Effect of cholecystokinin and gastrin on human peripheral blood lymphocyte functions, implication of cyclic AMP and interleukin 2

Expression and Regulation of Cholecystokinin Receptor in the Chicken's Immune Organs and Cells

Cholecystokinin (CCK) is a neuropeptide that affects growth rate in chickens by regulating appetite. CCK peptides exert their function by binding to two identified receptors, CCKAR and CCKBR in the GI tract and the brain, respectively, as well as in other organs. In mammals, CCK/CCKAR interactions affect a number of immunological parameters, including regulation of lymphocytes and functioning of monocytes. Thus, food intake and growth can potentially be altered by infection and the resulting inflammatory immune response. It is uncertain, however, whether chicken express CCKAR in immune organs and cells, and, if so, whether CCKAR expression is regulated by pathogen derived inflammatory stimuli. Herein, we identify expression of CCKAR protein in chicken peripheral blood mononuclear cells (PBMC) including monocytes, and expression of the CCKAR gene in PBMC, thymus, bursa, and spleen, in selected commercial and pure chicken breeds. Further, stimulation with various types of E. coli heat-labile enterotoxins or lipopolysaccharide significantly regulated expression of CCKAR on monocytes in the different breeds. Ligation of CCKAR with antibodies in PBMC induced mobilization of Ca²⁺, indicating that CCKAR is signal competent. Injection with polyinosinic: polycytidylic acid (poly I:C), a synthetic analogue of double stranded viral RNA that binds Toll-Like Receptor-3 (TLR3), also regulated gene expressions of CCKAR and proinflammatory cytokines, in the different breeds. Interestingly, variations in the expression levels of proinflammatory cytokines in the different breeds were highly correlated with CCKAR expression levels. Taken together, these findings indicate that the physiological function of CCKAR in the chicken is tightly regulated in immune organs and cells by external inflammatory stimuli, which in turn regulate growth. This is the first report CCKAR expression in immune organs and cells, in any species, and the initial observation that CCKAR is regulated by inflammatory stimuli associated with bacterial and viral infection.

Vitamin B(12) and folic acid imbalance modifies NK cytotoxicity, lymphocytes B and lymphoprolipheration in aged rats

Different vitamin B₁₂ and folic acid concentrations could exacerbate the immune response. The aim was to evaluate different dietary folic acid and vitamin B₁₂ levels on the immune response in aged rats. Male Sprague Dawley aged rats were assigned to three folic acid groups (deficient, control, supplemented) each in absence of vitamin B₁₂ for 30 days. Several parameters of innate and acquired immune responses were measured. Serum and hepatic folate levels increased according to folic acid dietary level, while vitamin B₁₂ levels decreased. There was a significant decrease in natural killer cell-mediated cytotoxicity in the spleen for the vitamin B₁₂ deficient diet and folic acid control diet groups. Significant changes in CD45 lymphocyte subsets were also observed according to dietary imbalance. Lymphoproliferative response to concanavalin A and phytohemagglutinin did not differ significantly between groups. The spleen response to lipopolysaccharide increased significantly, but was unmodified for the other organs. An imbalance between dietary vitamin B₁₂ and folic acid concentrations alters some immunological parameters in aged rats. Therefore, the ratio between folate and vitamin B₁₂ could be as important as their absolute dietary concentrations.

Gastrin-deficient mice have disturbed hematopoiesis in response to iron deficiency

Gastrins are peptide hormones important for gastric acid secretion and growth of the gastrointestinal mucosa. We have previously demonstrated that ferric ions bind to gastrins, that the gastrin-ferric ion complex interacts with the iron transport protein transferrin in vitro, and that circulating gastrin concentrations positively correlate with transferrin saturation in vivo. Here we report the effect of long-term dietary iron modification on gastrin-deficient (Gas(-/-)) and hypergastrinemic cholecystokinin receptor 2-deficient (Cck2r(-/-)) mice, both of which have reduced basal gastric acid secretion. Iron homeostasis in both strains appeared normal unless the animals were challenged by iron deficiency. When fed an iron-deficient diet, Gas(-/-) mice, but not Cck2r(-/-) mice, developed severe anemia. In iron-deficient Gas(-/-) mice, massive splenomegaly was also apparent with an increased number of splenic megakaryocytes accompanied by thrombocytosis. The expression of the mRNA encoding the iron-regulatory peptide hepcidin, Hamp, was down-regulated in both Cck2r(-/-) and Gas(-/-) mice on a low-iron diet, but, interestingly, the reduction was greater in Cck2r(-/-) mice and smaller in Gas(-/-) mice than in the corresponding wild-type strains. These data suggest that gastrins play an important direct role, unrelated to their ability to stimulate acid secretion, in hematopoiesis under conditions of iron deficiency.

Gastrin, inflammation, and carcinogenesis

PURPOSE OF REVIEW

Chronic infection of the gastric mucosa with Helicobacter pylori has long been recognized as a significant risk factor for gastric cancer, and indeed, this model represents the prototypical inflammation-associated cancer. In this review, we present the latest clinical and experimental evidence showing that gastrin peptides and their receptors [the cholecystokinin (CCK2) receptors] potentiate the progression of gastric cancer and other gastrointestinal malignancies in the presence of inflammation.

RECENT FINDINGS

We highlight the feed-forward mechanisms by which gastrin and CCK2 receptor expression are upregulated during inflammation and in gastrointestinal cancers, summarize gastrin's proinflammatory role by inducing the production of cyclooxgenase-2 (COX-2) and interleukin-8 (IL-8), and relate evidence suggesting that gastrin and their receptors modulate the function of immune cells and fibroblasts following cellular stress, injury, repair, as well as during cancer progression.

SUMMARY

We discuss trends for future studies directed toward the elucidation of gastrin peptides' role in regulating intercellular molecular signaling mechanisms between local and circulating immune cells, fibroblasts, epithelial cells, and other cell types in the microenvironments of inflammation-related cancers. Elucidation of the molecular and cellular pathways that relate inflammation with cancer may provide additional opportunities to develop complementary therapies that target the inflammatory microenvironment of the cancer.

Vitamin E ingestion improves several immune functions in elderly men and women

The effects of diet supplementation with the antioxidant vitamin E (200 mg daily) on several blood neutrophil, lymphocyte and natural killer cell functions have been investigated in healthy elderly men and women before supplementation, after 3 months of supplementation and 6 months after the end of supplementation (post-supplementation). In parallel, samples of healthy adult men and women were used as age controls. In elderly men and women, an impairment of immune functions was observed in comparison with the respective adult controls and the intake of vitamin E resulted in a significant enhancement of immune parameters in both elderly men and women, bringing their values close to those in the adults. These effects were not found in post-supplementation samples in several but not in all functions. The present findings suggest that supplementation with vitamin E can produce an improvement of immune functions and therefore of health in aged people.

Gene expression profiling reveals upregulation of Tlr4 receptors in Cckb receptor deficient mice

The cholecystokinin B (2) receptor knockout (Cckbr KO) protects against allodynia induced by chronic constriction injury (CCI). The mechanism of this phenomenon is unknown, but must involve persistent changes in pain modulation and/or inflammatory pathways. We performed a gene expression study in two brain areas (midbrain and medulla) after surgical induction of CCI in Cckbr KO and wild-type (wt) control mice. The patterns of gene expression differences suggest that the immune system is activated in higher brain structures following CCI in the wt mice. The strongest differences include genes related to the MAPK pathway activation and cytokine production. In Cckbr KO mice this expressional pattern was absent. In addition, we found significant elevation of the Toll-like receptor 4 (Tlr4) in the supraspinal structures of the mice with deleted Cckbr compared to wt control mice. This up-regulation is most likely induced by the deletion of Cckbr. We suggest that there is a functional deficiency in the Tlr4 pathway which disables the development of neuropathic pain in Cckbr KO mice. Indeed, real time PCR analysis detected a CCI-induced upregulation of Tlr4 and Il1b expression in the lumbar region of wt but not Cckbr KO mice. Gene expression profiling indicates that elements of the immune response are not activated in Cckbr KO mice following CCI. Our findings suggest that there may be a role for CCK in the regulation of innate immunity.

CCK-8 inhibits LPS-induced IL-1beta production in pulmonary interstitial macrophages by modulating PKA, p38, and NF-kappaB pathway

The neuropeptide cholecystokinin octapeptide (CCK-8) inhibits inflammation by downregulating the expression of proinflammatory cytokines, such as tumor necrosis factor alpha and interleukin (IL) 1beta during endotoxin shock. However, the signaling mechanism of CCK-8 action has not yet been clearly elucidated. In this study, we have examined the possible signaling pathways by which CCK-8 inhibits lipopolysaccharide (LPS)-induced IL-1beta production in rat pulmonary interstitial macrophages. In macrophages, LPS is known to activate p38 kinase, which, in turn, activates nuclear factor (NF)-kappaB to induce IL-1beta production. We found that the pretreatment of cells with CCK-8 blocked the LPS-induced p38 kinase, NF-kappaB activation, and IL-1beta production. Furthermore, CCK-8 treatment activated the cyclic adenosine monophosphate-protein kinase A signaling pathway and H-89 (a protein kinase A inhibitor), abrogated the inhibitory effects of CCK-8 on p38 kinase activation and NF-kappaB activation. In addition, we also demonstrate that the specific antagonist to CCK-1 receptor (CCK-1R) and CCK-2 receptor (CCK-2R) abrogate the CCK action, and that the effects of the antagonist specific to CCK-1R is more significant. These results suggest that these responses were mediated through CCK-1R and CCK-2R, and CCK-1R might be the major receptor responsible for the anti-inflammatory effect of CCK-8. Taken together, our results indicate that the stimulation of cyclic adenosine monophosphate-protein kinase A signaling pathway by CCK-8 through CCK-1R and CCK-2R inhibits the LPS-induced activation of p38 kinase and NF-kappaB to block the IL-1beta production in rat pulmonary interstitial macrophages.

Effect of ppMCH derived peptides on PBMC proliferation and cytokine expression

The mRNA encoding prepro-Melanin concentrating hormone (ppMCH) is mainly expressed in the central nervous system but has also been detected at lower amount in many peripheral tissues including spleen and thymus. At the peptide level however, several forms of the precursor can be detected in these tissues and are sometimes expressed at similar levels compared to brain. In the present work, we have studied the in vitro action of a wide range of concentration (1 nM to 1 microM) of the different peptides encoded by ppMCH i.e. neuropeptide glycine-glutamic acid (NGE), neuropeptide glutamic acid-isoleucine (NEI), Melanin concentrating hormone (MCH) and the dipeptide NEI-MCH on peripheral blood mononuclear cells (PBMC) proliferation and cytokine production following anti-CD3 stimulation. Among them only MCH decreased PBMC proliferation with a maximal effect of 35% at 100 nM. Moreover as demonstrated by using ELISA, MCH significantly decreases IL-2 production by 25% but not IL-4, INF-gamma or TNF-alpha expression. Interestingly, exogenous IL-2 decreases significantly MCH-mediated inhibition, suggesting that it is an important downstream mediator of MCH action. Finally, we showed that after 7 to 9 days of incubation, MCH also inhibits proliferation of non-stimulated PBMC. Altogether, these data demonstrate that fully mature MCH modulates proliferation of anti-CD3 stimulated PBMC partially through regulation of IL-2 production.

Impairment of several immune functions in anxious women

OBJECTIVE

Controversial results concerning immune function changes taking place in anxious subjects have been obtained. The aim of the present work was to study immune function in a group of anxious women.

METHODS

Thirty-three anxious and 33 nonanxious age-matched women were included. Anxiety levels were determined by the Beck Anxiety Inventory. Peripheral blood samples were collected, and several leukocyte functions, as well as cytokine release, were studied. Plasma cortisol levels and total antioxidant capacity were also evaluated.

RESULTS

The results showed diminished chemotaxis, phagocytosis, lymphoproliferation in response to phytohemagglutinin mitogen, natural killer activity, and interleukin-2 release, and augmented superoxide anion levels and tumor necrosis factor-alpha release in anxious women. Plasma cortisol was increased, while total antioxidant capacity was lowered in those subjects.

CONCLUSIONS

The findings suggest impaired immune function and cytokine release in anxious women. This might be related to increased cortisol secretion, which would lead to oxidative stress reflected in lowered plasma total antioxidant capacity.

Gastrin induces leukocyte-endothelial cell interactions in vivo and contributes to the inflammation caused by Helicobacter pylori

Gastric mucosal inflammation causes hypergastrinemia, and gastrin receptors have been detected in several leukocyte types. We have analyzed whether gastrin affects the leukocyte-endothelial cell interactions in vivo by monitoring leukocyte rolling, adhesion, and emigration in rat mesenteric venules using intravital microscopy. Mesenteric superfusion with exogenous gastrin increased these processes in a concentration- and time-dependent manner, effects prevented by the cholecystokinin (CCK)-2 receptor antagonists (proglumide, L-365,260) but not by the CCK-1 receptor antagonist devazepide. A similar response was induced by exogenous CCK or endogenously released gastrin. CCK-2 receptors were localized in mesenteric macrophages and polymorphonuclear leukocytes. This effect of gastrin is not modulated by somatostatin and is independent of the endogenous release of histamine. To analyze whether hypergastrinemia elicited by Helicobacter pylori (HP) modulates the inflammation induced by the germ, rats were chronically administered with an extract of a CagA+/VacA+ strain of HP. This protocol increased gastrinemia and induced an inflammatory response in the rat mesentery. Blockade of CCK-2 receptors attenuated this response and induced a qualitative change in the leukocyte infiltrate suggestive of a receding inflammatory process. Our results reveal a new proinflammatory role of gastrin that seems to contribute to the maintenance of the inflammation elicited by HP components.

Effect of cholecystokinin octapeptide on diacylglycerol-PKC signaling pathway in rat pulmonary interstitial macrophages stimulated by lipopolysaccharide

AIM

To investigate the effect of cholecystokinin octapeptide (CCK-8) on the diacylglycerol-protein kinase C (DAG-PKC) signaling pathway in rat pulmonary interstitial macrophages (PIM) stimulated by lipopolysaccaride (LPS).

METHODS

The PIM from rat lung tissues were isolated using the collagenase digestion method combined with alveolar lavage and pulmonary vessel perfusion. DAG content and PKC activity were measured by radioenzymatic assay. The translocation of PKCzeta was determined by semi-quantitative immunoblot analysis.

RESULTS

CCK-8, at high concentrations (1 x 10(-6) - 1 x 10(-5) mol/L), decreased DAG content and inhibited PKC activity and PKCzeta translocation compared with that in rat resting PIM of a control group (P< 0.01). LPS increased DAG content, and promoted PKC activity and PKCzeta translocation (P< 0.01). CCK-8 decreased LPS-induced DAG content and inhibited LPS-induced PKC activity and PKCzeta translocation significantly at 1 x 10(-8) - 1 x 10(-5) mol/L (P< 0.01). This inhibitory effect of CCK-8 could be abrogated partly by proglumide (non-selective CCK receptor antagonist), CR-1409 (selective CCK-A receptor antagonist), and CR-2945 (selective CCK-B receptor antagonist) in a concentration-dependent manner (P< 0.01).

CONCLUSION

CCK-8 was a negative modulator of the DAG-PKC signaling pathway in rat resting PIM, which is very important for maintaining body homeostasis. It significantly inhibited LPS-induced DAG content, PKC activity and PKCzeta translocation in a concentration-dependent manner. The CCK receptor, especially the CCK-A receptor, might play a major role in this process.

An immunomodulator used to protect young in the pouch of the Tammar wallaby, Macropus eugenii

Eugenin [pGluGlnAspTyr(SO(3))ValPheMetHisProPhe-NH(2)] has been isolated from the pouches of female Tammar wallabies (Macropus eugenii) carrying young in the early lactation period. The sequence of eugenin has been determined using a combination of positive and negative ion electrospray mass spectrometry. This compound bears some structural resemblance to the mammalian neuropeptide cholecystokinin 8 [AspTyr(SO(3))MetGlyTrpMetAspPhe-NH(2)] and to the amphibian caerulein peptides [caerulein: pGluGlnAspTyr(SO(3))ThrGlyTrpMetAspPhe-NH(2)]. Eugenin has been synthesized by a route which causes only minor hydrolysis of the sulfate group when the peptide is removed from the resin support. Biological activity tests with eugenin indicate that it contracts smooth muscle at a concentration of 10(-9) M, and enhances the proliferation of splenocytes at 10(-7) M, probably via activation of CCK(2) receptors. The activity of eugenin on splenocytes suggests that it is an immunomodulator peptide which plays a role in the protection of pouch young.

Omeprazole treatment: genotoxicity biomarkers, and potential to induce CYP1A2 activity in humans

Omeprazole is one of the most used acid-suppressing medications. This fact emphasizes the questions concerning the safety of this compound. Healthy volunteers (n=33) were included in this prospective study. All study subjects were analysed for their CYP2C19 genotype. Of the 33 individuals, 24 were homozygous for the wild type CYP2C19*1 allele, 7 were heterozygous for the CYP2C19*2 variant allele, and 2 were homozygous for the CYP2C19*2 variant allele. Before and after 14 days of omeprazole treatment at a daily dose of 20 mg, one blood sample was taken from each individual to determine five cytogenetic biomarkers of genotoxicity: chromosome aberrations, micronuclei, proliferating rate index, sister chromatid exchanges, and mitotic index. The only significant change was that of a weak increase in micronuclei count after treatment in relation to baseline values (day 0) (P = 0.026). To assess the potential of omeprazole to induce P450 CYP1A2, the urinary ratio AFMU+1X+1U/17U in the interval of 4-5 hours after caffeine intake was calculated twice (days 0 and 15), using the caffeine test in 27 of the 33 individuals. This result suggests that omeprazole does not increase CYP1A2 activity after 14 days of treatment.

Lymphoid distribution in the migratory gull Larus ridibundus

We studied the distribution of lymphocytes in the main lymphoid tissues (blood, spleen and thymus) of the gull Larus ridibundus, searching for variations that might depend on the migratory cycle. We also looked for sex- and age-associated differences in lymphoid redistribution. In L. ridibundus, lymphocytes are the most commonly observed leukocyte subpopulation in blood. Moreover, changes in the distribution of lymphocytes in the lymphoid tissue occur, depending on the migratory period. The proportion of these cells in spleen is greater in the post-migratory and pre-migratory periods compared to the non-migratory period. The percentages of circulating lymphocytes are high in the pre-migratory period, but depletion occurs in the post-migratory period. In contrast, the age or the sex of the animals did not confer any major differences on the lymphoid distribution.

Anti-inflammatory effect of cholecystokinin and its signal transduction mechanism in endotoxic shock rat

AIM: To study the anti-inflammatory effects of cholecystokinin-octapeptide (CCK-8) on lipopolysaccharide (LPS)-induced endotoxic shock (ES) and further investigate its signal transduction pathways involving p38 mitogen-activated protein kinase (MAPK) and IκB-α.

METHODS: Eighty-four rats were divided randomly into four groups: LPS (8 mg·kg^-1, iv) induced ES; CCK-8 (40 μg·kg^-1, iv) pretreatment 10 min before LPS (8 mg·kg^-1); CCK-8 (40 μg·kg^-1, iv) or normal saline (control) groups. The inflammatory changes of lung and spleen, phagocytic function of alveolar macrophage, quantification of inflammatory cells in bronchoalveolar lavage (BAL) were investigated in rats by using hematoxylin and eosin (HE) staining, phagocytosis of Candida albicans and differential cell counting. Nitric oxide (NO) production in serum, lung and spleen was measured with the Griess reaction. The mechanism involving p38 MAPK and IκB-α signal pathways was investigated by Western blot.

RESULTS: Inflammatory changes of lung and spleen induced by LPS were alleviated by CCK-8, the increase of NO induced by LPS in serum, lung and spleen was significantly inhibited and the neutrophil infiltration in BAL was significantly reduced by CCK-8. The number of neutrophils was (52 ± 10) × 10⁶ cells•L^-1 in LPS group, while it decreased to (18 ± 4) × 10⁶ cells•L^-1 in CCK-8+LPS (P < 0.01). The phagocytic rate of CCK-8 group increased to (62.49 ± 9.49)%, compared with control group (48.16 ± 14.20)%, P < 0.05. The phagocytosis rate was (85.14 ± 4.64)% in LPS group, which reduced to (59.33 ± 3.14)% in CCK-8+LPS group (P < 0.01). The results of phagocytosis indexes showed similar changes. CCK-8 may play an important role in increasing the expression of p38 MAPK and decreasing the degradation of IκB-α in lung and spleen of ES rats.

CONCLUSION: CCK-8 can result in anti-inflammatory effects, which may be related to activation of p38 MAPK and inhibition on the degradation of IκB-α.

Seasonal changes in peripheral blood leukocyte functions of the turtle Mauremys caspica and their relationship with corticosterone, 17-beta-estradiol and testosterone serum levels

We have studied the most representative functions of lymphocytes such as adherence to substrate, mobility directed to a chemoattractant gradient (chemotaxis), proliferative response to mitogens and antibody-dependent cellular cytotoxicity (ADCC), as well as natural killer (NK) activity in peripheral blood cells from the turtle Mauremys caspica, and the seasonal changes of these functions in both female and male animals. The plasma levels of steroid hormones were determined to study their relationship with the immune functions. Our results show high chemotaxis, lymphoproliferative response and ADCC as well as NK activity in winter when the levels of corticosterone, testosterone and 17-beta-estradiol were depleted. Proliferative responses to phytohaemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) were increased in spring correlating with low levels of corticosterone and testosterone in middle and late spring. In summer, the proliferative response was decreased but adherence, chemotaxis, ADCC and NK activity were increased, although steroid hormones showed high plasma levels. In autumn, a depletion of both the hormone levels and the immune response were found except for adherence to substrate. The immune functions studied were strikingly influenced by the seasonal cycle, which induced a different pattern of response depending on the function analyzed. Moreover, these immune cells showed a different degree of dependence on steroids in relation to the function and the season considered, suggesting the existence of other factors that modulate the immune response studied.

Age-related changes in the neuropeptide Y effects on murine lymphoproliferation and interleukin-2 production

Neuropeptide Y (NPY) modulates several aspects of the immune response but it is not known whether NPY responsiveness is altered with aging. In this work, the in vitro effect of NPY at concentrations ranging from 10(-)(14) M to 10(-)(7) M on lymphoproliferation has been studied in spleen, axillary node and thymus leukocytes from young, adult, mature and old BALB/c mice. The spontaneous proliferation of spleen lymphocytes from young mice was significantly stimulated by NPY. In response to the mitogen Con A, lymphoproliferation and IL-2 release by lymphocytes were inhibited significantly by NPY, these effects disappearing with aging. The results show that NPY is a modulator of lymphoproliferation and that this effect disappears progressively with age. Moreover, this regulatory role of NPY may be carried out through a decrease in IL-2 production.

Anti-oxidants as modulators of immune function

In order to confirm the hypothesis of the immunomodulating action of anti-oxidants (bringing back altered immune function to more optimum values), the possibility that anti-oxidants may be useful in two experimental models of altered immune function has been studied. The first is a pathological model, that is, lethal murine endotoxic shock caused by an LPS injection of 100 mg/kg, in which the lymphocytes show increased adherence and depressed chemotaxis. The injection of N-acetylcysteine (150 mg/kg), which increased both functions in control animals, decreased adherence and increased chemotaxis in mice with endotoxic shock. The second is a physiological model; aged human subjects (70 +/- 5-year-old men) who, in their largest segment of population ('standard' group) showed an increased lymphocyte adherence and decreased lymphoproliferative response to mitogens compared with younger adults. The ingestion of vitamin E (200 mg daily for 3 months in this standard group) lowered adherence and stimulated lymphoproliferation. However, a smaller segment of the human population tested showed 'non-standard' values in these lymphocyte functions, that is, very low adherence and very high proliferation. In those subjects, vitamin E showed the opposite effects, namely adherence increase and depressed lymphoproliferation. In both age groups of men, these functions reached adult levels after vitamin E ingestion. These data suggest that anti-oxidants preserve adequate function of immune cells against homeostatic disturbances such as those caused by endotoxic shock and ageing.

Modulation of murine lymphocyte functions by sulfated cholecystokinin octapeptide

The effects in vitro of the sulfated octapeptide form of cholecystokinin (CCK-8) at concentrations ranging from 10(-13) M to 10(-6) M on several functions of murine lymphocytes were studied, i.e. adherence to substrate, mobility (spontaneous and directed by chemical gradient or chemotaxis) and spontaneous and phytohemagglutinin (PHA)-mediated proliferation. Lymphocytes were obtained from peritoneal suspension as well as from axillary nodes, spleen and thymus of BALB/c mice. CCK-8, at concentrations from 10(-10) M to 10(-8) M, significantly inhibited the mobility capacity and the PHA-induced proliferation and increased the adherence and the spontaneous proliferation of lymphocytes. A dose-response relationship was observed, with a maximum effect on lymphocyte functions at 10(-10) M. In addition, CCK-8 induced a significant decrease in membrane and cytosol protein kinase C (PKC) activity in murine lymphocytes, as well as an increase of intracellular cyclic AMP levels. These results suggest that CCK-8 is a negative modulator of two important lymphocyte functions in the immune response, i.e. mobility and mitogen-induced proliferation, and that the PKC activity inhibition and cAMP increase could be the mechanisms through which CCK inhibits these lymphocyte activities.