BCL-2 protein expression in adult acute lymphoblastic leukemia cells

The presence of BCL-2 gene rearrangement has been detected also in cellular populations lacking the t(14;18) chromosomal translocation, such as B-lineage acute lymphoblastic leukemia (ALL) cells. It has been reported that overexpression of BCL-2 is related to resistance to glucocorticoid-induced apoptosis. In this study, we aimed to evaluate whether in vitro culture with prednisolone (PDN) could modify the expression of BCL-2 protein. ALL cells from 21 patients were incubated for 72 hr with or without a minimally lethal (IC12) dose of PDN. In vitro culture with PDN did not affect the percentage of positive cells, even though the mean fluorescence index was significantly increased (P = 0.0001), thus indicating a higher level of protein production. These data could suggest a possible mechanism of drug resistance after treatment with PDN.

The neuroimmunology of stress from invertebrates to man

Stress can be seen as the body's most important and complex reaction to ensure survival involving the neuroendocrine systems and a variety of other organs. The investigation of the evolutionary bases of stress argues that the basic mechanisms and molecules involved in stress (CRH, ACTH, glucocorticoids, biogenic amines and cytokines) are fundamentally similar and well preserved throughout evolution in different species and taxa. A review of available data highlights that the involvement of immunity during stress response has a strong evolutionary basis and is not a mere consequence of glucocorticoid hormone release. We propose that the evolutive cellular bases of stress are to be identified in immune cells, such as invertebrate hemocytes, producing a variety of cytokine-like molecules, capable at the same time of producing a variety of hormone- and neuropeptide-like molecules and of performing a proto-stress response (release of biogenic amines). We conclude that stress, a highly conserved reaction remarkably similar in different species and taxa, is a fundamentally positive type of adaptive reaction.

All-trans retinoic acid in the treatment of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a group of hematopoietic disorders characterized by uni- or multilineage maturation defects of the bone marrow. Controversial therapeutic results have been obtained using growth factors or differentiating agents such as 13-cis retinoic acid. In this pilot study we evaluated the effects of all-trans retinoic acid (ATRA) in 10 MDS patients (5 male, 5 female). Six patients had refractory anemia (RA), 1 had refractory anemia with excess of blasts (RAEB), and 3 had refractory anemia with excess of blasts in transformation (RAEB-t). All patients received the same dose of ATRA (45 mg/sqm/day) orally for 6 weeks. A rise in hemoglobin concentration > 1g/dl was observed in 3/10 patients, while 5/10 patients showed an increase in granulocyte count > 0.5 x 10(9)/l without concomitant increase in the percentage of blast cells in the bone marrow. A rise in the platelet count > 50 x 10(9)/l was observed in 1/10 patients. All the effects were transient and maximal responses were obtained by the fourth week of treatment. Thereafter, the peripheral blood counts started to drop again, reaching pre-therapy values by the end of the treatment. This phenomenon could be attributed either to the exhaustion of an ATRA-responding cell pool, the development of cellular resistance to ATRA or to a reduction of plasma ATRA levels after prolonged treatment. According to our results, it seems that ATRA might have therapeutic efficacy in MDS, particularly if its effect could be improved by combinations with other differentiating agents or growth factors.

Evidence for the presence of immunoreactive POMC-derived peptides and cytokines in the thymus of the goldfish (Carassius c. auratus)

The presence of immunoreactive pro-opiomelanocortin (POMC)-derived peptides (adrenocorticotropin hormone, beta-endorphin, alpha-melanocyte-stimulating hormone) and of cytokine-like molecules [interleukin (I)-1 alpha, IL-1 beta, IL-2, Il-6, tumour necrosis factor-alpha] was demonstrated in periodic acid-Schiff-positive epithelial cells in the thymus of the goldfish (Carassius c. auratus) using immunocytochemical procedures. POMC-derived peptide- and cytokine-like molecules were localized in the same cell type. Lymphocytes were negative for all the above mentioned molecules. Despite the smaller number of cells positive for neuropeptide- and cytokine-like molecules, our findings suggest that immune-neuroendocrine interactions are likely to occur in the thymus of goldfish.